All language subtitles for C+Programming+Course+-+Beginner+to+Advanced_en

this complete c plus plus course will

take you from being an absolute beginner

to using advanced c plus plus features

danielle gaguaya teaches this course he

is an experienced software developer and

has created many popular courses

hello guys and welcome to this modern c

plus plus 20 course this is a course

that is going to take you from the

absolute beginning where you know

nothing about c plus plus and you're

going to go all the way to a point where

you can use some advanced features in

the c plus plus programming language

inheritance and polymorphism with the c

plus plus programming language now i'm

convincing you on why you should use c

plus plus but c plus plus is a very

powerful programming language you can

use to do all kinds of crazy things you

can use it to do systems programming you

can build games with it and it is used

in a wide range of areas so you can do a

lot with c plus plus now who is this

course for this course is built for

complete beginners if you already have

some experience with c plus plus you

will still find some good things you can

learn from the course but i am going to

go from the absolute beginning showing

you every little thing showing you the

tools showing you the compilers and the

editor we're going to be using here so

we're going to spend a lot of time

fundamentals by the time you are done

with this course you will understand the

bare fundamentals about c plus we will

spend a lot of time exploring the

procedure programming side of c plus

plus so you're going to be writing

programs that run from top to bottom and

we're going to spend a lot of time in

the editor writing code making sure you

really understand what is going on here

towards the end we're going to learn

about object oriented programming and

inheritance and polymorphism and these

are the tools you're going to be using a

lot in your career as a c plus plus

developer another great feature of this

course is that we spend a lot of time

making sure you understand the tools so

if you don't know what a compiler is if

you don't know what an ide is we're

going to make sure you understand these

things and we're going to spend a lot of

time using these things and by the time

you're done with the course you're going

to be very comfortable using the tools

the editor of choice for the course is

going to be visual studio code so that's

an editor that is going to allow us to

type in the code and give us some things

like a syntax highlighting but we're

going to be connecting our editor to a

background compiler which is going to

make sure our code is transformed

to run on our computer but don't worry

about all that craziness right now we're

going to go in detail about these things

for now i just want you to have a bird's

eye view on what you can expect from the

course here now i hope you know what to

expect from the course but i also expect

you to be ready to take the course and

the requirements are really not that bad

the only requirement is that you have

time set aside to really practice what

you learn from the course here and you

need to have a strong drive and

willingness to learn now if you want to

follow along i am going to share a link

to the github repository for the code i

use in the course so you can check that

out and really follow along if you want

if you want some support we have a

discord server dedicated for our

students so you can join and be part of

the community if you have a question you

can ask but another thing i would

encourage you to do is to also help

others so if you see somebody asking a

question try to help them you're going

to learn a lot that way okay now that

you know a bit about the course let's

talk about myself here my name is daniel

cacoya i am a software engineer i have

and i am a professional c plus plus

developer i do a lot of freelance work i

work for a few companies i do all kinds

of crazy things i also like to teach

others so i have a few courses on udemy

if you are interested in cute you can

check these things out i also have a

trending c plus plus course that you can

check out but don't feel the need to go

and check this ziplesque course out

because a lot is covered in this youtube

course here so that's really all about

me okay now that you have an idea about

the course we're going to head over in

the next lecture and learn about the

tools we're going to be using throughout

the course here go ahead and finish up

welcome to this new chapter where we're

going to be exploring the c plus plus

development tools you need to start

applications and you really need two

kinds of tools the first one is going to

be an editor or an ide through which

you're going to be writing your c plus

plus code we are going to be using

visual studio code as an editor in this

course because it is very easy to

install it is cross-platform it is going

to run well on windows mac and linux and

it supports a host of tools that are

going to make your job easier as a

surplus plus developer but that's not to

say you can't use your favorite ide if

you can but visual studio code is going

to be our main editor in this course so

i would recommend installing it to be

able to follow along with what we do

here now after we have an ide or an

editor in place we will need a compiler

and the compiler is a piece of software

that takes the code we write in the

editor and compiles that into code that

can directly run on the hardware or

binary executable format so this is what

we're going to be doing here we're going

to be typing our code in an editor like

visual studio code we're going to be

kicking off a process to compile our

program and this is going to turn our

program into a format that can run it

directly on the hardware so for example

if you are on a windows machine you're

going to generate a binary executable

that can directly run on windows if you

are on linux we will generate a binary

that can run on linux and the same

concepts can really extend on mac or any

other kind of operating system you might

be working on with the course here so we

need two tools we need an ide or an

editor and a compiler and the tools you

install are going to be depending on the

operating system you are using to watch

the course if you are on windows you're

going to install a set of tools that are

specific to windows if you are on linux

you're going to install a set of tools

for linux if you are on a mac you're

going to install a set of tools specific

to the apple operating system for

desktop now on windows in terms of ides

or integrated development environment it

is possible to use a host of ides for

example you can use code lite it is an

ide you can use you can use microsoft

visual studio but in this course we're

going to be using visual studio code

because it is easy to install it has a

set of features that are really good it

is popular it has a great community

around it i think you're going to have a

great time as a beginner to start

writing your c plus plus programs using

visual studio code that's not to say

that you can't use another ide you can

if you want but i am going to be using

visual studio code in this course here

now on linux we are also going to be

using visual studio code as our editor

in the course but there are other ides

you can use for example you can use cute

creator if you want you can use

codelight you can use a host of other

ides on linux but again visual studio

code is going to be our thing in the

course here and i would recommend

installing it on your linux box if you

are watching this course on the linux

machine so for osx we are also going to

be using visual studio code as our

editor as i said it is cross platforms

it runs where regardless of the

operating system you might be using to

watch the course but if you want you can

ide which is xcode or even code lite all

these are going to work if you want but

again i would recommend going with

visual studio code.plus to start out so

that we have a common ground and you

especially if you are a beginner now

after we have an ide rolling we will

and as we say the compiler is a tool

that is going to transform your c plus

plus code into a format that can run

directly on the hardware so the compiler

you use again is going to depend on the

operating system where you are watching

the course i am going to show you a

bunch of compilers you can use but gcc

is going to be our common base so on

windows i will be using what we call

mingw don't worry if you don't what it

is i am going to show you in a minute

when we install it but this is a project

that brings the gcc compiler on windows

so that we can use it easily and i am

going to show you how to install it but

i am also going to show you how to

install the compiler from microsoft and

the clang llvm compiler these are all

available to you on windows and it is

really easy to install them these days

and i will be using them all if you are

on windows i would recommend installing

them all so that you really have a

chance to try your c plus plus code on

the different compilers and that's a

really good thing to do if you test your

c plus plus code against multiple

compilers you will be increasing your

chances for your code to really be

portable and work on multiple compilers

and operating systems and that cannot be

a bad thing so i would recommend

installing all these compilers if you

are on windows i am also going to show

you how to install two compilers on

linux i am going to show you gcc we're

going to install the shiny new feature

in gcc we're going to install clang lvm

on linux and we will be able to use all

these compilers again if you are on

linux i would recommend installing all

these compilers so that you have a

chance to try your code against multiple

compilers and that's going to make your

code much portable and easier to use on

multiple compilers and platforms on the

mac i am going to show you how to

and i am going to show you how to

install clangle lvm but if you want you

can also install xcode and the compiler

that comes with that for c plus but

development all these are options to you

but again in this course we are mostly

going to be using the gcc compiler so i

would recommend getting a hold of this

if you don't want to install other

compilers if you only have to install

one compiler please install gcc that's

going to be our main compiler in the

course here okay so these are the tools

we need we are going to head over in the

next lecture and show you how to install

the visual studio code editor on windows

and really get started with that

go ahead and finish up here and meet me

in the next lecture this video i am

going to show you how to install a c

plus plus compiler on your windows

operating system so we're going to be

looking at three kinds of compilers

we're going to look at the mingw

compiler which gives us access to a gcc

like compiler on windows we're going to

look at clan llvm which is another

compiler we're going to look at the

now before we talk about any compiler i

would like you to come to google or your

c plus plus compiler support okay so

we're going to choose this little guy

here and this is really going to give us

on which feature is supported by which c

plus plus compiler for example if we are

interested in c plus plus 20 which is

the lattice standard that we have in

simplest plus at the time of recording

this video i am recording of this in

2021 but if we go here we're going to

see c plus plus 20 core features and

we're going to see that we have a list

of what each compiler supports we have

gcc we have clan we have msvc we have

the clan version from the apple company

and if we scroll down we can really see

the features that are supported by each

compiler again gcc is going to be our

choice in this course this is going to

be our main compiler but nothing really

stops you from using the clan compiler

or the msvc compiler and if you happen

to see that your compiler of choice

doesn't support what you need for

example you can see that at the current

time lambdas in an evaluated context are

you can see that it is ready here but

this is a feature you can use both in

gcc and the msvc compiler from microsoft

so keep an eye out on this page here to

know which kind of things you can use in

your compiler if you try something out

and you see that it doesn't work this is

a good place to come and figure out if

your compiler supports the feature that

you are using in this video i am going

to show you how to install the three

most common compilers and those are gcc

clang msvc if you want you can come in

your search engine and type gcc to see

what this is it is a good thing to do to

learn about your tools here you can see

that it is a compiler that is mostly

used on the lenox platform but we can

also use it on windows the latest

installing is eleven two zero i think it

six days ago so it is really fresh and

we're going to be taking advantage of

this another thing i should say here is

that you should install the latest tools

you can get your hands upon this is the

version we're going to be mostly using

in this course but if you are watching

this in the future you're going to have

a newer version i would recommend

installing the latest version or the

newest version you can get your hands

upon so the first we're going to do is

install a gcc compiler on windows i am

going to show you a way we can get both

gcc and clang in one go and to get

access to that please go in your search

engine and type windlabs and this is

going to bring us to this project here

if you want you can click upon this

and this is a cool project by a guy who

is providing worlds for these compilers

so if you want you can just go down here

and look at the lettuce releases again i

lettuce you can get your hands upon in

this case the lettuce happens to be 1120

but in the future this is going to

change you're going to find a version

for 12 or 13 so please grab the newest

version you can get your hands up on now

i want you to install the version that

says that it has llvm and clang so if

you are on a 32-bit version on windows i

would recommend getting this 7-zip

archive on this zip archive here if you

are on 64 i would recommend getting a

hold of this or this little thing here

it doesn't really matter but make sure

you get the latest version you can get

your hands upon and you can see that

this conveniently says latest here so i

am going to download the 64-bit version

on windows i am going to grab the zip

archive here and let's click upon this

this should kick off my download and

this is going to download on my system i

can download this if i want and you're

going to see that it is going to start

downloading here and i am going to wait

for this to finish again this is going

to give us both the gcc compiler and the

clan compiler and this is really like

shooting two birds with one stone so

this is going to be really good i

already have this downloaded so i am

just going to head over to the location

where i have this downloaded i think i

so let's crack this open and go in my

and if i go in my compressed folder i am

going to find winlabs llvm and mingw

this is what you really want but if you

don't want the clan compiler you can

grab the one that doesn't say llvm here

because we really want both of these

compilers we are going to grab the one

that has both the gcc compiler and the

clan compiler if we crack this open

let's open this together so that you can

see what is happening we are going to

have this little folder here if we go in

we're going to find a bin folder if we

go in and crack that open we're going to

that says clang you see we have a clang

compiler we have our clan plus plus

compiler for c plus plus and if we go

down we're going to find our g plus plus

compiler and the gcc compiler this is

what we want so what we are going to do

is extract this somewhere on our system

i put this on my c drive so if you go

here you're going to find mingw64

so all you really have to do is go where

and say extract we're going to right

and say extract to a location and you're

going to specify where you want this to

go and this is going to be extracted or

even if you want you can extract here

this is something i like to do this is

going to show up in the current folder

and you can grab this and paste that in

a location where you want this in my

case i put this in my c drive as i said

here so this is going to be my compiler

now once you have these compilers

installed again we have the clan

compiler we have the gcc compiler if we

go down we're going to find the g plus

plus we even have gdb which is a

debugger we can use to debug c plus plus

applications but we will talk about this

later once you have this i would

recommend putting this in your

environment variables on windows the way

you do this you grab this path well we

have our compilers here and we're going

to copy this this is something i

and on windows 10 you can go on the

and this is going to give us a window in

which we can edit our environment

variables we're going to click on this

little thing this is going to open up on

our system we're going to wait for this

to open up and we're going to have a

window that says system properties we're

going to click on environment variables

here and we can put this in our user

environment variables or on our system

environment variables since i am the

only one using this system i like to put

this in my path for my system variables

so i am going to click on path and click

edit here and i am going to add a path

to my gcc and cloud installation here

you can see that right here if you don't

have this end you can click on new

you're going to have a window here and

you can paste this right in and you can

click ok but i'm not going to do that

because i already have this in here so

what i am going to do is just delete

this let's see if i can delete i can

delete this little guy and i have my

path in here so if you don't have this

in please make sure you have this in

your environment variables so we're

going to cancel out of this but if this

is the first time you do this you should

click ok and one way to test that your

environment variables are working or

even if your compilers are working

is to crack up a command line terminal

so we're going to say cmd on the start

and all you need to do is say g plus

plus just like this dash dash version

if you do this you're going to see

information about your c plus plus

and this is coming from the installation

we just did and for clan you can say

clan plus plus version and this is going

to tell you the information about your

clan compiler installation let's wait

for this to come up i don't know why

it's slow but you can see that we have a

clank compiler the lattice version is

1201 for the gcc compiler the latest

and these are the compilers we can use

to write c plus plus 20 applications

okay so by now we have a gcc compiler

through the main gw project we have a

client llcm compiler on our system we

are also going to see how to get a hold

of the compiler from microsoft and to

get hold of this you need to install

to install microsoft visual studio all

you have to do is come to your favorite

search engine and say microsoft visual

studio we can look at the 2019 version

which is the latest i think and we're

going to click on the download link here

we have as the first link and we're

going to see ways we can download this

little guy now microsoft visual studio

has a community version you can download

for free but we also have a professional

and enterprise versions that we're not

going to care about in this course here

the community version and that's going

to be enough for our purposes here so if

you click on free download here this is

going to download and install the visual

studio compiler you can click on this

little guy and it is going to download

an installer you're going to crack this

open on your system and it is going to

install the visual studio installer so

once you have it installed you can come

and say visual studio installer i think

if you say visual studio you're going to

have this pop-up somewhere on your

system we're going to click on this and

if you crack the installer open you're

going to see a window like this which is

really going to give you a chance to

install the tools you want to use with

ide and in this case we are interested

in desktop development with c plus plus

so we're going to click this little guy

here we're going to take it open

and once you do this you going to click

download and install and this is going

to install the visual studio compiler

with the underlying compiler you see

that this is going to give us access to

the msvc compiler and all kinds of crazy

things we really needed to write c plus

plus applications on windows using the

compiler from microsoft now i have to

say this is going to take some time to

install so if you see that this takes up

20 minutes of your time don't worry this

is really normal because this id and the

compiler behind it and really large

they're not like the gcc or the clan

llvm compilers that we just installed

okay so once you have this ticked or

checked you're going to click on

download or install whatever this button

is saying here this is going to install

both the microsoft visual studio ide

and the compiler from microsoft that you

can use directly to write c plus plus

applications so once we have this open i

am going to suppose that you have this

installed already i am going to close

out of this because i don't want to do

and you're going to have visual studio

installed on your system once you have

this installed you're going to come to

the start menu and say developer

and this is going to bring up two things

one is going to be the developer

powershell for visual studio 2019 and

the other is going to be a command

prompt it doesn't really matter what you

choose i am going to click on the

and once you do this this is going to

give you a terminal or a window through

the environment variables are already in

to start using the compiler from

microsoft and if we come here and type

we're going to see that we're going to

see the information here if this gives

you an error or something you're going

to know that you didn't really install

this properly so please go back and make

sure you have this installed if you have

a problem you can ask me i can do the

best i can to help you out but by this

moment we have three compilers on

windows that we can use for c plus plus

development we have the mingw or the gcc

compiler in our hands we have the klanga

lvm compiler and we have the compiler

from microsoft and now we can install an

ide or an editor and that's going to be

visual studio code and we can connect

that to these compilers so that we can

start writing our own z plus bus 20

applications we are going to head over

in the next lecture and install the

go ahead and finish up here and meet me

there in this lecture i am going to show

you how to install the visual studio

code editor on windows so if you are

watching this course on windows this

video here is going to be a must watch

we are going to head over to our search

engine and type visual studio code this

is going to give you a link where we can

download this cool editor if you want

you can learn all you can about it it is

a source code editor made by microsoft

it supports multiple languages but we're

going to be using that specifically for

c plus plus in the course here here i am

at the page for the editor and you can

read all you want about it but we are

interested in downloading this for

windows if you want you can click on

this download button here but i am just

and have download links for windows if i

want i can click on user installer

system installer you can click on what

you want if you are on a 32-bit system

you're going to download a 32-bit

version i am just going to click on

64-bit here because i am on a 64-bit

in this video we are doing this for

windows so this is going to be our area

of interest here i am going to click on

this download link and i am going to

and i will have a window to start

downloading visual studio code setup

here i can save this file and it is

going to start downloading once it is

downloaded i am going to double click

and really click my way through this

until i have a visual studio code

okay the download is good i can crack

and you're going to see that it is

saying that it has detected that visual

studio code is already running on my

system because i have it installed but

if you don't have it installed you're

going to click your way through and

install this on windows and after you

okay once you start visual studio code

you're going to have a window like this

if you run it for the first time you are

probably going to see a windows with

let's look at the welcome screen you're

going to probably see you're going to

probably see something like this but i

am not sure but the most important thing

is that you're going to have a window

like this with visual studio code the

first thing we want to do for c plus

plus development is going to scroll down

and click on this little thing that says

extensions i am going to click on this

and i am going to go in my search box

here and type c and c plus i can even

type c plus plus it doesn't really

matter and this is an area where we can

install extensions to make visual studio

code do all kinds of crazy things in

this case we are interested in making it

support c and c plus plus so we are

going to click on this extension that

says microsoft here cnc plus plus i am

going to click on this and if you don't

have it installed you can click on the

install button and it is going to

install this little thing and make your

computer ready to use visual studio code

for c plus plus so make sure you install

this and at the end it is going to say

disable or uninstall because it will be

already installed and enabled on your

computer and this is really the end of

our installation video for visual studio

code we are going to head over in the

next video and show you how you can make

a visual studio code use the compilers

that we installed in the previous video

so go ahead and finish up here and meet

in this video we're going to see how to

connect our visual studio code editor to

a compiler so that we can compile our

projects easily through the visual

studio code editor we already have the

ide installed from the last two previous

lectures when we have a compiler

installed in the last lecture we

installed the gcc compiler through the

mingw project we installed the clangela

vm compiler we even installed the

compiler from microsoft now we're going

to connect the ide to the compiler to

make it really easy to compile c plus

plus applications using these tools here

what i am going to do is really set up a

template project we're going to be

reusing throughout this course here so i

am going to go on a folder in my system

and i am going to right click on the

let's do this this is going to open this

folder in visual studio code and i am

going to trust this folder here be

careful what you trust because some

things are going to do some malicious

things on your computer make sure you

trust the folders that you open up so i

am going to trust myself because i am

the creator of this folder here and this

is going to open visual studio code

now in our install video we installed

the c plus plus extension for visual

studio code again if you don't have this

installed please make sure you go back

and install and make sure this is saying

that this is enabled and now we want to

use this to write c plus plus

applications here we're going to write a

simple toy c plus plus application to

just test that our compilers support c

plus plus 20 and then we're going to use

this as a starting point or as a

template project so i want you to click

and we're going to create a file called

and once you do that you will be able to

type c plus plus code in this year so we

are just starting out here i would

recommend to type this exactly as i do

here so we're going to say include and

say opening angle bracket and say io

and we're going to go down here and say

and we're going to go inside these curly

braces and say auto result and you are

going to exactly type what i tap here

don't worry we're going to have a chance

to learn about all these things here so

i am going to put a pair of parentheses

and i am going to say 10. and i am going

to put a weird operator here this is

called the spaceship operator it is just

something we can use to test that our

compiler supports it plus plus 20 and

we're going to put a 20 here and then

we're going to try and see if this is

greater than zero and we're going to

print this out we're going to say stdc

out again don't worry if you don't know

what this is this is just a way for us

to test and see if our compiler is going

to be able to use c plus plus 20. we're

and this is going to be our program now

we want to make sure we compile this

program so to bring in your compilers in

visual studio code all you have to do is

come to the terminal menu here so please

an option to configure tasks i want you

and once you do this you're going to see

that visual studio code is going to find

the compilers that we just installed you

gcc compiler we installed in mingw you

see that it has found the clan compiler

i know about the g plus plus compiler

because you can see the path here you

can see c major w ben g plus plus dot

exe this is where we installed our g

plus plus compiler and i know about the

clank compiler because that's what's

being found here for example on this

entry here you see it says cmajw bin

clan plus plus so we wanted to configure

these two compilers here and later

visual studio could use them to build

now what we're going to do is click on

the g plus plus compiler first

and when we do that this is going to

create a tasks that json file in our

project and you see that it has created

a folder called dot vs code if i click

on my main cpp file here and do reveal

this is going to open up on my system

and you see that this has created a dot

vs code folder and if we go and we're

going to find this tasks.json file this

is going to be our configuration to

configure which compilers that

visual studio code is using to compile

our main.cpp file here so if we go in

it's going to really have everything

ready for us so you're going to see that

it's going to be using our g plus plus

compiler this is the path to it and in

our args options here we have the

options that we pass to the compiler to

compile our program here now i want to

change this to say which kind of

so we're going to change the level here

g plus plus and say the version i think

that's going to be more descriptive here

so we're going to save world with g plus

11.2.0 because that's our version here

and the rest is really going to be

enough so let's try and see if we can

compile our program here and see the

the other thing we need to do because

this program is using c plus plus 20 we

need to configure our compiler to use c

plus plus 20. and one way to do that in

gcc and you can really search these

if we come to our search engine here and

say configure gcc to use c plus plus 20

and say c plus plus 20. you can search

these things and find information and it

is a really good way to test your things

so let's see if we can find a link to

help out we have a stack overflow link

here so we can crack this open and if we

go and we're going to find a batch of

things for example we can say std c plus

plus 20 here as an option to our

compiler and this is going to bring

c plus plus 20 support in our gcc

compiler so i am going to copy this

and i am going to come back in my visual

and i am going to pass a flag to boiled

in c plus 20 mode and it is something i

just got from stack overflow here and we

are going to pass this to our compiler

and put a comma to make this a valid

configuration file and i am going to

now once we have this open and we want

to build this we need to bring a

terminal window so we we're going to

bring the terminal window so that we can

see things happening and we do that by

coming to terminal and saying the new

and we will come back to terminal again

and say that we want to run a task in

this case we're going to be running our

world with gcc 1120 again if you are

using a newer version that's what you

should use and if we click on this thing

please make sure you have the main cpp

file selected before you do this so i

have this selected and i'm going to go

to run task and i am going to click on

this little thing you're going to see

that this is going to kick off the

and we're going to wait for this to

finish and you're going to see that it

is using c plus plus 20 here we're going

to see that the world finished

successfully and we have a main.exe file

created here so if we go in our terminal

in visual studio code and click enter

type clear and hit enter this is going

to clear the screen this is something

you can do to clear things out we can

run this main.exe binary directly here

so we're going to run exe here and if

you run it it's going to say zero and

this is an indication that we have our

visual studio code editor connected up

to our gcc compiler and we can use that

to compile c plus plus applications and

this is really the configuration with it

now you may ask how do i know this how

do i did i know the steps to follow to

well if you come to extension tab here

and before we even do that i want to

bring to your attention that we have a

bunch of tabs here in visual studio code

we have a tab that says file i think the

one here saying explorer we have a one

we can use for version control if you

use something like git or whatever you

can use this but in this course we're

mostly going to be using the explorer

extensions tab to install things and at

a later time i will show you how to use

the debug tab here or run a debug tab

but in most cases we're going to be

using the explorer tab or the extensions

tab here if you want you can click on

this to close this so that you have some

more space you can click again to bring

this back these are some things you can

do in visual studio code but i am going

to show you how to configure your

compilers where i got the information so

and we're going to find our cnc plus

if we scroll down we're going to find

tutorials on how to set up this on

different compilers for example you can

to see how to set up a visual studio

code to use your compiler from microsoft

if we come back we can see a link to see

how to use this with mingw on windows

and let's see what else we have we can

come back to here and we can see how to

use this with gcc on linux or clango on

a mac you can really choose whatever is

relevant for your operating system but

in this case here we are just using the

windows operating system so we're going

to see how to use this with the mingw

compiler that we just installed now we

can use the mingw compiler and i would

recommend reading up on this entire

thing to have an idea on what is

happening we already have our g plus

plus compiler so this is this command is

going to work again if we come back to

terminal here and run g plus plus

version i think we can see that we run

these commands here to see these things

working so we have this step here and if

you wonder what gdb is it is just a

debugger you can use to debug your

programs and again if we come to our

version we're going to have this

available from our mingw installation

you can see that we have this here so

this is working just fine you can really

follow this and configure your visual

studio code installation but i am just

showing you how to do this pretty fast

you can see that this is what we set up

in our configuration file which is our

tasks dot json file now one thing you

can do is modify the task.json file to

build every single file in your project

and this is something that is going to

make things easier what i'm going to do

is go back to our visual studio code

instance and find our project we're

going to crack open our tasks that json

file which is living in our dot vs code

and i am going to take out the craziness

i have in my arguments here i am going

to select everything i am going to

and i am going to put in a configuration

that i am using for my projects here to

make this super easy what this is doing

it is telling the compiler to build in c

plus plus 20 mode it is going to tell

visual studio it is going to tell the

compiler to build every single cpp file

in our project so if we have multiple

files they are going to be built

together and we're going to specify the

name for our output file for example if

we don't want our binary executable to

be named mainly.exe we can give it a

name and i am going to be naming mine

rooster.exe in the course here i would

recommend doing the same so that we can

the same habits as we go through the

course here but of course you are free

to use whatever you want in your c plus

plus programs here so once you have this

you can click save here and this is

going to save our json file here i can

and i am going to bring my terminal by

and the terminal here this is going to

bring back my terminal that i had before

and i am going to run the clear command

and i am going to do dir to show the

of my folder on windows here i wanted to

remove the main.exe file from the

terminal here so what i am going to do

and i am going to say the name of the

file i want to remove i am going to say

dot exe and if i hit enter notice what

is going to happen the file is going to

go away i don't see it anymore here i

want to build again using my new

configurations in my tasks the json file

i am going to run the task to build with

this is going to build again and you see

that it is using the configurations that

i passed you see that it is building

every single cpp file in the directory

here and it is going to generate a

program called rooster.exe and we if we

look here we're going to find it we can

and we can type clear to clear things

out and if we do the ir again we're

going to see that we have rooster.exe

rooster.exe here and this is going to do

what we want this is really all you need

to do to connect visual studio code to

your gcc compiler now we're going to

connect visual studio code to our clan

compiler that we have installed we

really want to be able to use it with

our project here and we're going to go

through the seven steps again so we're

going to go to terminal and say

and we're going to choose something that

says the clanger compiler and we're

going to find clang plus plus so let's

hunt for that i have something that says

cloneplusplus.exe i am going to click on

that and if i do this this is going to

tasks.json file so watch out for this i

and let's crack this test that json file

open and you're going to see that this

is going to also set up another

configuration to world using my clang

and again i can edit this out a little

bit to say what we want let's look at

the version of cloud we have installed

to say that out this is going to be 12

1 so we're going to say world with clank

12 0 1 let's say that here in our level

12.0.1 we can say that right here and

you see that it is really doing the same

thing we did with our gcc compiler so

what i can really do is still everything

i did in my gcc compiler i can

and i am going to take out the arguments

i have in my args here and i use what i

have in my gcc compiler you can see that

you can use the client compiler and the

gcc compiler in the same way and this is

something really cool so now we have the

option to use two compilers and this is

really cool so we're going to close the

json file and it's going to be saved

and we're going to bring up our terminal

and let's bring this up a little bit and

we're going to do dir on windows and

we're going to remove the binary again

we're going to remove roster.exe

and again what you can do you can start

typing the name of the file you want to

remove and hit tab if you do that the

terminal is going to autocomplete this

for you and this is really cool so if i

do this the file is going to go away you

see that it is going right here

and what i am going to do is world with

the clan compiler can do that by coming

to terminal i am going to say that i

want to run a task and i am going to be

given an option i can either build with

gcc so if i choose gcc here it's going

to be used but i can also use clan let's

use clang here so i'm going to click on

and you're going to see that visual

studio code is going to kick off the

this is going to build my binary

executable and notice that it is using c

plus plus 20 again the build is going to

finish successfully and i will have a

binary here and this is going to be all

i need to do so if i hit enter and run

and hitting tab this is going to

auto-complete if i run it it's going to

say zero and this is what we expect here

if you have some kind of error please

try and fix it if you have a problem you

can ask me and i will do the best i can

okay now we have our two compilers

working we need to configure the

compiler from microsoft now the compiler

from microsoft is a little bit weird

again you can read up on this by coming

to your extension documentation

and going to using the compiler from

microsoft with visual studio code on

windows you can read up on all this if

you want but i am just going to show you

a quick way to get this running so the

compiler from microsoft is special in

that you have to specify the path to it

for example if we open a regular

we're going to see that the terminal is

cl.exe compiler is not recognized and

the reason is we don't have the proper

environment variable settings for the

operating system to find this compiler

when we call it right here we are able

to use g plus plus and clan because we

put the environment variables in place

if you remember when we installed them

we did something like this we came to

the start menu and did env we came to

environment variables here and we put

to our compilers in our environment

variables here you can see them right

here so we don't have the same thing for

the compiler from microsoft and that's

for a reason because we may have

multiple compilers installed from

then if you have multiple compilers it

would be really cumbersome to choose

which compiler you want the guys at

microsoft opted for the option for you

the developer to specify which compiler

you want to run by coming to the start

menu here and typing developer

and choose which powershell for the

compiler you want to use for example if

we want to use the visual studio 2019

compiler we can click on this and then

the c plus plus compiler from microsoft

for example if we wait for this to be

we're going to see that we're going to

have a message saying that this is our

compiler we can use it however we want

so what we're going to do is set up a

terminal like this and use this terminal

to start visual studio code and the

visual studio code is going to start in

where it can find the compiler from

microsoft i know this is confusing but

please bear with me this is what we need

to do to get this to work if we start

visual studio code in a mode where it

knows about the environment variables

for the compiler from microsoft we will

have the ability to say cl.exe

and we will be able to use that right

here but you see that it is not

recognized now but we can use the g plus

we're going to see that it's available

we can use it we can use clan plus plus

and if we do version as well we're going

to see that we can use this little guy

here we also want the ability to use the

compiler from microsoft but to have

access to that we will have to close the

visual studio code instance we have here

and we're going to come back to our

project let's see if i can find it here

so we're going to go to the location

where we have our project and we're

going to change to the location of the

project here so i can grab the location

from my visual studio code project that

i just set up i am going to come back to

my powershell window that knows about

the path to the c plus plus compiler

from microsoft and i am going to change

it to the location of my project here so

i am going to say cd and paste in the

path i just copied and if i hit enter

this is going to change to my location

and i really recommend using powershell

if you have access to this because it is

a little more convenient to use it

supports more commands that you can use

in the command prompt but again that's

going to be your choice now i am in the

location for my project if i do ls or

you can see that i can see my main cpp

file can see the binary we generated

earlier but this is not problem so what

and i say a dot and this is going to

start visual studio code in the current

folder of our project year so if you hit

enter we're going to wait for visual

studio code to come up it is going to

come up with the project we had in that

starting visual studio code this way is

that it's going to know about the

compiler from microsoft if we come back

you're going to see that now it knows

about the compiler from microsoft and we

can use it to do things so let's set

this up again if you want you can read

on the documentation from visual studio

code itself but again i am going to show

you how to do this you can see that it

is really the same things they are doing

here so let's come back to visual studio

code and we're going to go to terminal

and we want to configure a task

now you see that we have the compiler

from microsoft available you can see

that we can use that right here so what

and this is going to add a new entry in

our configuration file and it is going

to open up if we go here we are going to

find that we have a command to build

using the compiler from microsoft so

let's change the level here and i say

world with msvc i think this is going to

be more descriptive and this is really

going to build your thing now i am going

to change this up so that it works

everything in the current folder

and again i am going to remove

configuration that i have ready on my

system here this is what i use for all

my projects again this is just calling

the compiler and giving it options to do

things we just need to specify that we

want to use the lattice standard of the

c plus plus standard and it is going to

the input files we're going to be

building everything in the current

folder this is what we are saying here

and the output file is going to be

if we save this by saying ctrl s or

and close our tasks dot json file we can

bring up our terminal window by going to

view and saying the terminal here

and we can go down and clear we can say

and if we do rm and say rooster and hit

tab this is going to remove the binary

we generated with the clang llvm

compiler earlier now we want to build

with the compiler from microsoft so

let's do this we're going to say

terminal and we're going to say that we

want to run a task but this time we want

to build with msvc this is what we want

to do here if we click on this little

thing we're going to kick off the

process to build with the compiler from

microsoft and we're going to wait for

and if we wait we're going to see that

the world finished successfully and if

we look in our folder we're going to see

that we have our output file and we can

come in our terminal and hit to enter

and do clear to clear things up and if

and hit enter you're going to see that

it's going to say zero and this is

confirmation that we are able to use our

visual studio code editor and be able to

use it with all kinds of crazy compilers

and this is really cool if you are on

windows i recommend setting this up

because it's it's going to make it

easier to run a c plus plus applications

state-of-the-art compilers like msvc

clone and gcc here and this is really

cool now we have everything we need to

start running c plus plus applications

but before i let you go let's show you

how you can set this up so that you have

an easier time with regards to

intellisense and whatever so what we're

going to do we're going to go to our

view menu and we're going to choose

and in this we're going to say c or c

we can say something like this and we're

going to choose edit configuration ui

this is going to give us an option to

and i want you to configure things your

let's see the options we have here i am

only going to have the option for win32

but if we go down we can specify

visual studio code configured for for

example it's going to give us

intellisense or autocomplete and all

kinds of greater things using the

setting we choose here if we want we can

choose the gcc compiler or whatever i am

just going to leave in the windows msvc

compiler because i am on windows here

but know that you can configure these

things now if we go down we're going to

see that we have the option to configure

the c plus plus standard and the

compiler path that is going to be used

to figure things out we're going to be

using the compiler from microsoft here

but know that you have the option to

choose any other compiler for example we

can choose the g plus plus compiler we

can choose the clank plus class compiler

you can configure these things and if

you need to change this please come back

here and do these configurations here

we're going to leave in this whole

intellisense and what we will do

is configure visual studio code to use

the c plus plus 20 standard so we're

here and if you set this up you're going

to see that visual studio code is going

file which is going to store all these

configurations here so it is really

a configuration for what we choose in

our configuration here so make sure you

choose what makes sense again i would

recommend using c plus plus 20 but if

you go on top you can really use any

compiler you want i am going to use the

compiler from microsoft this is okay i

configuration for intellisense here and

i am going to close this and we are

really ready to start using visual

studio code to ride c plus plus

application so let's clean this up a

little bit we're going to view our

terminal and we're going to remove the

junk that was generated by the compiler

from microsoft i am going to say rm and

and i can remove the binary i can say rm

and say rooster and say tab this is

going to autocomplete and really remove

things i don't need i am going to remove

the pdb file i am going to remove

you know i am going to remove the main

object file so let's say main dot obj

and i am going to remove main dot

or vc we don't want to remove our cpd

file so now we have a project we can use

as a starting point to write c and c

plus plus applications here so what we

will be doing in the next few lectures

or the next few chapters is reusing

this thing here as a template project so

c plus plus 20 template project and

let's do this here i think i need to

close video studio code otherwise it's

going to complain so i am going to call

this little guy c plus plus 20 template

later when we start learning about c

plus plus proper we're going to be using

this as a starting point and we want to

have to reconfigure the compilers our

the compilers that we set up here namely

the compiler from microsoft the g plus

plus compiler and the clang plus plus

compiler and that's going to be really

cool this is really all i have to share

in this lecture i hope you have visual

studio code set up to use all these

compilers we are going to stop here in

this lecture the next one we're going to

start and see how to set up your

development environment on linux and

we're going to start by installing

go ahead and finish up here and meet me

there in this lecture we're going to see

how to install c plus plus compilers on

linux we are going to be working on an

ubuntu 2004 system and we will install a

new version of gcc and the latest

version i can get my hands on for clang

llvm so let's do this okay so here i am

on my linux box this is ubuntu 2004 if i

we're going to see the information on

and you will have to adapt this for

whatever linux distribution you are on

and to install gcc it's really simple

but the problem is the latest version of

gcc at the time of recording this video

is gcc 11 and it's not available in the

ubuntu packages now for example if you

you're going to put in your password

you're going to see that this is really

not available yet right we cannot find

this so the best version we can install

is gcc 10 which i happen to have

installed already on this system so

we're going to do gcc 10 that's what

and if we do this we're going to see

that this is already available you can

also install g plus plus done i think

okay so we're going to run the command

here and we're also going to see that

it's already available here but if you

they are going to be installed and you

can use them on your linux system

another tool that is necessary on linux

is the gdb debugger so we're going to do

right if you install it it's going to be

installed but i already have it

installed already so now if i do gcc 10

on my system here and say version we're

going to see the version printed out we

can do g plus plus stand we can see the

version here let's do that for c plus

so we're going to see the version here

and it is going to show up let's wait

for this we're going to see my gdp

version here and now i can use these

compilers to compile c plus plus code on

my linux box here so this completes our

steps to install a gcc compiler on linux

we're going to look at how we can get a

on our linux box here and it is really

simple all you have to do is to do

and we're going to install clang 12

because that's the latest version at the

time of recording this video if we do

this we're going to see that it's going

to install i already have it installed

here but if you don't have it installed

it's going to install on your system and

this is going to give you all the tools

you need to compile with the clan

compiler on this particular ubuntu

system these installs are going to be

installed in my user bin directory so if

i see the there and do analysis to show

and scroll up we're going to find all

the versions for clan you see i have

multiple versions clang 10 11 12

and we have clan plus plus variance of

this i think we do okay we have clank

plus plus and clan here and this is

going to do what we want we have the

clan combiner and the gcc compiler

installed on our system here now if you

want to get the latest version of gcc

one easy way i found is to go through a

package manager called homebrew let's

right if you search for this you're

going to find it and if you want you can

and when you install it it's going to to

be basically there ready to use

and to install it i think there's a

command there install home brew

let's do this install here and if we do

we should find a link to install this

let's find a link i think they have a

link you can copy aha it is this little

thing here you can copy it paste it in

your terminal and it is going to install

and when you have home brew installed

you can go through it to install the

latest version of gcc for example if we

we're going to find all the information

to install this through home brew and

you just have to do bro install gcc and

this is going to install this on your

system and you're going to see that it

is going to install the latest version

at the time of recording this video so

this is what you should do for example

if we go back to our linux box we can do

let's cd into our home directory and

and it's going to tell me that it is

already installed because i installed

but if you don't have it installed it's

going to install it and you do this

after you have gone through the steps

the home brew package manager on your

system and you do that by just copying

this link and pasting that in your

terminal and hitting enter and it's

going to give you directions on what you

can do to get this properly installed on

your system here so this is really cool

so if you want the absolute latest

version in gcc this is one way you have

to get a hold of it without really going

through the complex steps to build the

compiler yourself on linux okay it is

taking some more time here i am just

going to kill this because i already

have the latest version of gcc here if i

do jcc 11 on linux and the do version

i am going to see that i have 11 2 and

it was installed through homebrew and if

you let this run to completion it's

going to install this on your computer

we don't have to wait for this so now we

have the latest version of gcc on an

ubuntu system we also have the latest

version of clan this completes our

tutorial on how to set up compilers on

linux we are going to stop here in this

lecture this one we're going to install

visual studio code on the linux system

and then in the next one we're going to

link visual studio code to these

compilers and be able to use visual

studio code type code and compile our

programs using these two compilers here

so go ahead and finish up here and meet

in this lecture we're going to see how

to install the visual studio code editor

on a linux system and again we will be

working on our ubuntu 2004 system here

so let's head over to the website for

visual studio code and download our

binary and install it on our linux

system here okay so here we are at the

website for visual studio code you can

get there by searching for visual studio

code in your search engine and you're

going to land here and all we really

is go down to find our download links

we're going to see that for debian and

ubuntu we can download here but you can

also find something specific to other

distribution okay so we are going to

grab the 64-bit version of debian ubuntu

here because that's my system and you're

going to find whatever makes sense for

your distribution so let's grab this

here we're going to grab the link so if

this is going to kick off the download

process and you will see this downloaded

on your system and once you have this

downloaded you're going to install it

and in ubuntu you can just double click

on this to install it or you can install

it like you install any debian package

on a linux system for example if you are

unsure on how to install debian packages

all you have to do is do a simple search

so let's do google.com and go there and

we're going to see how to install

2004 so this is our version here and

instructions on how to do this it's

going to be really simple so we can go

down and find a way to install so all

you have to do is says you do dpkga

say i and you pass the name of the

package and this is going to install

visual studio code on your system once

you do this you will have visual studio

code installed and you will be ready to

start it and use it on your system here

once it is installed you will have the

ability to come in your system here for

example and say code dot and this is

going to open a visual studio code

instance on your system let's wait for

this to come up so that you really see

okay so this is going to open visual

studio coordinate system and you can

start using it like we will do in the

next lecture okay once you have a visual

studio code installed and started up on

your linux system the very first thing

is to install the extension that is

going to allow you to do some c and c

plus plus and to do that you will come

to this tab here that says extension and

in our search box you can start typing c

and you are going to have an entry that

says microsoft here so please select

this and this is going to be the

extension you need to install you're

going to click on install and it is

and this is what enables a visual studio

code to do some c plus plus programming

and this is really cool if you want you

can check out how to use it on linux and

you're going to have instructions on how

to do this but we will do this in the

next lecture and show you how to

configure visual studio code to use the

compilers that we have installed in a

previous lecture so we're going to tell

visual studio code to use our client

compiler we're going to tell it to use

our gcc compiler and we will have the

flexibility to come to terminal and

choose which compiler we want to use and

we're going to do all this in the next

lecture so go ahead and finish up here

in this lecture we're going to configure

our visual studio code editor to use the

compilers that we just installed in a

few previous lectures so we will be able

to type our code in our visual studio

code editor just like we do here and we

will pass the code through the compiler

to generate a binary that can in turn

run on our linux system here this is

what we want to do so we want visual

studio code to use the compilers that we

installed so let's head over to our

linux box and do this okay here i am on

my linux box this is the current

directory where i am at this is where i

am going to do my things here so i am

going to create a folder and call it a

template project let's do this we're

mkdir and we're going to say c plus plus

20 template project i think this is

or we can even say cpp because i'm not

sure the plus signs here are not going

to give us a problem let's play it on

the safe side and we are going to create

this folder and we're going to cd into

okay once we are in this folder we're

going to open this folder in visual

studio code and the easiest way to do

once you have visual studio code

installed is just to type code and type

and you will basically be telling the

operating system to open visual studio

code in the current folder here so i am

and this is going to kick it open and i

trust this folder because i just created

it and we are in our project here the

very first thing we're going to do is to

create a main cpp file so let's do that

and i did that by clicking on the plus

and i typed in the name of the file and

i am going to put in some dummy code

here that we want to use our starter

iostream and we're going to put in our

code here we're going to say main and

again you don't have to type all this if

you want you can get the code from the

resource section on the lecture so you

can copy the code paste that in here and

be on your merry way because we haven't

really started learning about c plus

plus we are setting up the environment

so don't stress yourself here

this is just some simple code to test

our compilers to see if they support c

plus plus 20 because we want to use the

letter standard we can get our hands on

type exactly what i typed here so we're

and we're going to put this weird

operator and say 20 and we want to see

madness here is greater than zero this

is what we want to do and we're going to

say stdc out and the same result okay so

type exactly what i type here and as we

progress in the course we're going to

make sense of all these madness we see

here so now that we have a cpp file

containing the code for our c plus plus

program we want to compile this and we

need to tell visual studio code which

compiler it's going to use to compile

this program here to give us a binary

that we can run so what we're going to

and we're going to say that we want to

and the task is really a set of

instructions you give to visual studio

code on how to take your c plus plus

project and turn that into a binary that

can run on that system here so that's

what we want to do we want to tell

visual studio code which compiler it's

going to use we're going to configure

task here and you're going to see that

it's going to discover many compilers on

my system here you see we have clan 10

clang 11 clan 12 and we should also have

gcc 11 if we keep scrolling down we're

going to find these little guys here i

have many compilers on this system so i

which is installed through home brew

this is what i'm going to choose here

you say it's saying g plus plus 11 but

if you have access to g plus plus 10 you

can also use that it's going to work

with what we want to do in this course

here mostly so i am going to choose the

and this is going to set up an entry in

our tasks dot json file to build and run

this program here and that's what we're

going to do okay you see it is using

this particular compiler and one thing

we can do before we try and build this

we can change the level here to make it

more descriptive so we're going to save

and this is all we can save this

and we can close this json file and if

we bring up a terminal window we can do

that by hitting terminal here and

this is going to open up the current

location for example if we do pwd in

this terminal here let's use lowercase i

think that's what it wants we're going

to see the location here this is my

project so to build i can come to

and i choose run task and i am going to

choose the task to compile with my gcc

installation here if i choose this

it is going to kick off the weld process

and you're going to see that the

gibberish i have here is not supported

compiler is not configured to use the c

plus plus 20. so all we really need to

do is go back to our command and tell it

to use c plus plus 20. and we can do

that by passing a specific instruction

to the compiler to use c plus plus 20

like we do on line 10 here so we're

going to say std equals c plus plus 20.

we are going to save this a little bit

and i really wanted you to see this

problem here because many people are

going to forget this and we're going to

try and build again making sure we are

selecting the main cpp file here so

let's go to terminal run task and use

and wait for it to do its thing you're

going to see that the world now finished

and if we come back to our terminal here

and do ls we're going to see that we

and if we run it we should see a zero so

and if we run it we're going to see a

zero meaning that our program is running

and working correctly we are able to

compile a c plus plus project on a linux

system here now if you want to see how i

came up with the information to use the

tax json file please come back to the

and choose the c and c plus plus

extension we're going to click on this

and we're going to see all the

instructions on how to use this guy on

the linux system here so gcc on linux we

information here now you can read up on

all this if you want but what i am going

to do is go to visual studio code and

show you exactly what you need to do to

get this to work what i want to do in

there is set this up to compile

everything in my what i want to do is to

set what i really want to do is to what

i really wanted to do is to set this up

so that it compiles every single cpp

file in my directory here and i can do

a set of instructions i had prepared

so we're going to tell it to compile in

c plus plus 20 mode we're going to tell

it to compile every single cpp file in

this directory and then we're going to

specify the output file name for our

binary now this is code i used on

windows i need to adapt it to be

documentation there and we can

we can scroll down a little bit and

we're going to see that they use

backslashes here so that's what we're

going to use in visual video code to

play it safe so we can say this

a backslash and this is a backslash

and we will try and build this and we're

going to see what happens here this is

going to build our project in c plus

plus 20 mode we're going to be building

every single cpp file in the project and

the output will be called rooster this

is what we want to do here let's save

and i am going to close this json file

and i will bring up my terminal by

coming to view and save a terminal here

and i can remove the main.exe file or

the main executable i had in there if i

do lsuc it's gone but now if we try and

compile with the gcc compiler

we're going to see what happens you see

the world is good and we have a binary

called rooster and we can run it here if

we do rooster we're going to see it run

and give us a zero and this is really

all we need to do now we have this

our gcc compiler but we wanted the same

for a clanger compiler and we want the

flexibility to be able to switch

compilers by coming here and just

selecting the right task so let's do

this we're going to configure clan we're

going to come to terminal we want to

configure a task and we're going to

choose the best we have in terms of

clang that happens to be clang

plus plus 12 here so we're going to

choose this and this is going to add an

tasks.json file we're going to change

this to say that we want to build with

clan let's do that we're going to say

12.0.1 if i remember correctly but we

our terminal here let's go to terminal

and we're going to say clang plus plus

and 12 that's the version and we're

going to ask it what's your version it's

going to tell us in detail and if we

wait we're going to see this speed out

on the terminal here and this happens to

so that's what we're going to say in our

and uh this is really all all we need to

to build in c plus plus 20 mod exactly

what we did for gcc here so i am going

to copy this and put that in my

arguments here i'm i am going to take

out whatever i had in there i am going

to put in my new things and let's see if

this compiler works now we're going to

save our tasks.json file and come back

to the cpp file we're going to bring up

and remove rooster because we wanted to

build a new one with our clank compiler

and we will come to terminal run task

now we're going to choose to build with

clang 12.0 we're going to fix this in a

minute but if we do this we're going to

see that our weld process is going to

start it's going to be building with our

clan compiler it's going to be using c

plus plus 20. it's going to be building

every single cpp file in this location

here and the output of the world will be

a binary called rooster that we have

right here so the build is good if we do

ls we're going to find rooster and if we

run it it's going to say zero exactly as

we expect here and we have visual studio

code properly configured to use our two

compilers the client compiler and the

gcc compiler let's come back to our

configuration and change this to say

to be super clear on the version we have

we can close our json file here

and come and try to build again if we do

terminal and run task we will have our

compiler here ignore all these things i

think visual video code is going to give

you duplicates but you can choose

the version that says what you want and

it is going to work so we're going to

choose gcc oh we are saying gcc but we

want clang here so let's say that we

want to build with clan we're going to

12.0.0 this is right here so we're going

and it's going to build successfully and

we will have our binary here if we run

it is going to say zero and this is

really what we need to do here so this

is really all i had to share in this

lecture showing you how you can

visual studio code to compile using the

compilers that we have installed another

thing you can do to make your experience

better is come back to view and select

command palette here and you can do c

configurations through a user interface

and if we do this you're going to see

that this is going to create a cpp

properties json file so this is where we

what kind of intelligence what kind of

what kind of compiler is going to be

used we can do all these things here so

we're going to leave it to the default

it's on our linux system it's going to

be using gcc 11 which is the best we

but uh one thing you should note in this

course here is the c plus plus standard

we wanted to use so we wanted to use z

plus plus 20 and we want visual studio

format our main cpp file based on the c

plus plus 20 standard year that's what

we can achieve with this so once you

and if we go back to the main cpp file

that this is no longer flagged as a

problem with squiggly lines visual

studio code is properly understanding

what is happening here and this is

something you can do to make your

experience a little bit better

okay now that we have this project set

up and ready on linux we're going to be

reusing this as a template project every

time we start something new on linux so

every time we want to create a new

project we will grab this entire folder

so for example we will come to our

terminal here and go up a little bit

so cd and go up one level and if we do

ls we're going to have our c plus plus

20 template project we will copy it and

rename it to start a new project and

that's going to give us all the

configuration that we did we don't need

to reconfigure the compilers or whatever

it is going to work right out of the box

and that's really what we did here we

set up a template project that we will

be reusing all over again in the course

as we progress learning about c plus

plus 20. i am going to stop here in this

lecture the next one i am going to show

you how you can set up a development

environment on the mac os system

go ahead and finish up here and meet me

in this video i am going to show you how

to install c plus plus compiler on your

mac os system and we have a bunch of

options on the mac we can install the

gcc compiler we can install the clang

of the apple company or we can install

the clangle vm version all these are

options and i will show you how to

install these i don't have access to a

mac device so i won't really be able to

install xcode and show you but i think

you can manage if you are using a mac

system it is nothing complicated you

just have to go to the apple store and

click on xcode and it is going to

install for a gcc and clang llvm i will

show you how to do this using the

homebrew package manager which is also

going to make this super easy okay so

let's head over to our browser and we

have a good link here from digitalocean

on how to install and use homobrew on a

mac os system this is a really validated

link you can see that right here and you

can read up on this if you are using a

mac system i am going to share the link

here in the resources section of the

course and to use this we will go

through the mac os terminal and it is

nothing complicated you can search for

it and open it up and after you do this

you will have to install the tools

needed to build things on the mac os

system and that's going to install xcode

here so grab the command here and run it

in your terminal and this is going to

install everything you need and after

you have this installed you're going to

install home brew i do recommend coming

up to the website here for homebrew and

clicking on this copy icon here this is

going to copy the entire thing and you

and once you copy it it is going to give

and you can go in the terminal on your

mac os system i am using a linux

terminal here and then you're going to

paste this command in here and hit enter

once you do that you will be prompted to

put in the password it's going to tell

you that it needs to install homebrew

and you are basically going to wait for

this to finish i have to warn you this

is going to take some time even if you

have a good internet connection this is

going to take some time so be patient

here when it's done it's going to tell

you that it is finished and you will be

ready to install the gcc compiler and

the client llvm compiler through your

homebrew installation here i am not

going to click on this because

i already have this installed on my

linux system here let's go back to the

link and see what they say next so after

you paste that in it's going to install

and after that you will see that

homebrew is going to be installed on

you can use home brew to start

installing and upgrading packages you

can really read up on this but what i

is that you can use home brew to install

the gcc compiler and the clang ll vm

compiler so if we come to the search

broom we're going to find instructions

on how to install this so all you need

to do really is to say brew install gcc

this is going to install the latest

if we come here and say llvm or clank

we can find that right here llvm

and it is going to give us instructions

on how to install this and all you have

is brew install llvm and this is going

to install these two compilers on your

mac system so once you do that you will

have them stored somewhere let's go to

the install link and we're going to see

that homebrew is basically going to be

installed into things in your user local

directory on a mac device please tell me

if this is true for your case and if you

have a problem we'll try and go through

that and fix that up so if you are on a

mac i would really recommend going

through this to install homebrew once

you have that installed you will go

through that to install both of the llvm

compiler and the gcc compiler and that's

going to give you the latest versions

for these compilers to find out if they

will installed you can go in your user

local directory and you can hunt through

these compilers and you're going to find

binaries for them and start using them

to build your c plus plus applications

you okay so by now i am going to

consider that you have both gcc and a

clang installed on your mac system the

next logical thing to do is to want the

apple version of clang and i think

that's going to come as part of xcode

and it is going to come as a result of

running the command that we did before i

think it was this little command here

which is going to install everything you

ide so this is all i have to share in

this lecture again i apologize i don't

have access to a mac device but if you

have a problem you can tell me and i

will try to help you out and get this

we are going to stop here in this

lecture the next one we're going to see

how we can install xcode on your mac

device go ahead and finish up here

in this video i am going to show you how

to install the visual studio code editor

on your mac os system please know that

you can also use other ides like x code

or code lite do c plus plus development

but visual studio code is going to be

our main editor in this course here and

i would recommend to install it so that

we are doing consistent things that's

going to reduce chances for you to get

confused so we are going to head over to

the website for visual studio code

and to get there we can just type visual

studio code in here on in our search

engine and we will have a link here that

we can use to download our fans

so we are going to go down and find

download links for windows linux and mac

please use the mac download button here

and you're going to download the binary

and install it i think it is going to be

in the download folder by default so all

is drag that up in your installation

directory so that it becomes a runnable

application after you do that you're

going to run it and it is going to run

and you will have a user interface like

this with visual studio code opened up

once you have that up you will need to

install the c plus plus extension and

what you need to do is come to the

extensions tab here and type c and c

plus plus in here and you're going to

have an entry for microsoft click on

that and install this extension on your

system and your visual studio code

instance is going to be ready to handle

some c plus plus development and this is

really all i had to share in this

lecture showing you how you can get this

installed again i apologize i don't have

access to a mac device so i used my

linux box running inside window

subsystem for linux to show you this but

this is good enough i think if you have

a problem you can tell me and i will do

the best i can to help you out for now

we're going to stop here in this lecture

in the next one i will try and show you

how to set up a visual studio code to

use the compilers that we installed in

go ahead and finish up here and meet me

in this lecture i am going to try and

show you how to configure visual studio

code to use the compilers that we

installed on our mac system in a

previous lecture so we want visual

studio code to be able to pick up our

gcc compiler and use it we want it to

pick up our client compiler and use it

we also wanted to pick up our clanger

compiler from apple and use it to build

binaries that we can then run on our

system here so let's see how to do this

i have to say i don't own a mac device

so the best i can do here is describe

the process to you and if you have a

problem you can tell me i will do the

best i can to help you out okay so once

you have visual studio code installed

you're going to create a folder

somewhere and open visual studio code

from that folder and what you will

basically do is use the terminal to

navigate to a location you're going to

create a folder you can even call it cpp

template project you're going to hop

over into that folder and then open

visual studio code from that folder here

so for example we can hop over into cpp

and run code and say dot that's going to

open visual studio code in that folder

and from that folder you will create a

main cpp file by clicking on the plus

button here and you will create the cpp

file call it main cpp and you can put in

the content here and once you have this

the next task is going to be to set up a

compiler to build this little thing so

once you have this project you will come

to terminal i think there's going to be

a terminal menu somewhere and you will

choose configure tasks once you do that

visual studio code is smart enough to

scan your system and find any compiler

you have installed the first thing that

is likely to be found is the apple

client compiler so you're going to find

plus plus compiler so you can choose

that and you can use that for the apple

client compiler we are lucky we even

have a tutorial on how to do that so if

we click on our extensions tab here and

if we scroll down we're going to see a

link on using the client on mac os here

this is going to give us all the

instructions we need to use visual

studio code with the client compiler

from the apple company so if you scroll

down you're going to be able to read up

on all this but what i really want you

to see is the configuration file you're

going to see that it's going to be using

the clang compiler from the user bin

directory and this is mostly going to be

the clang version from the apple company

and sometimes you don't want this so if

you want to use the clang version that

we installed through home brew i think

you will need to go through the user

local directory because that's where

homebrew is going to put it you're going

to see that that's going to be the

location here from our tutorial and

you're going to hunt down for the clan

compiler and find your binary and that's

what we're going to be using next but

for the first time if you want to use

the clan compiler from apple this is the

configuration you need and all you need

to do in this case is change this to c

now once you have this configured you

will have the ability to come to

terminal let's show our files here you

will have the ability to come to

terminal and run task and choose the

compiler that's going to be the clang

compiler from apple but you can also

configure other compilers and all you

really have to do is choose them in the

list here and you're going to have a

json file to be exact let's show that up

and that's going to give you the

instructions you need to build this

and in most cases you will just need to

be careful about the path to the

compiler so for example if you are using

the gcc version you installed through

homo brew you're going to find that in

your location you're going to make sure

that's the correct one and you will put

in these instructions here to tell your

compiler to build every single cpp file

in the directory here this is what we do

if you use clan you're going to have

something like this and again i am

describing this to you because i don't

have a mac available to me right now

and if you have a problem you can tell

me we can try and sort this out okay and

by this time you will have the ability

to use your visual studio code instance

c plus plus programs using either the

apple client compiler the llvm glango

compiler or the gcc compiler and all

these are going to be compiling in c

plus plus 20 mode again to both you need

to make sure you have the file selected

and choose whatever compiler you want to

use for example if you want to use clone

12 from homebrew you're going to you're

going to select that and it is going to

be used to build your project and you

will have the ability to run your

projects just like we do here and it is

going to work let's make sure we are

running rooster here our binary

and it is going to run and printer 0 and

this is going to work again i am really

sorry i don't have a mac device

but this is what i have to work with now

if you have a problem on a mac device

please tell me i will do the best i can

in this lecture we're going to explore

the option to use online compilers if

for whatever reason we can't install a

radio compiler on our system and again

the goal is to be able to turn the code

we type into what looks like an ide

into a compiler and get a binary that we

can run and see the output of there are

a few online compilers that are very

popular within the c plus plus community

one box is one of them there is also

compiler explorer and kodiro but there

may be other ones out there if you do

research on your own we're going to go

to the browser and actually check each

of these out okay here we are in our

browser here i am on onebox.org

and you see that it really looks like an

ide inside we have the code we've been

running all along to make sure that it

compiles with c plus plus 20. on the

left here we have a few options we can

select which compiler we want to use you

see that there is a couple of gcc

you can see that this is a really nice

gcc versions you see we have clan 12

so if you want to test clang out you can

select it let's actually try this

so we're going to use clang head

so let's hit enter and see if clank 12

and you see that it really works clan

should support c plus plus 20 like this

gcc because that's what i like and you

can try putting different things in your

c plus plus code to see if the compiler

actually responds for example we can say

the message output here another good

thing with these online compilers is

that you can share this code and anybody

will be able to look at the code here

and run it so this is a really good way

get help from your instructor so i do

encourage you if you run into a problem

come and use one of these compilers and

send me the link the way you can send

the link you can hit on share here this

button here you're going to get the url

that you can copy and send to anybody

and they will be able to see your code

just like we're going to see here in a

minute okay you see that it isn't the

exact same thing and anybody on the

internet will be able to see your code

and try to find whatever the problem is

very fast one box is one compiler you

can play with the options that we have

load different libraries you see they

have a lot of boost libraries but this

is of no interest to us right now you

can play with it and see what you like

about it another one is kaliru which is

another online compiler you see it

doesn't have a lot of options like we

had in one box for example you cannot

change the compiler it's going to be

using g plus plus but if we hit compile

link and run it's going to run our code

and we're going to get the output here

again we can try and change this so that

you know i'm not lying to you so we can

std endl if you want you can hit control

plus on your browser and it's going to

and if we compile link and run

we should see the sky is blue in the

output window here this is really all

you can do with kolero and if you like

it you can donate to the developers i

think we have the same thing

on one box but it is in japanese so i

okay another one is compiler explorer

which is a really good one the main

purpose of this is really not giving you

the output it is actually seeing

assembly code that is generated for your

c plus plus code this is something a

little bit advanced for our purposes

here so we're going to ignore this we're

just going to be using it to test our

code with some of the popular compilers

if you look here on this drop box you

see that they also have a lot of

compilers you can use different gcc

compilers i think they have clan they

even have msvc how cool is this so you

can use a lot of compilers gcc clang you

see we have a lot of clan compilers we

11 here so this is a really good way to

try things out we're going to come back

and i noticed that i passed the flag of

c plus 20 to be able to support c plus

plus 20. again if i come here in my code

don't worry about these errors they're

going to go away in a minute

let's wait for the program to compile

you see that it is compiling let's wait

a minute the sky is white and everything

if you don't see this output here it is

possible that you didn't check this

checkbox run the compiled output

dropbox and make sure this is checked

and you should have a window like i have

here compiler explorer also allows you

to share your code with people on the

let me see if i can find the option to

you come to this drop box and you get a

and open a private window in my browser

here so that we know that it is some

browser that is going to be opening this

link and getting access to the same code

we have in compiler explorer and this is

and you see that we get compiler

explorer privacy we're going to close

and you see that we have the same code

we can try modifying this code for

example we can take out this third line

here it's going to start compiling you

see that it is compiling and it is going

to give us the output that we expect

from this so this is a really good tool

to try out if you want to share your

code with some people that are not close

to you this is a really good way to do

this it is also good to try out

different compilers for example if you

don't have a gcc compiler you can try it

out here and see if it does things for

example we didn't install clang on our

system but we can try it out and see if

it runs or could but make sure you pass

the correct flats here because you are

responsible for this if you pass the

you're going to get arrows for example

and oh and recognize command line option

std hello but if we say c plus plus 20

it is going to work so make sure you

in this lecture you're going to write

your first c plus 20 program and we're

going to start and attempt to understand

our program let's hop over to visual

studio code and actually do that the

first thing we want to do is to set up

our code so that we can open that in

visual studio code we're going to start

from our c plus 20 template project that

and i'm going to be doing the projects

for this chapter in this folder here so

we're going to do our very first c plus

plus program so what we're going to do

is go inside our c plus plus 20 template

and i noticed that we actually left in

the boiled files we don't want so

what we're going to do is remove this

and that this vc 140 fan we don't want

the main cpp file and the dot vs code

folder we're going to copy these things

and we're going to put them in our first

and we're going to open this folder in

visual studio code visual studio code is

not opened up you see that i have my

developer powershell opened if you want

you can open visual studio code directly

without going through this if you're not

going to be using the visual studio

compiler but i want to have the option

to use that compiler so this is how i am

going to open my visual studio code

to open this up i'm going to hit enter

and visual studio code is going to open

and it is going to open whatever we did

in the last lecture we don't want this

project because this is a template

project from the last chapter we're

going to close this folder go to file

close folder and we're going to open the

new folder we want to work on we're

going to go to file and hit open folder

we're going to go to the location where

our project is so you're going to go

where yours is i'm going to browse to

and i'm going to go in the current

chapter and choose 3 2 first c plus plus

it's going to open up and you're going

the last template project are still

valid here they were copied over if we

open the main cpp file it's going to be

the main thing we had in the last

we have the option to run task you're

going to see that we have two compilers

available and this is really good we are

ready to start using this let's try and

and we're going to have our binary

we can click in the terminal here

and if we want to open the terminal

again we have the option to come in

terminal and new terminal this is going

to open this up if we do dir in the

we're going to see our program generated

we can remove this thing here and say rm

dot exe and remove this we can clear

and we have a clean project we can start

learning from okay now we have the

project and it is building successfully

let's try to understand the code we have

in here the first statement we have it

this is a feature c plus plus offers to

load the pro built libraries that we can

use iostream is specifically going to

help us print thanks to the console

we've seen that we can for example print

let's take out all these things in here

and say std column column c out

this is coming from i iostream and we're

going to put two less than symbols we're

going to open two quotes and inside

we're going to type hello world

and we're going to go outside the quotes

and do two less than signs and say std

and put a semicolon this is going to

print things on the console if we run

so if we run this program the first

thing we need to do is to build this

program so we can come to terminal task

and we're going to build it with gcc and

after we've built it we can hit enter to

and we can do dirt to see the content of

the folder you see that a program has

been generated we can run it and if we

run it it's going to say hello world

this message is coming from this

statement here and we have this

statement because we have included io

stream to really make this super clear

we can try to remove this line that says

and the moment we do that you're going

to see that this tab says we have

you're going to see the message

namespace sdd has no member c out name

space std has no member a and dl

the z plus plus program doesn't know

what sddc out means because we don't

have the library included and you also

see that we have these squiggly lines to

make it really clear that we have a

problem so to really be able to use this

we have to include a third party library

that brings these features into our

program and that's what the include

statement here is really doing so let's

and we're going to say i o stream again

and let's wait and see that the problem

and the one thing you should really know

is that we don't have a semicolon at the

end of the io stream statement we don't

need to put it there but many c

plus plus statements need a semicolon at

okay i think this really makes it clear

what the include statement here is doing

the other thing we have in our program

this thing here is called the main

a function in c plus plus is a block of

code that does a lot of things

but the main function here is special

because it is the starting point of your

we also call the main function the entry

point of the c plus plus program and

what that means is that if you open the

program the main function is going to be

the very first thing that is going to

run and the things are going to be

executed in the main function in order

so the statement on the top is going to

run first and the statement after that

until we hit the end of the function so

this is what we mean here to really

drive this home we can come here in our

and say sdd engl and by the way this e n

d l statement is going to print a new

see it in effect in a moment let's

actually take it out so that we can see

its effect we're going to also do sddc

is to print number one and number two on

the terminal let's build this program

and if you want to build the default

task you can hit ctrl shift b for it to

happen very fast but i am always going

to come here so that it is really clear

what i am doing a program should be

generated now if we try to run it

rooster.exe and again we can hit

the app arrow button on our keyboard so

that's the last command that we run from

this terminal runs and this is going to

speed things up a little bit so if we

run this program it should say number

one and number two as you see here

but these two things are cramped on one

line and the reason is we are not

printing new line characters after we

print number one and number two and we

can solve this problem by putting in two

less than symbols and saying std column

this is going to put a new line

character after number one we can build

for our new changes to tech effect

after we do that we click on the

terminal hit enter we hit the app arrow

button if we run it's going to say

number one and number two on two

separate lines because we are printing a

new line character after number one i

really hope this makes sense

please do take some time to play with us

because if this is the first time you're

doing this some things might not be

clear and the best way to really make

sense of this is to type code run it and

see the effect of what you type by

running your program so let's do this a

couple of times we're going to do sdd

the statement for number two we're going

and we're going to do stdeandl

to really show the problem again we're

stdendl on the number two line

we are going to weld the build is going

we're going to click in the terminal hit

enter hit the app arrow button run the

program again and you're going to see

it's saying number one it's going on the

new line printing number two but we not

to jump into the new line from number

two so number two and number three are

going to be cramped on one line that's

what we see here we can solve this again

by putting in a new line after number

and uh this should solve the problem

again let's build we're going to run our

build task the build is going to be

successful we're going to hit the app

arrow to run the program if we run it

it's going to say number one number two

and number three and this is really good

now it should be clear that statements

in the main function are run in order

from top to bottom and that the program

is going to end when it hits the end of

this curly brace that includes our

function we're going to have a chance to

in detail later in the course but we are

just getting started and we need to

start somewhere so that's why we're

doing this main function thing here

another thing you can do is return from

the main function and in many examples

you will see people do return 0

and this is a way for the main function

to send the message to the operating

system if it's finished successfully or

if there was some kind of problem

we're not going to go into any more

details about the main function because

too much for now we are just getting

started we are trying to get a feel of

how c plus works the main message here

is really that you should be able to

print things to the console using sddc

out you should be able to print a new

using sdd ndl this stdc out and

stdendl thank come from the iostream

library that we are including here

if we don't include this library we're

going to have problems because

our surplus plus program is not going to

know where they are coming from so we

should really put this in if we want to

and we can return from a function to let

the system know the operating system

if the program finished up successfully

or if there was some kind of problem and

again this project is using the

and this is really all we set out to do

in this lecture trying to make sense of

the main function in c plus plus to

really practice these things i would

challenge you to write a c plus plus

program just like this that is going to

print your name 10 times try to do that

and if you have a problem please do ask

me and i will do the best i can to help

this is really all we set out to do in

this lecture i hope you found it

interesting we're going to stop here in

this lecture in the next one we're going

to start and learn about comments in c

plus plus go ahead and finish up here

in this lecture we're going to learn

about comments and c plus plus

comments are the way to put some

messages in your c plus plus chord that

are really meant to be read by humans

and one way we have to do comments in c

plus plus is through this backslash

backslash thing we have here this is

going to comment out the line so the

compiler is really not going to care

about it it's going to think that it is

something that is meant for the

developer to see so this is a one line

comment and this is how you do it in c

plus plus you can also comment out a

block of code in your c plus bus code

and this is something that comes in

quite handy many times you put your

comment in a backslash star and a star

backslash like this this is going to

comment things out in your code and the

compiler is really not going to care

about this let's hop over to visual

studio code and actually play with us so

here we are in the folder that is going

to contain our code the first thing i'm

going to do is go through the template

project i'm going to copy my files

and i'm going to go up again and we're

going to be learning about comments so

i'm going to put this in the folder on

comments i am going to close whatever

folder we have opened in visual studio

code and i'm going to browse to the

location where my project on comment

my project is in this folder that is

named three three comments i'm going to

open the folder and if i open the main

cpp file i'm going to find the starter

project we're going to remove this const

eval thank because we're really not

ready to understand this yet it was in

test that our compilers support c plus

plus 20. so we're going to remove this

and we're going to put in a message that

says hello world you already know how to

do that from the last lecture so we're

hello world and we're going to say

stdendl and don't forget this semicolon

at the end if you do you're going to

have problems so make sure your code

looks like this try to build it to make

sure it's working fine this is going to

run the gcc tasked world we can click on

the terminal here and it's going to

and we can open a new terminal here if

we want if we do dir we're going to find

our rooster program inside we can run it

and it's going to say hello world we

already know to do this from the last

lecture and in this one we are going to

be learning about comments the first

thing you can do is use slash slash so

and uh let's put some message here this

branch and the iostream library this is

a nice message that is going to give

some more information about this

statement to whoever might be reading

this program and this is called a one

line comment you can really put this

wherever you want in your c plus plus

file we can go in the main function for

example and say this is going to print

hello world to the console or the

terminal we can really put this anywhere

we can even put it after the return

statement here and really put in

whatever piece of information we think

is going to make sense to wherever it's

going to be reading our program okay

this is how you do a line comment you

can also do comments across different

lines and the way you do that you put

slash star and go down and say star

slash like this and whatever is going to

be in the middle here is going to be a

comment this is usually called a block

comment you can put in whatever you want

so if you have a piece of text that you

would like to use as a comment in your

program this is one way you can do this

one thing you should know though is that

you cannot nest these things but before

we do that let's try to build our

program to really show that there is no

problem if we have these comments in the

world is successful and if we click on

and hit clear to clear things out in the

terminal we can try to run our rooster

program and it's going to say hello

world you see that all these green lines

which are comments are really not

affecting the program all the compiler

is going to care about is this include

thing it's going to care about the main

function here it's going to ignore these

green things it's going to be like these

green lines that are our comments are

not in there this is the effect comments

have in your program and we're going to

be using this a lot in this course

one thing you should know though is that

you cannot nest these block comments so

if you try to do something like this

and uh say this is one comment and uh

come again and say this is another

comment you see that we have problems

already nesting is not allowed you're

going to get a compiler error and we're

going to learn more about these errors

in the next lecture but don't do this

don't nest these block comments if you

do that you're going to get some

confusing errors and this is going to be

the cause for them so don't nest your

blog comments it's going to give you

headaches okay this is really all we set

out to do in this lecture learning about

comments in c plus plus you can do one

line comments on a single line like this

you can do block comments to comment out

a block of text you can't nest your blog

comments because that's going to give

you a lot of problems you don't want

that and really use comments wisely and

don't overdo it because it's going to

turn your program into a novel and i

don't think people want that so use this

feature when you need it to give some

more information about your code and

don't overdo this we are going to stop

here in this lecture the next one we're

going to learn about different kinds of

errors and warnings you can see in your

go ahead and finish up here and meet me

there in this lecture we're going to

learn about errors and warnings in your

c plus plus programs there are three

kinds of errors or warnings you can get

you can get compile time errors you can

get runtime errors and you can get

warnings but what is really meant by

these things remember the ultimate goal

of every developer or every c plus plus

developer in our case here is to be able

to generate a binary executable file

from the c plus plus code and we have to

run the code through the compiler to be

able to do that and one thing you should

know is that there is a set of

that the compiler enforces on our code

successfully and those requirements are

the rules really that we have to follow

in our c plus plus program and if we

break those rules we're going to get

problems and these problems are going to

come in the form of compile time errors

let's look at compile time errors in

here we have a simple c plus plus

program that has a few problems we have

forgotten to put the semicolon at the

end of our stdc out statement here and

the compiler is going to freak out

if we compile this program we're going

to get a bunch of errors and the ide is

going to show us this problem some ides

are going to give you different errors

for example here i was using codelite

error expected semicolon before return

or something like this so this is a

compiler error and if you have this kind

of errors your program is not going to

compile compilation is going to fail

you're going to get this error and

you're not going to get your binary

executable and when you have this you

basically have to go back and fix this

problem compile again and when you get

rid of these problems the compilation is

going to succeed this is what a compile

time error is another thing you can have

is the run time error this is not going

to cause a compile time error the

compilation is going to succeed but when

you run the program it's not going to do

what you intended it to do in the first

place for example you may want it to

print green on some user interface it's

going to print gray or whatever it's

really not going to do what you want so

it's a logical error that you have in

your program and you have to fix it to

get rid of this and another thing you

should know is that sometimes these run

time errors can cause your program to

fail and terminate immediately and we

say that the program has crashed we're

going to see an example of this in a

minute the last kind of problem you can

have in your program is a warning

this is a problem that is not serious

enough for the compiler to halt your

compilation compilation is going to

succeed but this is basically the

compiler telling you you are doing

something that has some problems and you

should really fix it before it becomes a

serious problem so that's going to be a

warning for example here you see some

compilers can warn you when you divide

stuff by zero and we're going to see how

this works the main message in this

lecture is that you may have problems in

your program and they are going to come

in three forms some are going to be

compile time errors some are going to be

run time errors some are going to be

warnings we are going to hop over to

visual studio code and actually play

with this okay here i am in visual

studio code the first thing i'm going to

the template project we're going to be

using in our project here the project is

going to leave in this folder errors and

warnings i am going to copy over the

files and i am going to go in the

current project we're going to be

working on and i am going to open this

folder in visual studio code i am going

to go to file close folder i am going to

close this one and i am going to open

our new project i am going to browse to

it the project is this one i am going to

select it and select folder and it is

going to open up in visual studio code i

am going to close this welcome screen

and open our main cpp file we are going

to get rid of this constable fan this is

thing we had and we don't really need it

now we're going to get there in due time

what we want to see is compile time

errors we're going to put in our stdc

we're going to end this stdndm and we're

remove the semicolon on purpose and if

we try to compile our program like this

we're going to get a compile time error

this is what we want to see so let's try

and build our program we're going to run

the task to build with gcc and you see

that the world fails we're going to get

a bunch of errors in our terminal it's

going to say in function it main

expected a semicolon before return it's

going to try its best to tell you what

the problem is but sometimes these

errors can be really confusing in this

case it is really easy because we

introduced this error on purpose so

we're going to fix it in a minute but

before we do that i want you to see

these problems tab it is where the

problems are going to show up in visual

studio code so you should see your

problems in here or through the terminal

here okay one thing you should know is

that when you have a compiler arrow

compilation is not going to succeed and

you're not going to have your binary

file which is what you really want so to

fix this problem we're going to put in

our semicolon here we're going to build

again we're going to go to terminal run

task we're going to build with gcc and

this time you're going to see that

compilation is going to succeed and we

have our program here we can run it

through the terminal here so we're going

to click the terminal is going to go

and if we do dur we're going to see our

files in here and we can run our program

we can say rooster and if we run we're

going to have hello world so i hope this

really makes it very clear what a

compile time error as so this is one

kind of error you can get the other one

is around time error and this comes in

the form of things that don't work as

you really expected so let's say we are

trying to do some computation in our

try to take 7 and divide this by 0 for

example and this is a statement there is

a load in c plus plus so let's try and

build this and see what we get because

this is a common scenario where we have

run time errors we're going to run the

task to build with gcc okay if we do

this you see that world finished with

warnings we didn't get a compile time

arrow and our build was successful so to

really prove this i'm going to

go back in our directory i'm going to do

dur you're going to see that rooster is

there i'm going to remove it i'm going

rooster.exe this is how we remove stuff

from the command line when i do this and

executable file should be gone so let's

try and build with this statement and

and you're going to see that we get a

warning and not a compile time error

like we had here so we're going to go to

terminal run task we're going to build

with gcc and you're going to see that

we're going to have our executable here

but we had a warning and it's saying

that division by 0 was detected in our

program and it is a recipe for disaster

so why is it a disaster let's try and

run this program so we're going to

dirt to prove it's here and we're going

to run it if we run it it's going to say

hello world and it's going to end let's

try and actually use our own terminal to

see if we have a better chance of seeing

the problem here so i'm going to reveal

in explorer by clicking on main cpp and

i am going to try and open a terminal

window here powershell that we open

ourselves we've done this before

this shouldn't be new to you by now

so we're going to do dirt in here

and we're going to try and run the

program and it's going to run so so it's

not really giving us a run time error

here because we're not capturing this or

trying to use the result of this

division here we're just doing the

division which is a problem so let's try

and capture this we haven't learned

about variables yet but what we're going

to do now is do end value and we're

going to assign the result of this

division to this value and let's try

printing the result of dividing a number

by zero so we're going to do stdc out

and we're going to say value and this is

how you can print a value out on the

console okay now that we have this and

let's try and weld we're going to run

tasks and worldwide gcc we're going to

get the same warning but if we try to

run the program we're not going to get

what we expect let's run rooster exe we

expect it to say hello world and printed

the value but you see that it's really

struggling to print the value and it

gave up and ended immediately so this is

one example of a runtime error that you

can face in your program there are many

other kinds that we're going to see as

here we are just trying to raise your

awareness on these problems so that you

can know how to fix them when they come

up okay so this is all i can share with

you now about runtime errors we also had

a chance to see that this is also going

to give you a warning and a visual

studio code here is also helping out

telling us that we may have a problem

it's turning the main cpp file yellow

and it's saying that there is one

problem in this file and if you go here

you're going to see that we have a

warning here okay so this is one way you

have to see this so this is not

recommended to do so we're going to

comment this out okay this is really all

i had to share in this lecture we had a

chance to look at compile time errors we

also had a chance to look at warnings

and run time errors using this example

if you get a warning it is a message the

compiler is giving you that you should

really look it up and fix the problem

before it becomes more serious compile

time errors are going to cause your

compilation to fail and that's a really

good thing because the compiler is going

to stop you from generating a binary

that doesn't really do what you expect

it to do so that's a good thing but

sometimes the compiler want to give you

a compile arrow and you have a chance to

run into a runtime error and that's

really bad so be careful about these

things and when you have problems visual

studio code is going to show you the

problem in terminal or in this problems

tab and you're going to be able to fix

it up we're going to stop here in this

lecture in the next one we're going to

learn a little more about statements and

functions go ahead and finish up here

and meet me there in this lecture we're

going to learn about a little more about

statements and functions in c plus plus

computation in c plus plus you can say

that it is the smallest thing your cpu

can execute in your program every c plus

plus program is a collection of

statements so you're going to have a

bunch of statements that are organized

in a certain way to achieve whatever it

is you want and statements in c plus

plus must end with the semicolon we saw

in the last lecture that not putting

that semicolon is going to result in a

compile time error here is a basic

sample c plus plus program that we're

going to use to learn about statements

in the main function here we have two

variables declared we haven't really

learned about variables but they are a

way to store data in your program and

here we are storing two decimal numbers

one is called first number the second is

called second number we can do something

with these variables that we have in our

program for example we can add them to

have another variable in our program and

we can print that so you see here we are

saying stdc out the sum of two numbers

is sum so this is going to print 21

because it's going to add 12 and 9 and

the result of that is going to be

displayed on the terminal if we run this

program what i really want you to notice

is that this and first the number equals

12 thing is a statement in c plus plus

so it must end with a semicolon the line

here with second number is also a

statement so it must end with a

semicolon every single line we have here

in the main function is really a

statement and it must end with a

semicolon if we don't put the semicolon

in place we're going to get a compiler

error okay one other thing that is

really important to keep in mind is that

statements are executed in order in your

program and the order is from top to

bottom if you go back to our program

here so the first statement is the one

with first number here 12 is going to be

installed in memory when this statement

is executed by your computer and we're

going to go to the second statement with

second number and we're going to keep

going until we hit the end of the main

function and the return statement is

going to execute and when the main

function returns or terminates we're

going to get the return value sent to

your operating system and it's going to

know if your program ended successfully

or with a problem and the operating

system is going to know what to do with

that information execution keeps going

until we hit the end of the program or

if there is any other condition causing

for the program to terminate and we're

going to have more details about these

things later i just want you to know

that the statements are executed in

order in your main function another

concept i really want you to have an

idea about is the concept of functions a

function is really like a machine you

give it input and it's going to give you

output if we look at the operation here

to add first a number to second number

we can consider first number and second

number as input to the function and sum

is the output of the function we can

visualize that like this so we have a

first number and the second number we

pass that into our machine which is

really a function and we're going to get

the result of this function in a return

value or something that we get out of

the function as our result c plus plus

has a special syntax we use to define

functions this is our function to add

numbers on the left we have an integer

which is code name for a whole number in

c plus plus it's a number without

decimal points and it's a whole number

after that we have the name of the

function and we can name it whatever we

want and after that we're going to have

the list of parameters that we can pass

to the function and this is going to

work as the input to the function

after you do that you're going to have a

pair of curly braces the one is here the

other is here to the end and within

those curly braces it's going to be the

body of the function inside the function

you see that we are declaring a variable

and we are storing the sum of first

number and second number in this

and we are making this function return

the sum as the result and we're going to

be able to capture it if we call this

function in a function like me you're

going to see how this works in a minute

a function must be defined before it's

used so you can't really call a function

you haven't defined first in your c plus

plus program and here is a slightly

complete program to really put all these

ideas together we have our function to

add numbers it takes two numbers first

number and second number it's going to

add them up and store the results and

we're going to return some to be used by

whoever called this function and if you

look in our main program we have a

statement here we're going to store the

result of add numbers in the sum

variable and we pass first number and

second number in the function and we're

going to have that result stored in here

here we also call the function with

direct numbers you see that we pass in

34 and the seven and we're going to

print out the result here this is the

basic idea i want you to have about

functions they are reusable pieces of

code that group together a bunch of

statements to do whatever it is we

wanted to do in that function one

benefit about functions is that we can

reuse the code here if you look here we

are calling this function multiple times

without really rewriting these

statements that are inside the function

i know some of these concepts might be

cryptic to you right now we are going to

go to visual studio code and try this in

code and you're going to see exactly how

this works okay here we are in our

folder where we are storing our projects

i am going to grab the code from the

template project i am going to put that

in the current project which is

statements and functions i'm going to

paste that in here and i am going to

open this up in visual studio code i am

going to close the project we have right

now and i am going to open our new

project let's browse to its location i

am going to open the project on

statements and functions let's open this

folder in visual studio code and we're

going to have our starter project here i

am going to take out whatever we have in

the main function and take out this

contival thing we don't really need it

and we are going to try and define two

variables using two statements we are

going to say and first number and we're

going to put in a value let's say three

and we have to remember to end this with

a semicolon so this makes our statement

we can encode this in a comment to make

this pretty clear we're going to also

define a second variable so we're going

mean that it is a whole number it

doesn't have decimal points like 2.5 it

is a whole number like one or seven or

ten so we're going to say second number

we can give it a name and uh let's put

in a seven we're going to store these

values in our program and we can print

these values out let's print them out

first so we're going to say stdc out we

already know how to do that and we can

say first number and we can change these

output statements and say the first

number is first number you can do that

std endl and you can notice that visual

studio code is really helping out in

auto completing things we have in our

program let's print the second number to

really practice this so if we do std

you're going to see that it's going to

give us a bunch of options we can choose

from if you want you can scroll through

this with your mouse or you can just

type whatever you want to type so i am

going to do c out and it's going to try

and help out if i really want i can come

on c out here and click on it and it's

going to be auto completed which is

pretty cool so we're going to say second

number and we're going to say second

number here and it's going to auto

endl and we can try and compile this

program before we do i want you to guess

what we're going to get when we run this

program give it a guess we are then

going to go to terminal run task and

we're going to build this with gcc the

world is going to be successful we're

going to open this in our terminal the

terminal goes away no problem we're

going to open it again and we are going

to go in our folder and do the ir and

you're going to see that we have

rooster.exe our program we can run it

and it's going to say first number three

and second number s7 this is what we

have stored in these variables and the

benefit of storing your data in

variables is that you can change the

variables and let the rest of your

program really do the same things and

pick up the data that you have in those

variables for example we can put 13 in

and if we build again this number is

going to be picked up by this code and

we didn't need to go in and manually

change data in these sddc out statements

here let's weld so that we can see this

and we can close this by clicking and if

we run rooster again it's going to say

13 and 7. play with this a couple of

times until you really feel confident

and if you have any problem don't

hesitate to ask me i am going to do the

now that we have these numbers stored in

our program we can add them up let's say

and some we're going to declare another

variable and we're going to say it's

equal to first number plus second number

and we're going to end this with a

semicolon and we're going to print the

let's do sddc out and we're going to say

the sum is sum we're going to print our

variable here and we're going to print a

new line character with std endl we're

going to build our program so that our

changes are reflected in our binary here

so we're going to go to terminal

run task weld with gcc the build is

going to be successful we're going to

press any key we are going to click here

in the terminal and we're going to hit

enter and run rooster again and we

should see the sum and you see it says

the sum is 20 which is what we expect

now we are doing the sum here but it

would really be better if we're not

doing the sum in the main function here

what if we actually took this code and

wrapped it in a function that we could

reuse whatever we want we have seen how

we can declare a function so let's do

that we're going to follow the same

structure we saw in the slides earlier

so we're going to say and this is going

to be the return value or what we get

out of the function then we're going to

put in the name of the function we're

going to say add numbers and we're going

to pass in the parameters the parameters

can really have any name you want but

the type of the parameter first so the

parameters are also going to be whole

numbers like 1 5 7 or whatever you want

and we're going to say first program

and the second is going to also be a

whole number an integer and it's going

param okay after we do this we're going

to specify the body of the function

which is going to be between these curly

braces i am going to jump to the next

line so that this is really easy to see

so i am going to define our sum variable

inside the function it's going to be a

whole number and i can call it whatever

i want so let's call it result because

it's going to be the result of this

function and the result is going to be

the sum of first param and second param

okay i hope this makes sense and we're

going to end this with a semicolon

because every statement in c plus plus

has to end with the semicolon after we

we need to give it back to whoever

called this function and we're going to

do that with a return statement and

we're going to return the result to

might have called this function here now

that we have the function we can

actually use it we're going to go back

in our main function and what we're

is to reuse this sum variable and store

in whatever is returned from our

function the syntax for that is going to

and we're going to say equals and we're

going to say add numbers and we can pass

in whatever two numbers that we want to

we would expect this to give us 32

so if we print the sum again we can just

that prints the sum and reuse it here

let's align this a little bit and i want

you to take a guess at what we are going

to get from this program right now we

have these two numbers we are adding

them up if we get here this should print

the first number which is going to be a

13 so here we expect to get 13 and by

the time we hit this second number

statement we are going to print the

second number it's going to be 7. if we

get here we're going to print whatever

is stored in sum and in sum we have the

sum of first number and second number so

this should print 20 right and here we

are doing another sum of two numbers but

we are using a predefined function

that we have here before the main

function because you have to define the

function before you use it okay if we

add 25 and seven we are going to fall

into this function and it's going to add

those numbers up and we're going to get

and that's what we're going to return

and it is going to be saved in this

variable if we print it out it's going

to give us 32. i hope this makes sense

let's build and run our program run task

world with gcc the world is going to go

fine we're going to go back to our

terminal here that's clear so that

things don't disturb us and uh bring in

some confusion we're going to run our

rooster program and exactly what we have

here we have a 13 from the first

statement here we have a 7 from this

statement here we have a 20 from this

sum here which is here and we have a 32

that we got from this function the good

thing about functions is that we can

reuse them now that we know how to use

it we can use it again and we can say

add numbers and we can say 30 and

54 for example you add them up and

you're going to get the results so we're

going to print the result some and we're

going to put in the sum i really want

you to take some time and play with this

statement so that these things make

sense it's really not that difficult but

you just have to rock your brains around

how c plus plus defines these things so

we have this statement and we are adding

30 and 54 so it should get an 84 after

the 32 here let's weld we're going to

run the task to world with gcc we're

going to click on the terminal here and

hit enter let's clear so that we don't

have things disturbing us and we're

going to run our program and we have our

trusty 84 here i really hope this makes

sense and as a bonus i'm going to show

you that you can also call things

in the stdc out statement here without

having to store them in some predefined

variables and sometimes this comes in

handy so you can say std see out and

we're going to say sum and you might say

add numbers right in here and you're

going to say 3 for example and uh 42 and

this is going to give us a 45 that's

what we should expect to see after 84

so that's world and running the task to

build with gcc the world is going to be

successful we click on the terminal here

we hit enter so that we see our terminal

with output we're going to clear so that

we see our output without noise we're

going to run our program and we're going

to see a 45 here i really hope this

makes sense the whole point of this

lecture was to make you aware of

statements and function a statement is

the most basic unit in your c plus plus

program it basically lives on one line

but it can also spread across different

lines but we're not going to look at

that here maybe we're going to see that

later in the course statements are

executed in order so when our main

function gets to be run by the computer

it's going to go from the first

statement second statement third

statement and it's going to go until it

hits the end and we can see that here in

the order in which our numbers are

printed it is going from top to bottom

we have also seen that we can split our

code in different functions and wrap

whatever functionality we have in a

function we have seen the basic concepts

on functions a function has a return

value it has a name and you have to give

it the parameters and you put the body

of your function within these two curly

braces as an exercise i would challenge

you to do a function that multiplies two

numbers and call it in the main function

here to see the result if you have any

problem please do ask me i am going to

do the best i can to help you out this

covers all we set out to do in this

lecture and i hope you found it

interesting we're going to stop here in

this lecture in the next one we're going

to see how we can input and output

things from our c plus plus program go

ahead and finish up here and meet me

there in this lecture we're going to

learn about how we can get thanks in our

program and get things out of our

program and that's basically input and

output to and from our program we have

actually been doing this all along we

have been printing things from our

and with this technique you can really

as a highway that goes from your program

to the terminal you can basically think

of it like this data is going from your

program to sddc out and it's going from

here to the terminal and from this you

less than signs kind of point to the

left because data is going from your

program to htdc out and these two

symbols point to the left they point to

hddc out to signal to the fact that data

is going from here to here i really hope

this makes sense because sometimes these

things can confuse people this is the

reason why it's going from your data to

stdc out data is basically going from

your program into httc out and the sddc

out is one way we have to get data from

our program to the console there are

many others we have std c e r r or std

server this is what i'd like to call it

and what it does it prints errors to the

console we have stdc log which is going

to print log messages why do we have

these different things different

programs might decide to format these

messages differently because they are

different messages one is a simple

message from the program another is the

narrows you might want to turn this red

to really bring the attention

to this message because the user has to

solve that problem another might be a

log message that you want to store in

uses for these things differ and c plus

plus makes sure to give you different

ways to state your intent through the

tools that you use we have looked at

sddc out sddc error and stdc log what

does sd c i n do it does the reverse

it's going to take data out of the

program and bring that into the program

so let's look at a few examples using

these here we have an example of

printing data from the program to the

here we have a hello world message going

here we have a number going to c out

this is what we've been doing all along

we can also do a variable storing the

edge for example it's a whole number

so we print this out and the message is

going to go from the program to cl so

you can think that things are going from

the program to sddc out i really wanted

this to make sense okay if we go down

we're going to see that we can use cr to

print errors to the terminal and we

might say something went wrong or

something along these lines to bring the

attention to the problem and we can use

c log to print log messages and they

work the same way they all use the

stream output operator and it is going

to take data from the program to

the output stream really this is what we

mean here here is an example of how you

might read data and bring that into the

program here we have two variables one

is the age it's a whole number or an

integer and z plus plus and the other is

a string this is a type that allows you

to store strings in c plus plus we're

going to learn a little more about this

later but here i want to use it to

really make it clear that you can get

things from the outside and bring that

data in your program so we're going to

let the user type in the last name and

is getting data from the stream or from

the highway through which data comes

into our program and bringing that in

our program and here it should be clear

that the flow of data is in this

direction data is going from c i n and

we're storing that in a variable that we

have in our program that is called name

we do the same thing and ask the user to

print the age and they are going to

print that and the data is going to come

from cin and we're going to store that

in our edge variable here after we

collect the data from the user we're

going to print that and we're going to

say hello we're going to print the name

and we're going to say they are whatever

years old this is what this program does

and i really hope it makes it clear

how data input works through streams in

surplus plus another thing we can do

sddcin is chaining input and we can use

this technique to grab data in one

statement look at the program down here

to really understand this we have the

same variables age and name we let the

user type in the last name and age

and we grab the data like this we first

grab the name after that we grab the age

and we're going to print the same things

input stream operators like this to grab

the data in one go and this may come in

before we try these things in visual

studio code i want to bring your

attention to a problem that you are

likely to come in contact with and that

is reading data with spaces what if the

with spaces for example you asked me to

type my name i'm not going to type

daniel i'm going to type daniel cafwaya

and your program is going to run into

problems c plus plus allows to solve

this problem using std get line and you

using this syntax you're going to pass

in the stream where the data is going to

go and you're going to pass in the

variable that is going to read the data

information stored correctly in your

program this might be not making sense

yet to you we're going to go to visual

studio code and play with us and i am

sure it is going to make sense okay here

we are in visual studio code and we have

our project where we're going to store

our files data imported output we're

going to copy code from our template

project and we're going to put the data

in and i am going to open this folder in

visual studio code so let's close

whatever we have now and i am going to

open my folder let's browse there i am

on this folder data input and output i

am going to select that and the project

is going to open up in visual studio

code i am going to jump to my main

function i am going to take out things

we don't need and the first thing we're

going to do is printing data we have

really done this so we're going to

practice this a little bit we can say

and we can say hello c plus plus 20 why

not and we're going to put an std

endl at the end and remember our

semicolon and here i want you to really

put in your head that data is going from

our program here to hddc out and sddc

out is going to dump that on the

terminal that's how this works you can

also do a variable let's say ant

age for example let's say 21 and end

this with the semicolon and we can also

print the h we can say sddc out

age this is going to be sent to the

and we're going to do sdd and dl to add

new line character at the end and we can

try and build this before the program

gets more complicated let's go to

terminal we're going to run the test

and if we hit enter on the terminal here

the terminal is going to go away we're

going to create a new one no big deal

and uh if we do dir we're going to find

our rooster program if we run it it's

going to say hello c plus 20 and the age

is going to be 21. we are successfully

taking data from our program and

printing that to the terminal this is

pretty cool and you can think of sddc

out as the highway that is really going

to take your data from your program and

bring that to sddc out like this

we're also going to take the age it's

going to go through sddc out and it's

going to show up here you can think of

this like this okay now that we have

used sddc out we can use sddcr and sddc

log in the same way so we're going to

i'm going to say error message and the

message is going to be something is

wrong you may do whatever you want in

here and we have to remember to put a

new line character otherwise data is

going to be cramped on one line we can

also use sddc log it really works the

same way c log and we can say log

message and we're going to say something

and we remember to put std endl and our

semicolon if we build this program you

might guess what it's going to do it's

going to print these things on the

to terminal programs that support

features to format different messages

directly the program is going to know

that one message is a simple message the

other is an arrow the other is a log

but before we do that let's clear so

that we don't have noise here we're

going to run the program and it's going

to say the error message and the log

message here okay now what we're going

to look at is how we can get data into

our program and data is going to be

going in a different direction

it's going to be coming from the

terminal and flowing into our program

what we're going to do we're going to do

ant age one this is a new variable so

we're going to put in data and we're

going to bring in a string library to

allow our program to store strengths the

way we're going to do that we're going

strength this is how you do it in c plus

plus we haven't really learned about

this type it's a powerful type in c plus

plus but we will get it there when we

have more powerful tools to really

understand it we are just getting

started here so what we're going to do

we're going to say std strength and

and we're going to ask the user to print

their name and age you already know how

to do that so we're going to say please

type your name and age and we're going

to do stdndl on this and how we're going

to get data in the program we're going

stdcin and we're going to do std

cim and data is going to be going from

the stream to the program so the

stream input operator here points to the

and the data is going to be going in the

name variable because that's what

they're going to be typing in first

because that's what we told them to do

so we're going to store the name

stdcim data is going to be flowing from

sddcin into our h1 variable okay now

that the user has given us their

information we can greet them with a

personalized message we're going to say

stdc out hello and we're going to put

out their name and we're going to tell

them you are and we're going to put the

one because that's what they're going to

give us here and i'm going to say

and we're going to put an std endl here

i'm going to grab this and pull this to

the left so that we can see our entire

program here that's helpful so what we

are doing here we are getting data from

the user and we are storing that in our

variables and we are printing the

message so that the user can see it i

don't want the first things we did here

to disturb us when we world and try this

out so i am going to comment this out

and comment the first block of code out

using blog comments i think this is the

first time we use this and uh this is

going to be ignored by the compiler now

and it is only going to consider this

and this is going to be pretty cool

let's go down a little bit here and i

try to build the program we're going to

run the task that welds with gcc and uh

looks like the world is good we're going

to hit enter and we're going to clear so

that we are not disturbed by this we're

going to run the program let's say

it's going to ask me to type my name and

age my name is daniel i'm going to type

that hit enter it's going to want me to

and it's going to tell me hello daniel

you are 33 years old i put a slash here

we can try and run it again so that i

don't have to make that mistake again so

daniel that's my name i hit enter i say

it's going to say hello daniel you are

33 years old i really hope this brings

that takes data from the terminal into

your program so this is really what is

happening here when i type daniel it's

going to flow from the terminal and it's

going to go into my variable which is

name here and when i type the age it's

going to go in my edge variable here and

in here okay one other thing we can do

grab the data and put that in our

variables in one go so what we can do

here is comment this out and we're going

stdcin and we're going to put that in

name and we're going to change these two

things and put the other piece of data

in h1 if you run the program it's going

to work exactly the same way but we are

grabbing the data in one line so let's

weld to see this in action we're going

to run the task that worlds with gcc

we're going to click here and we're

going to clear if we run rooster it's

going to ask for the name and the age

i'm going to put in daniel and i'm going

to put my h and say 33 for example and

it's going to do exactly the same thing

but we have one compact line the last

thing i want to show you in this lecture

is how you can grab data with spaces

because if i try to put in data with

spaces here the program is going to fail

miserably let me show you this i'm going

to clear and i'm going to run rooster

again and i'm going to say daniel i'm

going to put in my full name and uh it's

really not grabbing the second name and

it didn't give me a chance to input my

so c plus plus provides a way to solve

this using std get line so let's see

what we are doing here and before we

play with this we're going to comment

out what we had here so that

it doesn't disturb us in what we are

about to do so let's come down here and

say that we were doing data input this

is helpful here and we're going to go

down and grab data with spaces so i am

going to set up another strength and

this is going to store my full name

that's what i'm going to say here and to

grab it i'm going to tell the user to

type in their full name and age so i am

going to sddc out so the way i'm going

to grab the data i'm going to do std get

line you see that we have this function

here and it's going to take an input

stream so asd dcin is going to work and

the second parameter is going to be the

variable where this string data is going

to be stored we're going to pass in our

full name and this is going to work just

fine and we're going to also grab the h

using the same technique we've used

stdcin and we're going to store that in

our h3 variable once we have the data we

can greet our user using the same

message we had before so i'm going to

copy that if i can do that and i'm going

to paste that here i'm going to bring

this to the same location it's going to

be full name here and it's going to say

h3 and let's try and weld we're going to

terminal run the task to bolt with gcc

and we have a problem because we forgot

our semicolon see how these problems

might come to you uh-huh so we're going

to put in our semicolon and another

thing i really want you to see

bring these things to the next line if

they turn out too long like we see here

so i can for example put this to the

next line and it is going to work just

fine so what i am going to do i'm going

to try and weld again run task to build

with gcc you see that the world is good

bring in our terminal i'm going to clear

so that we don't have noise here and

we're going to run our program it's

going to ask me to put in my full name

and it's going to want the age i'm going

to say 33 and it's going to reach me

hello daniel gaway you are 33 years old

we are able to bring data with spaces

into our program and this concludes what

we had to say in this lecture i hope it

made it very clear what these htd n and

stdc out things are they are basically

highways that take data out of your

program or bring data into your program

and the way you use them is what we've

done here in this course i would

encourage you to play with us a couple

of times if this is the first time

you're doing this we are going to stop

here in this lecture in the next one

we're going to try and recap on the c

plus plus development workflow go ahead

and finish up here and meet me there

in this lecture we're going to explore

the c plus plus execution model and show

you a simplified version of the memory

model of your c plus plus program here

is how our program looks it is a simple

program in our main function it is going

to call a simple function that is going

to add two numbers we have seen a

program like this before and when we

compile it it's going to be turned into

a binary this black icon here represents

the binary executable and it is not in

that you can read with your eyes if we

come back here to what we were doing in

the last lecture we can see our rooster

executable binary here if you try to

open it here you're going to see that

visual studio code is going to say the

file is not displayed in the editor

because it is either binary or uses an

unsupported text encoding so it says i

can't really say this because it's

binary and it says do you want to open

it anyway if i try to open it it's going

to be just some gibberish because this

read by programs it is not meant to be

by ides or text editors like visual

studio code so this is the binary file

we have here i tried to put a simplified

version of this program to represent

binary so that we can follow it up but

it is not in the form that is readable

by any human out there unless you are a

machine so why is it in binary because

binary format is easily understandable

by your cpu and we're going to see how

your program is loaded in memory and

executed statement by statement by the

cpu so that you can really understand

this so here is a representation of your

program here we have our how to drive

and we have the program sitting

somewhere on our hard drive in binary

format and it's waiting to be run by you

by double clicking on it or opening it

in the terminal and on the left here we

see a representation of the memory of

our computer and when i say memory i

mean random access memory i don't mean

memory on your hard drive this should be

really clear this is the random access

memory of your computer that is running

your programs very fast so when you

double click on our program or if we

open it in the terminal the binary file

is going to be loaded up in memory and

you see it in red here this is a

representation of that and it is ready

to be run by the cpu by the time the cpu

says in the memory location it's going

to know i have a program to run and the

cpu is going to start running it

statement by statement it is going to

start by the top so it's going to see

that it needs to allocate space to store

our integer a it's going to allocate to

that somewhere on the memory in yellow

here you see a and it's going to see

that it should store in a value of 10

and it's going to do that you can see

that here it's going to go to the next

statement and the next statement tells

a value b and it's going to store in f5

it's going to go to the next statement

it's a variable called c it's going to

allocate space for it but we didn't

specify a value for c so what it's going

to do is store in some junk value the

value in there is really unspecified at

the moment it's going to jump to the

next statement and what it's going to do

is print some things on the console and

it is going to do that it's going to

jump to the next statement and it is

going to print statement 2 and here it

is going to notice that it is going to

call a function i don't know if you have

noticed but the cpu has allocated a

special memory location for our function

the function doesn't leave with our code

here or anywhere near the variables that

we have here there might be a huge chunk

of memory between these two or three

things so the cpu knows that it is going

to jump to another location it's going

to ask itself if i jump to that location

to run this function how am i going to

come back and the cpu is smart enough to

store the return address and that's what

it's going to do it's going to say if i

go to that function i want to come back

to the address 6 and run whatever is

after this address so it's going to

store 6 and cpu memory and it's going to

jump to the function it's going to take

the first parameter as a and the second

parameter as b so a is done the

parameter 1 is going to be 10 it's going

to take parameter 2 it's going to be 5

because it is b here and in b we have a

5 and it is going to jump to the next

statement in the function and it is

going to add up parameter 1 and

parameter 2. after it adds those things

up it's going to return the result to c

we can see that here okay that's what

the cpu is going to do it's going to put

the results in c and the result is a 15

so we're going to write that in there

and now that the function is really done

it's going to come back to its address

and it is going to jump to the next

segment after that it is going to

print three statement three it is going

to jump through the next line and print

statement four it's going to do that and

by this time we have reached the end of

our program and it is going to be popped

off the memory and your program is

basically going to end this is how your

program is executed by your cpu and why

am i showing you this because it is

really good to have an idea of how

memory is allocated and used by your

program another good reason is that some

c plus plus feature require you to have

an understanding of a memory model like

this to understand how they work for

example you have seen that to call this

function the program had to jump from

address 6 to 30 and this is really heavy

especially if you are running a simple

function like we are doing here to add

two numbers so the cpu can realize that

and optimize this call to the function

to an inline function and add these two

numbers up right here at address six

without jumping to this address here and

this may come in handy and you need an

understanding of this memory model to

really understand these features this is

just one example i am giving you you are

going to reuse this model a lot in your

career as a class plus developer and i

thought it was a really good idea for

you to understand it firsthand this is

really all i had to share in this

lecture i hope you found it interesting

in the next one we're going to try and

understand the difference between three

key components of the c plus plus

programming language go ahead and finish

up here and meet me there in this

lecture i want to highlight the

differences between what we call a c

plus plus core language feature or a

standard library feature or an stl

feature because these are terms that

come up a lot if you happen to read some

documentation about c plus plus a core

feature is really a basic building block

that makes up the c plus plus

programming language you can think of it

for example how you define variables the

rules that govern how you can define and

use a function in c plus plus the rules

that say what you can do and not do with

the basic features of c plus plus that's

really what can be qualified as the core

feature of the c plus plus programming

language i don't know if that makes any

sense if we come back in visual studio

code we have a program we have used in

the last few lectures for example these

basic types that you use in c plus plus

the rules that define how you can define

a function for example if you put a

an angle bracket here and try to compile

this program it is not going to work

because we have violated the rules of

the c plus plus programs the basic rules

that define how the c plus plus

programming language works the basic

types that are defined in the c plus

plus programming language these little

things make up the raw ingredients you

use to make up a proper c plus plus

programs and these little row components

that you use to put together a c plus

plus program are called core features

think of them as the foundation on top

of which we really build daily use c

plus plus programs the standard library

highly specialized components that we

can easily use in our c plus plus

programs and again coming back to our

program in visual studio code iostream

here is a standard library feature

string here is a standard library thing

we have in the c plus plus programming

language and again the c plus plus

standard library tries to provide highly

specialized components that we can use

in regular c plus plus programs when you

use the c plus plus programming language

you don't really want to extend the c

plus plus programming language you want

to use it to build something of your own

and uh the standard library features are

things you use to work on your programs

very fast for example we have used sddc

out without really going into the

details of how the data is taken from

this program to the terminal that's

really advanced and probably complicated

but it is wrapped into this reusable

components and one of them is iostream

and we can use it relatively easily in

our c plus plus program okay i hope now

you have a better idea of what the c

plus plus standard library is now what

is the stl the stl is really part of the

c plus plus standard library but it is a

collection of container types think of

them as collections of things and we

have a set of types that allow us to

store collections we have algorithms or

functions that work on these collections

and we have specialized types that are

called iterators that allow us to

navigate through these containers

potentially running these algorithms on

each element in the collection this is

probably not making sense by now but you

can think of the stl as a highly

specialized part of the c plus plus

standard library and we're going to

learn about many features of these

things throughout the course but i want

you to have a basic understanding

between these three terms a core feature

of the c plus plus programming language

is standard library feature and the stl

and i really hope this is clear to you

by now in this chapter we're going to

learn about variables and data types

before we talk about variables and data

types i would like to take a moment and

and if you look at these cards many of

these things should make sense now you

know about the main function you know

that it is the entry point of your

program you know that your program is

going to be made up of statements and

statements and with a semicolon in c

you know about functions errors warnings

you now have an idea about how you can

handle input and output from your

program you can use comments you know

about the memory model and the execution

model that we talked about in the last

lecture you know quite a lot now we have

been using a program like this to do

things in the last chapter but there is

one thing that isn't really explained

yet and that is this ant this end is a

type that is predefined in c plus plus

and c plus plus predefines many types

here we have a couple of these types for

you to see as examples it is one of them

we have seen it a lot of times in the

last chapter it is used to represent

whole numbers like one two and three but

we have others for example double and

float are used to represent fractional

numbers numbers that have decimal points

for example 2.5 7.3 and numbers like

that and we're going to see the

difference between these two another one

that is commonly used is char or car and

it is used to represent characters in

memory and you can store in characters

like a b c and d and all the other

characters you can really put in we have

a bull which is a type that is going to

store two possible states the only

values you can really store in here are

true or false and we're going to see how

this works void is uh somewhat confusing

because it represents a typeless type

and it is really meaningful when we get

to talk about functions in detail so

we're going to learn more about the void

type a little later in the course we

also have the auto type which is really

not a type it is a keyword you use in c

plus plus to deduce other types and

we're going to see how this works later

in the course these are a few examples

of types we can use in c plus plus and

we are going to play with most of them

in this chapter another thing i really

want you to see is what does it mean to

really put a 4 in a variable in your

program everything you have in this

program here is represented by ones and

zeros in the computer's memory it really

looks like this it's a bunch of ones and

zeros in the ram of your computer and

there must be a technique to make sense

of this gibberish here and store data

that makes sense to humans and the

starting point is to group these ones

and zeros into little chunks that we can

manipulate each of these ones and zeros

is called a bet so this zero here is a

bit this one here is a bet and if we

group eight beats together they are

going to form what we call a byte okay

if it makes sense you can group your

bits in bytes or if it makes sense to

group them in groups of 16 you can do

that like we see here we're going to see

a little more details about this in the

next lecture okay here you see that if

you really want you can treat each bit

as a self-contained piece of data but

this is really not very useful but there

are some corner use cases for this okay

now we really have two sides on the

right we have data in the format that is

really convenient and understandable by

humans and on the left we have how data

is represented in memory so there must

be a way to transform between these two

forms of data because humans can't

really handle these ones and zeros well

and we do the transformation between

these two representations of data using

number systems we have a few number

systems available to us that we can use

binary octal hexadecimal are a few

examples and we're going to learn about

them starting in the next lecture so go

ahead and finish up here and meet me

there in this lecture we're going to

learn a little more about number systems

number systems allow us to transform

data from the form that is really

convenient for humans in a form that is

convenient for computers in these ones

and zeros that you see on the left we

can also use them to do the reverse go

from ones and zeros and go in the format

that is convenient to humans like this

22 or this steve name here to make sense

of how these number systems work let's

analyze the decimal system that we

really use in daily life and that is

usually called base 10. so if you look

2371 number here we can really split it

in the form that you see to the right

here if you try and take this expression

we have on the right here and evaluate

it you're going to get this number here

2 times 10 to the power of 3 this

evaluates to 2000 and this one here is

going to evaluate to 300 this one is

going to evaluate to 70 and the last one

is going to evaluate to one and if you

add these things up you're going to end

up with this number so this is how we

can take a number and uh make up a base

10 representation of it we can do the

same thing for 924 here or 47 here it

really is basic math you don't need to

have a lot of background in math to make

sense of this so we're going to use this

exact form and understand binary numbers

if you look at what we have here we have

a few binary numbers that are made up of

ones and zeros that's why it's called

binary because you can only have two

states or zero or one in your numbers so

we can really do the same thing we are

in base two so instead of using a ten

here we're going to be using a two but

it is the same operations we really did

if you take this and multiply and add

these things up what you're going to end

up is a base 10 representation of this

number if we go in the middle here we

have something we can easily do without

using a calculator the expression on the

left here is going to evaluate to

zero because we are multiplying with

zero the second one is going to be a two

because we are taking one and

multiplying this by two the others are

going to be zeros but the last one is

going to be 2 to the power of 4 which is

16 and we're going to add a 2 and this

is going to evaluate to 18. we can

actually bring up our calculator on

windows 10 i think it can help in this a

little bit we're going to bring it up

and we want to put it in a programmer

mode and we're going to go back on our

slide and find our number which is one

zero zero one zero so we're going to

type it out one zero zero one zero in

binary this is binary that we have typed

here so let's clear this and do one zero

zero one zero and you're going to see

that in the decimal it is 18 which is

what we came up by computing this in our

brain let's try the one we had before

that we couldn't really do in our brain

we're going to say one zero zero one

zero one let's do that we're going to

clear one zero zero one zero one this is

going to evaluate to 37 in decimal and

you can use calculators like this to

really do the transformations between

these different number representations

okay down below we have a one one one

which is going to evaluate to a seven in

base ten okay if we have three digits we

can really represent numbers between

zero and seven and you see a table here

that is going to prove that zero zero

zero is going to evaluate to zero in

decimal zero zero one is going to be a

one and if you go down to one one one

that is going to evaluate to a seven you

can try and use a calculator to prove

this and really understand how this

works if we use the three digits

representation our numbers are going to

look something like this in memory we're

going to take the bits in memory and

group them in groups of three and we are

going to use binary to actually make

sense of these numbers for example here

on the left this is going to be a one

the second one from the left is going to

be a six and this is going to be a six

as well this is going to be a zero this

is going to be a three because we have

one and two here we add those up we get

a three if this doesn't make sense you

can try and use a calculator you're

going to see that it makes sense okay so

what if we want to group our digits in

groups of four we can do that and we're

going to end up with something like this

the values we can represent are going to

go from 0 all the way to 15 and you can

try and prove this using the calculator

like we just did and it is going to look

like this in memory so what we really

are doing is grouping the bits in

different sizes of data and we have a

kind of formula that we can use to make

sense of the data in memory for example

on the left here we have zero one one

zero if we go back to our table and

defined zero one one zero this is a six

and we're going to know that these four

bits here are really storing s6 and

there are ways you can manipulate this

in your c plus plus program we're going

to see that you can also use five digits

and you're going to end up with

something like this and the numbers are

going to go from 0 all the way to 32 and

this is how it's going to look in memory

you can try and come up with what this

represents in decimal i'm not going to

tell you this but we can try and figure

out the one on the left here so it is 0

1 1 0 1. if we go back we're going to

come up to 0 1 1 0 1 which is a 13 here

so this memory location these five bits

represent a 17 number so if we want to

kind of generalize what we have talked

about in the last slides if you have one

digit you can really represent two

states zero and one if you have three

digits you can represent numbers between

zero and seven and you can go all the

way down and if we generalize this in a

mathematical formula we can say that if

we have n digits we're going to be able

to represent between 0 and 2 to the

power of n minus 1. and if you try to

plug in any number of digits you're

going to see that this formula works

okay so these are a few grouping of bits

we have in practice we can use eight

digits and we can represent numbers

between zero and two 255 if we have 16

bits we can represent this range if we

represent this range if we have 64 bets

we can really represent a really huge

range i can't even say this number it's

really bad okay now you should have a

pretty good idea of the binary system

and different representations we can use

to make sense of binary numbers in a

computer's memory the last thing i want

you to see is what we call hexadecimal

number system and it is a technique we

use to shorten the length of how we

represent a binary number in memory how

does it work well we take our number and

split it in groups of four bets and each

group is assigned a symbol we can use to

represent it if we have four zeros

hexadecimal if we have zero zero zero

one we're going to represent a one and

you can see that if we go up to nine

this is really similar to what we have

in the decimal number system but once we

hit 10 we're going to represent that

with an a in hexadecimal 11 is going to

be b 12 is going to be c 13 is going to

be d 14 is going to be e and 15 is going

to be f so how do we use this to

represent binary numbers let's see an

example here we have a huge number that

we represent in memory it starts with

zero and ends with the one here so the

first thing we're going to do is to

split this in groups of four and the one

on the left is going to be a one one one

one if we come back to our table here

one one one one means f so we're going

to represent this with an f if you go to

the second group of four bets we have

zero zero one one if we go back zero

zero one one means three so we're going

to have a three here i hope this makes

sense and we're going to keep using the

same transformations and we're going to

come up with one f 0 3 e 6 and we can

represent this binary number using these

symbols you can see that we go from

using 32 bits to using one two three

four five six seven eight symbols to

represent this and this is shorter and

easily manipulable by humans and we use

a zero x in front to mean that this is a

hexadecimal number i really hope this

makes sense so if we have numbers that

don't really fit in groups of four we're

going to go from the left and split this

in groups of four and we're going to end

up with a group on the left that doesn't

really meet our requirements and what we

can do is add the missing bits and make

them zeros and we call this operation

padding this is what you can do to

really represent any number in

hexadecimal if you don't have enough

bits on the left we also have another

system that is really not widely used

today but i am mentioning it here for

completeness it is called octal system

it goes from zero all the way to seven

and we can divide our binary number into

groups of three and represent using

these zeros and ones to shorten the

length of the binary number we can

really do the same thing we did with

hexadecimal so we're going to take our

binary number and divide this in groups

of three the one on the left is going to

evaluate to a 7 because it's 1 1 1 and

one one one evaluates to seven in octal

system the second one is also going to

be a one one one the third one is going

to be one zero zero if we go in our

table it's going to be one zero zero

it's going to be a four and you see we

have a 4 here and you can do the same

things until you have figured out the

entire number here and you see on the

left we are doing padding and adding a

missing bit and making it to 0 so we are

coming up with 0 0 1 and if we go back

to our table here 0 0 1 is a 1 and

that's what we put here so we're going

to put this number here it's going to be

15 61 41 70 47 7 and we're going to add

a zero in front to mean that this is a

number represented in the octal system i

really hope this makes sense okay so we

have seen all these binary numbers and

different number systems we can use to

represent them but how do we use them in

a c plus plus program well i'm glad you

asked here is a simple example of how

you can represent the number 15 through

different number systems in c plus plus

if you just say 15 like this it's going

to be in decimal if you add a zero in

front it's going to mean that the number

is in octal system so this can be

confusing sometimes if you do 0 17 it's

not going to be 17. so if you say 0 17 c

plus plus is going to interpret this

number as if it is in octal system and

it is going to turn this into 15. down

here you see the same representation in

hexadecimal we saw that you use a 0x in

front to represent that it is in

hexadecimal and this is going to be 15

representation in binary using zeros and

ones and you use zero b in front like

this i have to say that this was only

possible since c plus plus 14. so if you

are using an older standard of c plus

plus you want to be able to represent

binary like this and if we run this

program it is going to print the same

thing it is going to print 15 but we

stored the number using different number

systems let's go to visual studio code

and try this out okay here we are in a

folder i have on my system where i am

going to be storing my projects for this

chapter the first thing i am going to do

is copy code from a template project i

am going to go in and copy things over

and i am going to put these in 4 2

number systems i am going to open this

folder in visual studio code so i am

going to go to file close the folder we

have now and i am going to open up a new

one open folder and i am going to browse

to the location of my project i am going

to open this project here that says

number systems we are going to get rid

of the welcome screen and open our main

cpp file we're going to get rid of this

constival thing and clear everything we

have in the main function here the first

thing we want to do is to store an

integer that is 15 and we're going to

say and number one the exact same thing

we had in the slides and we're going to

store 15 in this variable here this is

going to be represented in decimal and

if we want to store the semi number in

octo we saw that in our slides we could

store this as 0 17. so let's do that

we're going to say it number 2 and we're

going to store in 0 17. this is not

going to be 17 this is going to be a

representation of a number in octo

system so we're going to say that this

is octo and we can represent the number

in hexadecimal as well so we're going to

say it number three and it is going to

0x because it is hexadecimal and we're

going to say zero f this is how we

represent it you can use lowercase or

uppercase it won't really matter let's

use uppercase here and we can use binary

because we are using c plus plus 20. so

we're going to say and number four and

we're going to store in a representation

of 15 in binary and it happens to be

four zeros and four ones and we have to

prefix this with a zero b this is how it

works so this is going to be in binary

and if we print all these numbers up

we're going to see let me not tell you

this what do you think we'll see okay so

i went ahead and typed this out what do

you think we will see when we build and

run this program before we do that we're

going to open a terminal so that we see

it here and we're going to go to

terminal run task we're going to build

with gcc let's wait and see if the world

is successful world finished

successfully we have a rooster program

click somewhere in this terminal and our

terminal is going to show up if we do

dur you're going to see that our rooster

program is here and if we run it i want

you to take a moment and guess what

we're going to see hmm number one 15

number 215 in number 315 and number four

15. this is really the same number we

are storing in these variables but we

are using a different representation

that is going to be convenient depending

on whatever it is we are doing if it is

more convenient to use binary we are

going to use binary if it is more

convenient use hexadecimal please do use

hexadecimal but the representation of

this number in memory is really going to

be the same i really want you to take

some time and let this sink in because

you're going to see these things a lot

of times in your career as a software

developer so please do yourself a favor

and make sure you really understand this

okay this is really all we set up to do

in this lecture trying to make sense of

the binary numbers we have in memory and

how we transform between them and

different forms of data that is easily

manipulable by humans all data is

represented by a bunch of grouped cells

of zeros and ones we have seen this as

the range of your data grows so will be

the number of digits you need to

represent the data in memory we have

seen that the hexadecimal system makes

it a little easier for humans to handle

streams of data in ones and zeros octo

has the same goal as hexadecimal but

it's almost no longer used in modern

times i just mentioned it here for

completeness we are going to stop here

in this lecture in the next one we're

going to look at integers in a little

more detail so go ahead and finish up

here and meet me there in this lecture

we're going to learn a little more about

integers in c plus plus integers are

represented by ant and z plus plus it's

what you see on the left here and they

are used to store whole numbers things

like 1 2 and 3. they typically occupy 4

bytes or more in memory but in most

times it's going to be 4 bytes so for

example if you have a variable called

age and it is an integer this is how

it's most probably going to look in

memory it's going to take four bytes and

i really want to make it clear what a

variable is it is a named piece of

memory that you use to store specific

types of data okay so here if we have a

variable named age it is a named piece

of memory edge is going to be the name

of that piece of memory and we can store

data in that memory it's going to look

like this in memory but the value is

going to be stored in here in binary

format i really hope this makes sense a

variable is a named piece of memory that

we can use to store different kinds of

data and okay now we're going to look at

a few examples of how you can work with

integers in your c plus program you can

define a few variables here we have one

that is going to store the number of

elephants we have you can declare it

like this and not put in a value and if

you do it like this the compiler is just

going to put in some garbage value that

is really not meaningful for your

program so you see the warning we have

here as a comment the variable may

contain random garbage value and this is

something you need to be aware of

another way we can define integers in

our c plus plus program is this

statement here that declares a variable

called lion count it's going to

initialize to zero if we use curly

braces like this it's going to

initialize to 0 by default we can also

explicitly put in a value we can do the

same with cat count and we can use these

variables to do operations for example

we can declare another variable and it

is going to store the number of

domesticated animals and we're going to

add up the numbers for dogs and cats and

we're going to store the result of that

in our variable that is called

domesticated animals this is something

you can do another thing that can be

problematic is trying to use variables

that you haven't defined or declared in

your program that is going to give you a

compiler error and the compiler is

basically going to say i don't know what

doesn't exist one here is i don't know

what this doesn't exist to is it is not

defined anywhere in the program another

thing you can do is try and store a

fractional number in a variable that you

declared as an integer and this is going

to give you a warning because fractional

numbers are usually bigger in size than

integers and this is going to lose some

of your data we don't really have enough

tools to understand this now but we are

going to understand this a little bit

later in the course but this is

something you can do you can take a

fractional number and store that in an

integer variable and we're going to do

an example and see how this behaves with

our compiler that is gcc10 okay here we

have mostly used curly braces to

initialize our variables but we can also

use parenthesis and this is going to be

as functional variable initialization

because we are using parenthesis and

this is mostly going to do the same

thing we saw in the last slide with

curly braces but when we come to the

example here where we are storing a

fractional number this is going to

silently chop off the data you have in a

fractional number and turn that into an

integer and this is called implicit

conversions but if we go to the last

example here where we are storing 2.9

into an integer this is going to take

this fractional number chop off the

decimal point and only store 2 in this

integer and this might not be what you

want and it is going to happen silently

so this is a really bad way to do this

if you want to do something like this it

is preferable to use curly braces

because you are either going to get a

warning that this is going to lose you

data or you're going to get a compiler

error and the compiler is going to

completely stop you from doing this and

again if any of this doesn't make any

sense we're going to go in visual studio

code play with us and see how the

compiler behaves with these things we

have another way we can initialize our

variables in surplus plus we can use

assignment and we have done this a

couple of times in the course but this

is something you can do and we are going

to play with this in visual studio code

in a minute and you're going to see how

it works okay by now we have seen three

ways we can initialize our integer

initialization which is basically using

curly braces we can use functional

notation which is using the parenthesis

and we can use the assignment

initialization which is what we have

here another thing i really want you to

to query for the size of your variable

here we are trying to print the size an

integer is going to take on our

operating system and compiler and if we

try to run this on our compiler it's

going to tell us exactly how much memory

an integer occupies in our program we

can either pass and explicitly like this

or we can pass a variable name and it is

going to work equally well okay ants are

mostly going to take up four bytes in

representation of three ants in memory

if we go from this zero to this zero

this is going to be exactly four bytes

and this is how it may look in memory

one other thing i haven't really talked

about on purpose is that there are a few

rules you have to follow to name your

variables in c plus plus one of those

rules is that a variable must start with

a letter like a b c d up to z or an

underscore you can't start a variable

for example with a number that's going

to be a problem after the first

character in your variable name you can

really put in anything you can put in

numbers you can put in letters you can

really put anything you want but the

first one can't be a number variable

names are also case sensitive so if you

have a variable called bike account with

and you have another one that starts

these are going to be two different

variables and uh you have to be aware of

this no spaces or spatial characters are

allowed in your variables you can use

underscores but you can't use something

like plus because that's going to be

confusing to your compiler and these are

a few rules you really need to be aware

of and you're mostly going to be fine

the general form for declaring and

initializing your variable is what you

see here you're going to pass the type

in this case we have used and because we

are learning about ants you're going to

pass the variable name and you're going

initializing your variable with of

course this is braced initialization

because it is using curly braces but you

can also use functional initialization

or assignment initialization and it is

going to work equally well okay now we

have enough information to go in visual

studio code and play with us okay here i

am in my folder for the projects of this

chapter i am going to hop over in my

template project and copy the files that

i need i am going to go up again

and go on the project that is called

i am going to go in and paste in my

files and i am going to open up this

folder in visual studio code i am going

to close the welcome screen here and

and i am going to do the usual take out

the things we don't need to save on time

i am going to put in a piece of code

that i have lying on my drive and we're

go through it to save on typing time i

don't want you to suffer watching me

type this the first thing we have is the

elephant count this is a variable that

is not initialized so this is going to

contain garbage data it's not going to

contain anything that is useful to us

but some compilers are going to usefully

put in a zero because that's a logical

number to put in here if you didn't

explicitly put a number in here the

second one is using curly braces and

this is going to automatically

initialize to zero the third one is

going to be explicitly initialized with

the 10 and the cat count is going to be

initialized with 15. you can try and

print this out and see what you come up

with after compiling this application

another thing we have seen is that we

can do something like this and put an

expression into our curly braces and the

value this evaluates to is going to

initialize this domesticated animals

variable and now you should know that

this is probably going to take 4 bytes

in memory because it is an integer

this is really how c plus plus works

most times so integers is mostly going

to be four bytes on your system and

we're going to query this a little later

in this video okay let's try and compile

this program and see if it actually

works we're going to start world and you

see that the world is successful another

thing we can do is try and use variables

we haven't really declared in our

program and you can guess what is going

and new number for example and putin

doesn't exist you know it's a number

that doesn't exist the compiler is not

going to know what this is because we

didn't declare a variable called doesn't

exist if you try to compile this you're

going to get a problem you see that we

have a problem before we even compile so

visual studio code is this smart it can

analyze our code before we compile it

and give us hints to problems that might

come up you see here it is saying

doesn't exist isn't defined so if we try

to compile this we're going to get an

error that we expect it's going to say

doesn't exist doesn't really exist i

don't know what that is so you shouldn't

really do that you shouldn't try to use

variables you haven't declared this is

we can also do functional initialization

okay another thing we can do is store a

fractional number in an empty variable

and we're going to see what this does

we're going to try and compile this code

you see we have a 2.9 we're trying to

store this in an integer if we try to

compile this let's try and use gcc let's

clear this let's bring up a terminal and

try to build this we're going to try and

run our gcc compiler on this program it

is going to say errol narrowing a

2.899 from double to integer c plus plus

20 isn't even going to allow this so

this is a good thing because you might

think that you have a 2.9 and some

compilers are going to chop this off and

store a 2 instead so this is one of the

safe things about this way of doing

thanks so i am going to comment this out

because otherwise our program wouldn't

compile now that we know how to use

these things we can try to print the

values in here okay i am going to put in

a piece of code i have lying around on

my drive i am going to remove these

spaces inside because it is annoying

let's do this and if we try and build

this program it should compile

successfully and if we run it we should

see our numbers we're going to go in our

terminal here and do der and we're going

to run rooster and we're going to see

elephant count is one because this is a

garbage value so it could really be

cat count should be 15 it is what we

have and a domesticated animal count is

25 because we have drug account

and we add that to cat count and we're

going to end up with 25. this is what we

expect now that we know how to work with

this we can also try and play with

functional initialization before i put

in my code i am going to comment all

this out because i don't want this to

disturb us as we work with our

functional initialization code so i am

going to comment all this out and go all

the way down and put in my code for

and you see here we have a variable

called ethel we initialize this to 5 we

have orange count which is 10 we have

and we have a bad initialization that is

not going to work it doesn't exist 3 and

doesn't exist 4 don't really exist so so

this is going to give us a compiler

and if we do something like we do in

narrowing the conversion function here

this is mostly going to compile and this

is going to chop off data and store a 2

instead of the 2.9 this is something you

should really be aware of and you see

the comment here says information lost

this is less safe than braced

initializer because breast initializer

give you a compiler error if you try to

do this and that's a good thing

so we also try and print these out so i

am going to tidy this up a little bit

and i am going to try and compile this

piece of code run task and world with

gcc the world is going to pass through

and if we do clear and run rooster we're

going to see apple count is 5 which is

what we have in here orange count is

going to be 10 so this is right fruit

count is going to be 15 because it is 5

and what is really worrying is that

narrowing conversion is 2 but we didn't

store in a 2 we started in a 2.9

and because an integer can really store

4 bytes 2.9 is more than 4 bytes and it

is going to store what it can and it is

going to chop off this 2.9 and only

store in a 2 so this is really something

you should be aware of sometimes this is

going to cause problems in your program

really really if you are trying to store

fractional numbers in an integer please

form because the compiler is going to

stop you from doing this if you try okay

so this is really the difference between

functional notation and breast

initializer notation functional notation

is not going to give you an arrow if you

try to store something that can't really

fit in a net it is going to silently

chop it off and put in whatever it can

and braced initializer is going to give

you a compiler error so this is the

difference between these two okay i am

going to comment this out as well and i

am going to put the starting comment

here and i am going to go down and show

you that you can do assignment

initialization as well i am going to put

in my code here because i don't want to

type it really and i am going to print

all this out and we have a bike account

variable that we initialize using the

assignment notation track count is going

to be seven fake account is going to be

bike account plus track count and we're

going to be narrowing conversion here

and we're going to see if this actually

works we're going to try and weld this

we're going to run the task to world

it is going to pass through you can

guess what we're going to see if we run

bike account is 2 track count is 7 which

is what we expect vehicle count is nine

and uh the narrowing conversion is also

chopping off what we have here so this

is something you need to be careful

about another thing i want you to see is

that you can check the size of your

variables in memory so we're going to

and i am going to put in a piece of code

to really play with this i don't want to

type all this because it's really

self-explanatory by now we're going to

print sites of ant and inside we're

going to say size of ant and this is

going to give us how much memory is

really occupied by an end and we can use

this form here by passing in a variable

name track count is a variable we have

declared and initialized here

so if we build this program

let's do that with gcc the build is

going to pass through and if we run

rooster we're going to see that the size

of int is four you're going to see that

this is in bytes and size of track count

is for as well because track account is

also an integer so these are all little

tools you can really use to

know how much memory is really being

used and occupied by your program and

this is really all we set up to do in

this lecture to learn as much as we can

about integers integers occupy 4 bytes

in memory for the most part and we have

seen different ways we can initialize

our integer variables we can use breast

initializers which is going to use curly

initialization using parentheses like

this we can also do assignment notation

using the from like this and we can use

size of to check the size of our integer

variables i have to say that these kinds

of initialization also work on other

variables but we took the chance to

introduce all these concepts using

integers this is really all we set out

to do in this lecture i hope you found

it interesting we are going to stop here

in this lecture the next one we're going

to start and learn about integer

modifiers go ahead and finish up here

in this lecture we're going to learn

about integer modifiers and these are

little things you can sprinkle around

your integer types to modify their

behavior a little bit but before we dive

let's talk about how we can store

positive or negative numbers in integers

and we can do something like this if we

put a tan inside our value 1 variable

it's going to work we can also put in a

negative number like minus 300

and it is going to work so what's the

this is signed by default and this is a

modifier we can apply to our variable

to signal that we have the possibility

to store in negative or positive numbers

and it is going to work if you only want

to store positive numbers in your end

variables you can use another

modifier called unsigned and if you put

in a negative number you're going to get

a compiler error we're going to see how

this works in a minute okay regardless

of whether your integer variables are

unsigned or signed they are going to

still occupy 4 bytes in memory so this

is how it's going to look in memory and

here is a simple formula we can use to

the range of values we can store in our

if they are unsigned or signed if the

number is inside you can use this

unsigned range formula and plug in the

in your data type if you are using a

this is what you're going to use and

here is a simple example for example if

we have an unsigned and this is the

range of values we can store we can

basically go from 0 all the way to 4

billion if the number is signed the

range is going to basically be divided

into half the half is going to go on the

left and store negative numbers and the

other half is going to go to the right

and store positive numbers and you can

see that we can basically go from minus

two billion to two billion if the number

is signed okay by now we have seen two

modifiers unsigned and designed but

there are others for example you can

flag your integer types as short or long

what does this do well this is a table

that i put together to try and come up

with all the combinations you can come

up with if you have a short variable it

is going to be two bytes in memory this

is the modification that this modifier

does to your type if you have short and

it's going to be two bytes if you have a

signed short and it's going to be two

bytes if you have unsigned shirt and

it's going to be two bites you can see

that the effect of short is really

shortening the original size in memory

for whatever type you applied this on

this is really working on an editor even

if we don't specify int here for example

short short here it's going to

we have two bytes because it's basically

an end that we have split into here in

the second column we have ant which is

going to be 4 bytes if it is assigned

and it's going to be 4 bytes this is

really the sizes you're going to come up

with if you use these combinations of

modifiers on your integer types one

thing i really want you to be careful

about is that these modifiers only work

for integral types so they work for data

types in which you can store

decimal or whole numbers you can't use

this on types in which you can store

fractional numbers like 2.9 that's going

to give you a compiler error now that

you have an idea about this why don't we

go in visual studio code and actually

play with us okay here we are in our

folder that contains our projects we're

going to do the usual and copy the files

from our template project and we're

going to put those files in our integer

modifiers project here let's open it up

and paste in the files we're going to go

up again and we're going to open this up

in visual studio code the first thing i

want to play with is storing positive

and negative numbers in our integer

types so we're going to say end value

one and we're going to store in a 10 for

example and we're going to do any value

and we're going to put in a minus 300. i

think this is what we had you know a

slide so we're going to keep this

if you try to print this out so we're

going to say value 1 and we're going to

and we're going to try and build this so

we're going to open our terminal so that

we can play with it right away

and we're going to run the task to world

with gcc the world is going to be

successful if we run our program we're

going to see that it's going to say

is -3 300 this is really cool we can

store positive numbers and negative

numbers in our end times and this is

4 bytes in memory we can prove this by

printing the size of value 1 and value

2. let's do that so we're going to say

size of value 1 is size of value 1. we

can also do it for value 2 size of value

2 and it's going to be size of value two

std and yeah if we build this again

we're going to run the test world with

gcc and uh we run our application it's

going to save four bytes so it doesn't

really matter if we store in a positive

number or a negative number it's going

to be 4 bytes this is the point i want

to make here another thing you can do is

very clear that you have signed numbers

in here and you can use the signed

integer modifier here so this is going

to give us the same result and if we try

run the task to build with gcc the world

is going to be successful if we run the

program we're going to get the same

result so if you don't put aside or if

you put it here it's going to be exactly

the same thing another thing you can do

is make it very clear that you want to

positive numbers in your variables we

can do that by using the unsigned

integer modifier so we're going to say

and value three for example and we're

this is going to be fine but if you do

unsigned and value 4 and put in a minus

this is going to give you a compiler

error because you save this is unsigned

and this really means that you want to

store in only positive numbers but you

are trying to put in a negative number

if you try to build this let's try this

we're going to run the task to build

with gcc we are going to get a compiler

arrow saying conversion from -5 to ant

this is not allowed you're going to get

a compiler arrow your program is not

going to compile so this is a compiler

error let's say this here and this is

really all i had to share about these

signed is going to mean that you can

store negative and positive numbers

unsigned is going to mean that you can

only put in positive numbers and if you

try to put in a negative number you're

going to get a compiler error now that

this is commented out if you try to run

the world is going to be good and we

will be able to run our program

and it's going to do whatever it was

doing before as we see here we also saw

that we could use the short and

long modifiers and we're going to put a

piece of code here that is going to

allow us to play with them so i don't

want to type this and if you don't want

to type this as well you can get this

code from the resource section it's

going to be left you can open the link

use the code copy the code and paste it

in here and really play with it because

the point is really not to type all this

the point is to understand what these

to your variables what we are going to

do we're going to try to print them out

and print the size they actually have in

memory we're going to do this in four

groups we're going to do one for short

and long we're going to do one for ant

here we're going to do one for long and

we're going to do one for long long

these are things you can do and we're

going to see how much memory is actually

being used by all these variables we are

going to start with the first group here

so we're going to go down and print the

size is out and this may be really hard

to wrap your brain around but they are

see out statements that we have been

doing all along i am going to split this

on different lines so that you can

we have an output statement for a short

var which is what we have here so we

expect this to take two bytes and all

these things are probably going to take

two bytes let's try and build the

program with gcc the bullet is going to

be successful we are going to run

rooster and you're going to see that

short end is two bytes signed short is

two bytes and everything is basically

in this group here and we did guess

right the next thing we want to try out

we are going to go down and give

ourselves some breathing room

and we're going to paste this in and

we're going to separate these again so

that we can see what is really happening

here and i think this is really enough

so we're going to see the sizes for the

thanks we have in this group here and we

expect this to take four bytes so let's

try and run the world task to build with

gcc the world is going to be good we can

run the program like we usually do and

you're going to see that ant variable is

4 bytes and everything in that group is

4 bytes and this tells you that

regardless of the side and unside

modifiers you put here it's going to

really use the size of it here okay it's

going to take four bytes in memory let's

try this group here we are going to go

down and put in the code to print the

and this is what we should use

let's split this on different lines so

that it is easier on the eyes and again

if you don't really want to type this

you can get the code from the length

resource section you're going to find

the code here and you can copy and paste

and really play with us but it is

helpful to really type these things out

and really bring these things in muscle

memory because it's going to help okay

so we have this and we're going to try

and run the world task with gcc the

build is good we're going to go in here

and it is going to say long variable is

four bytes and everything in this group

is basically going to be four bytes

in here the last one is this long long

it is going to really give you a huge

for your values you can store in the

variable but don't really trust my world

let's try this out so that you can see

for yourself we are going to go down and

really put this in so we're going to

give ourselves some breathing room

and what we are really doing is printing

the sizes for the variables that we have

the world is going to be good

and we're going to see that long long is

eight bytes eight bytes gives us a

really huge range of values okay this is

really all we set out to do in this

lecture to learn about these integer

modifiers they modify the way your

integer variables behave for example we

can specify that we only want positive

numbers all that we want to both store

positive and negative numbers for that

you're going to use designed or unsigned

modifiers you can also shorten or

lengthen the range of values you can

store in your variable by using the

modifiers short and long and from the

output of a program here you can really

see all these effects here this is

really all we set out to do in this

lecture i hope you found it interesting

we are going to stop here in this

lecture in the next one we're going to

start and learn about fractional numbers

go ahead and finish up here and meet me

there in this lecture we're going to

learn about fractional numbers and as we

work with these numbers i want you to

keep in mind that any piece of data you

work with in your c plus program

is ultimately going to be stored in the

form of ones and zeros in memory

functional number are also called

floating types in technical terms they

are used to represent numbers with

fractional parts in c plus plus and many

other languages and we have three types

that we can use in c plus plus we have

double and long double and the main

difference is in the size they occupy in

memory a float takes four bytes a double

takes eight bytes and the long double

takes 12 bytes typically so as the size

goes up you can also notice that the

precision goes up so what is the

precision the precision is basically the

number of bits you can represent with

that type starting from the number in

front of the decimal point so if we look

at this number here we can try and

figure out its precision so we're going

to count 1 2 3 4 5 6 7 8 9 10 11 12. the

we're really not able to represent a

number like this with a float

the smallest thing we can use to

is a double because the precision is 15

and it is more than what we need for

this number which is 12. one thing you

should remember is that the number in

front of the decimal point is also

counted then when you are trying to

figure out the precision for your

floating point numbers in c plus plus so

here we have an example of how we can

declare and initialize floating point

numbers in our c plus plus program

number one is a really huge number so

you can guess that this is more than we

can handle with the float we're going to

see how this is handled by our compiler

a double has a precision of 15 so we

should expect to store more numbers than

we did in a float a long double should

be able to handle this without a problem

because if we go back to our table here

our long double here should be able to

handle this better than double but it is

possible that it is the same thing as

double depending on the compiler

implementation and if we try to print

out the sizes here we're going to see

what the compiler gives us we're going

to do this when we try this in visual

studio code okay and here we are trying

to print out the precision of these

numbers we can use a special setting on

our stream to control the maximum

precision that we can see here you see

that we are trying to show the precision

for each number there is a special

setting we can put on stdc out to make

it control the precision to a given

number here we are using 20 and we're

going to see that for number one this is

going to be seven digits for number two

it should be 15 digits or something

close to that the specifics are really

dependent on the compiler implementation

and for long double it should at least

be the same as double or even more in

some cases okay here we want to see that

we can also have narrowing errors

if we try to store something back in a

float and a float can't really handle it

here we have a number with a lot of

digits one two three four five six seven

eight nine and we know that the float

can only handle seven digits so

this is probably going to give us a

compiler error as we've seen for breast

initialization if we use functional

initialization this problem is not going

to be code at compile time so we're

going to end up with a chunked piece of

data and we're going to see this when we

play with this with visual studio code

and another format we can use with

floating points is that we can use

scientific notation and it is basically

a way we can use a power of 10

multiplier to multiply with our floating

point number so for example here number

5 is going to be this number 1 9 2 4 0 0

0 23 we can use a floating point

scientific notation to represent this

so what we're going to do we're going to

say 1.9 and we're going to multiply this

with 10 to the power of 8. this is what

this means this 8 here means to multiply

with 10 to the power of 8. and if we

multiply with that that basically means

moving the decimal point 8 digits to the

right so we can go one two three four

five six seven eight and it is going to

end at these three here and it is going

to be basically the same number number

seven is also another one and if we do

this we're going to pad with zeros after

these four and we're going to end up at

this same location as the three but it

is going to be a zero we're going to see

about that in a minute and number eight

is another floating point number and we

can use scientific notation to represent

it just like you see with number nine

we're basically going to have the same

thing when we have a minus in here it

means we're going to multiply with 10 to

the power of minus 11 and this is going

to give us a number below one thing zero

point zero zero seven or something like

that so we're going to go 11 digits

after the zero here and if we count one

two three four 5 6 7 8 9 10 11 and the

decimal point is going to go after three

and we're going to basically end up with

the same thing here we're going to play

with this in a minute and you're going

to see that all this makes sense and

don't forget that any piece of data we

store in a computer is going to be

ultimately represented by ones and zeros

in memory and for floating points we

don't use the number systems like we've

done for integers there is a special

system that is used to do that but it is

a little bit complicated to cover in a

course like this i am just going to

point you to it if you are interested

and when you are done with this course

you can come up and read on this the

main point is that any piece of data

that you represent in your c plus plus

program is going to be represented in

terms of ones and zeros in the memory of

your computer okay there are a few

things you can do with floating points

that you can't really do with integers

for example you can divide with zero if

you take a floating point number and

divide that with zero you're going to

get what we call infinity if the number

is positive you're going to get positive

infinity if the number is negative

you're going to get negative infinity

and you can take two floating point

numbers that are zeros and divide them

and what you're going to get really is

not a number it's something called nan

which stands for naughty number

and uh your program is going to not

crash but very few things you can't do

with these things for example you can't

add them up you shouldn't really do this

it's probably going to end up bad for

your program here we have a few examples

we have three numbers declared they are

doubles they must be occupying eight

bytes in memory number 10 is initialized

to 5.6 11 is initialized to zero because

we are using the braced initialization

and infinity here is the result of

dividing a number by zero so it's going

to be positive infinity because number

10 is a positive number if you go down

we're going to print number 10 divided

by number 11 and we're going to say

yields we're going to put the result out

we're going to see that down here on the

second line you see that we are trying

to add something to infinity and this is

also going to yield infinity because

think of infinity as something super big

and if you add something small to

something big it's still going to be

something big down here you see that

result equals number 11 divided by

number 12 and these two are zeros so

we're going to end up with none and

that's what we're going to print in this

down to the bottom okay you should

really remember to put in the suffixes

when you are initializing your floating

point numbers otherwise the default is

going to be double this is what we mean

by this you see this floating number we

have a suffix that is f to mean that it

is a floating number if you don't put

that in this is going to be interpreted

as double and the compiler is going to

try and turn that into a float by

chopping off things that can't really

fit in a float so to really make it

clear that you are stirring in and

loading number please put this f suffix

here for double you don't need to put

anything because it is the default

assumed by the compiler but for a long

double you have to suffix this with l

just like this so that's what we really

mean here we have seen that the

precision for float isn't really enough

for many of the computations we might

want to do in our c plus plus

applications okay we have talked a lot

about floating point numbers let's head

to visual studio code and actually play

with them okay here we are in our folder

that is going to contain our project the

project is going to be called fractional

numbers so we're going to copy our files

and put those in and i'm going to go up

again and open this in visual studio

code we're going to close whatever it is

we have opened now we're going to close

folder and we're going to open our

project in visual studio code and we're

going to do the usual and remove things

we don't need in here the first thing we

want to do is to store a few floats in

our program we're going to declare and

initialize a few floating point numbers

we have number one number two and number

three and we want to make it clear that

the sizes are what we expect we are

going to open a terminal window here and

we're going to build with gcc run the

task to weld with gcc the world is going

to be successful we're going to come to

our terminal click a little bit and

we're going to type dir we're going to

see that a program is in place if we run

it we are going to see that size of

float is 4 size of double is eight and

size of long double is 16. this is what

we expected another thing we can do is

try and play with the precision of these

numbers and see what we can really go

away with okay so we're going to

actually put in a piece of code to play

with this we're going to add a setting

to our sddc out stream so that we can

control the precision but for this to

work we need to bring in a library that

is called i o manip so we're going to

include that i o manip and how do i know

this i usually consult the c plus plus

standard library documentation and you

are not at the point where you can

really understand it right now so we're

going to be putting in these things here

and explaining them as we go and i made

the type here it is io manip and you see

now this is recognized our program

should compile so we're going to try and

weld it so that we can try this out

we're going to build with gcc the world

is going to go through we can run our

program we're going to do dur and clear

and rooster to run you see that things

start to go off at sex and if we count

what we have here it is one two three

four five six seven we can only

represent seven numbers accurately with

a float and after that we're just going

to have garbage because the computer

can't really make sense of whatever we

seven digits that we can legally

represent with the flood so the

precision for our floating point number

here is seven i really hope this makes

sense let's check out number two

we are using double so precision should

be around something like 15. so we are

putting in a number one through nine and

we are starting over zero one two three

four five up to zero again if we look at

what we have in the output here we have

one two three four five six seven eight

four five six and here things start

falling off after our sixth year and if

we count we're going to have 1 2 3 4 5 6

7 8 9 10 11 12 13 14 15 16 17 digits

this is the precision we are having this

compiler for double 17 so it is

something around 15 and we should expect

to have something more than that or at

least the same thing as double with long

double so if we look at this you see

that it is one two three four five six

seven eight nine zero one two three four

five six seven eight nine we are able to

represent up to 20 and you can see that

long double leaves up to even the

precision of 20 that we have set with

std set precision here okay i really

hope now that you have an idea about

these precisions we have with our

floating point types in c plus plus

programs another thing i want you to see

what kind of narrowing errors we can get

if we try to initialize with something

that can't really be represented by a

floating point number and here we have a

float it is called number four and we

are trying to put in something that is

bigger than we can really fit in it has

more than seven digits so one two three

four five six seven eight nine it is

more than seven digits and we would

expect to have a problem with this

initialization let's try and build this

with gcc we're going to do that and this

is going to work successfully so this is

going to silently chop off our number if

we try to print it out we're going to

say sddc out number four and we're going

to world again run the test tube world

so that our changes are taken into

effect i'm going to do dur and do

rooster and this is going to print our

number you're going to see that after

we have junk our number has been

basically chopped off and this is junk

because we can't really represent this

with the double the 16 here has been

chopped off because we can't basically

represent this with the floating point

number if we change this to double this

is going to probably give us what we

expect so let's run again world with gcc

the world is going to be good if we run

the program it is going to show us the

same thing okay this is a really good

learning change why are we having the

before even if we changed the type to

double try to think about it the reason

is the suffix here is still saying f and

this is going to be stored as float in

memory so if we want this to really be

treated like a double we can take out

and if we build again and run the

application now you're going to see that

we see the 23 this is basically being

correctly stored as a double this is a

really good thing you should keep in

mind if you don't put in your suffixes

here the number is going to be

by now i hope you see that if you really

try to put more than your floating point

the number is going to be chopped off

and only the precision that it can

handle is going to be stored in i hope

this makes sense and you see that the

behavior for numbers is really different

we got the compiler error when we try to

do narrowing conversion with integers

but now it is silently chopping off our

number if we try and use functional

notation i think we're going to get the

same result and change this back to a

float and uh use float here and if we

both again let's go to terminal run task

use gcc we're going to run this

let's run rooster and you see that we

get the same results our 23 is chopped

off here we can also use the assignment

notation here just like we did with

integers and this is going to do exactly

the same thing it is going to chop off

the 23 here and we're going to have some

garbage which is 16 in this case if we

weld the gun the world is going to go

through and if we run we're going to see

as it's in here okay narrowing

conversions are something you should be

aware of when storing your floating

point numbers and you should really

remember to put in your suffixes here

and other thing we have seen that we

should really play with is scientific

as the comment here says what we have

seen so far in floating point numbers is

fixed notation it is what we have here

but we can also use scientific notation

which is exactly what we described in

the slides and what we have here for

example is e8 and it means that we are

going to multiply this number here

with 10 to the power of 8. if you go

down here we have number 9 so we have

and we have e minus 11 and what this is

going to do is multiply with 10 to the

power of minus 11. this is how i can

represent this here and we can print

these numbers out to really play with

them to make a difference with what we

have been doing before we're going to do

sddc out and put a dividing line here

this is one way we can do this so we're

we're going to weld this so we're going

to run the attached world with gcc 10

the world is going to go through if we

do rooster we're going to see that our

number here number five is what we

expect number six is the same thing but

we used scientific notation to do this

because we took this number and

multiplied by 10 to the power of eight

number seven should be almost the same

thing but the lower 23 here is going to

be chopped off because we haven't

specified it we're just multiplying with

10 to the power of 8 so that's why we

have 0 0 here i hope that makes sense

and if you look at number 8 you see that

we stored it like this without using

scientific notation we used fixed

notation but on the terminal it's going

to be printed out in scientific notation

and this may be pretty cool the main

usage for scientific notation is to make

sense of numbers that are really huge so

the way you interpret this you're going

move these numbers after the decimal

points with 0 in front and it's

basically going to be like this so if

you count the zeros you have here we're

3 4 5 6 7 8 9 10 and 11 is going to be

directly after three and you're going to

get the number here this is what we mean

and number nine was explicitly stored in

using scientific notation and you see

that we have the same thing you can play

with these things and really make sense

of them and again we didn't specify any

suffix here so these are going to be

interpreted as doubles but this is not a

problem because they are doubles here

okay we are making some progress with

this lecture which is a little lengthy

the last thing we want to do is to play

we're going to put a message here to say

what we want to do and we're going to

have number 10 which is going to be

positive we're going to have number 11

which is going to be zero number 12 is

if we take 10 and divide that with 11

we're going to get infinity because we

are dividing a floating number with zero

if we try to print that out we're going

and we're going to get infinity for this

result here because we are trying to add

something small to infinity which is

something really big and if we all

trying to divide zero with zero in

we're going to get what is called

naughty number and if we print that out

we're going to see this in a minute

let's build this with gcc we're going to

weld successfully let's clear this out

so that we don't have noise in here and

we're going to run rooster and you see

here it says infinity and none which is

and if we go down here it is saying

number 10 divided by number 11 and

number 11 is zero you see that here it's

going to yield infinity if we add five

to infinity we're going to get infinity

and if we try to divide a zero by a zero

we're going to get none which is really

a way to tell you that you're doing

something wrong you should really be

one other thing i want you to see is

that if you turn this five into a minus

five and build again we're going to

build with gcc and we're going to run

we're going to get minus infinity so if

you divide a positive number with zero

you're going to get positive infinity

and if you divide a negative number with

infinity you're going to get negative

infinity and this is what we see here

this is really all we set out to do in

this lecture i hope you found it

interesting and again the big message is

that any data type you're going to be

handling in your c plus plus program is

going to ultimately be stored as ones

and zeros in memory and we have learned

about floating point numbers float

double and long and they have these

properties you see here and you should

use them with this in mind otherwise

you're going to have problems with your

precision make sure you are using the

correct precision that you need in your

program we are going to stop here in

this lecture the next one we're going to

try and learn about booleans go ahead

and finish up here and meet me there in

this lecture we're going to learn about

booleans booleans are types that can

store two states in c plus plots it can

store either true or false and we can

use this to really do decisions in our

program if you look in the program we

have here we have two variables declared

and one is called red light the other is

and we have true and false inside one

thing we can do in c plus plus is make

decisions we can say if the red light is

print a message that says stop and if

it's not red we can print a message that

says go through we can do that and

booleans are really used in this way to

make decisions in your c plus plus

program we haven't really learned about

if statements in this course but i am

throwing this in here to really drive

the point home that we can use this to

make decisions in our program down here

we have another way we can do this we

can actually use the variable itself

without checking if it is equal to true

or false and we are going to get the

same message the point here is that if

green light is true we're going to say

the light is green if it's not we're

going to say the light is not green you

can do something like this and again the

big point here is that booleans data

types are used to store two states true

or false in your c plus plus program

okay by default if you print a boolean

that has two in it you're going to get

true and this is what you see here and

if you print one that has zero in it

you're going to get false we can change

that with a special setting that we can

apply to our std out stream and you do

that like this with std bull alpha and

we're going to play with this in a

if we try to print with this setting

applied we're going to see true on false

and not c 0 and 1 like we did before

we're going to play with this in a

minute and you're going to see another

thing you should know is that booleans

8 bits in memory they take up an entire

bite so you may think that this is

wasteful and it is but with the amount

of memory that we have today this is

really not a big problem but if you are

working on a device where memory is

really a problem there are techniques

you can use to pack even more data in a

byte and we're going to learn about that

later in the course okay so this is

really all i have to say about booleans

we're going to go to visual studio code

and play with them in code okay here i

am in the folder for my project here i

am going to do the usual and copy the

and i am going to go in my project on

booleans i am going to go up and open

this up in visual studio code i am going

to close the current folder open the new

one and browse to my project this is

going to open up in visual studio code

and i am going to close the welcome

screen here i don't need it anymore

so i'm going to remove what i don't need

and we are going to play with the exact

code that we had in the slides we're

going to declare two variables one is

going to be red light the other is going

to be green light they are going to be

booleans and in red light we're going to

store a true and story false in green

light and we can make a decision like

this so try to guess what we're going to

plant in this program we're going to try

and decide and say if the red light is

true we're going to print stop

if it's not true we're going to fall in

go through if we look at our program in

red light we have a true so this should

really win and we should get in this

block here i hope this makes sense so

let's try and build this program to see

that it actually works so we're going to

build with the gcc we're going to run

our program and our terminal just went

away we're going to create a new one no

and uh if we do dir we're going to see

we run it it's going to say stop okay so

in red light we have true the test is

going to succeed here and we're going to

fall in this block and say stop i hope

this makes sense you can try to store a

and both again going to world with gcc

if we run this program now it's going to

say go through because red light is not

true anymore this is really what we mean

when we say that we can make decisions

based on booleans in our c plus plus

code we can also try another example

we're going to say if green light is

we're going to say the light is green if

it's not we're going to say the light is

not green and this is another form we

can use instead of typing the entire

comparing red light to true here and

again we're going to learn about all

it is just because i thought that

talking about bulls without showing

tests like this is really not going to

drive the point home for you so try to

understand this as simple tests you can

do in math if one value is true i am

going to do something if it's not true

i'm going to do something else this is

what we are doing here okay this program

here is going to check if the green

light is true so we're going to look

here green light is not true so we

should fall here and print this message

that the light is not green

let's build the program the world is

going to go through we're going to run

and you're going to see go through and

the light is not green this is what we

have here another thing we can actually

try to see is the amount of memory that

a boolean takes up so we can use sizeof

to do that we have seen this before if

we build with gcc we're going to go

and we can run our program to actually

this message and you're going to see

that bull is actually going to take up

one byte in memory this is what we saw

in the slides another thing that can be

really confusing is printing out boolean

values for example here we are trying to

print great light and green light let's

go up and actually change them a little

bit for example take green light here

and we're going to go down again and

here we are trying to print them out red

light is going to print whatever value

we have stored then and green light is

going to store whatever value we have

stored in and again true is going to be

and false is going to be printed out as

a zero let's try and build this we're

going to build with our gcc compiler the

world is going to be good we're going to

run this and you're going to see that

red light is zero because we have a full

and green light is going to be one

because we haven't a true here if you

try to print out boolean variables

you're going to get one and zero by

default if you really want to see true

and false there is a special setting you

can apply to htdc out and you do that by

alpha and you do it like this

and if you try to print again we are

going to get true and false right now

okay let's try and print again and we're

going to work this with gcc and we're

and now you see that we see red light is

this is really all i had to share about

booleans in this lecture i really hope

it drives the point home that booleans

are mostly used in making decisions in

your program and that's what you're

going to be mostly using them for and

another thing is that they take up one

bite in your memory we are going to stop

here in this lecture the next one we're

going to try and learn about characters

go ahead and finish up here and meet me

there in this lecture we're going to

learn about characters and text and we

use a data type called car in c plus

plus to represent characters and this is

basically how you use it you store in

characters like abc and here you see

o w and you put your characters in

single quotes like this to mean that

they are characters if you don't do that

you're going to get a compiler error

after you have your characters declared

and defined like this you can print them

out with stdc out and we're going to see

them on the terminal car occupies one

byte in memory so it's going to take up

eight bits okay so one thing we can do

is map each value in these 256 possible

values to a character and we can do

something like this for example we can

33 represents the exclamation mark

48 represents the character 0 49

represents the character 1 50 represents

the character 2 and we can keep going up

and say for example 70 represents f 71

112 represents p you can really use a

mapping like this and come up with

representations of your characters in

memory and this is what we do you can

learn about this encoding and on the

link here this is a real thing and it is

called the ascii encoding that takes

characters and stores them in one byte

and the data type to store these

characters in c plus plus is car if this

doesn't make sense please bear with me

we're going to play with this in visual

studio code and it is most probably

going to make sense okay it is possible

to assign a valid ascii code to

a car variable and the corresponding

character will be stored in that piece

of memory so once you have that you can

choose to interpret that either as a

character or as a number that is

something like an integer this is what

we really mean if we declare a variable

called value which is of car type 65 is

going to be stored in memory but the c

plus plus program is going to interpret

this as a character if we go back to our

table and see what is represented by 65

this is what we're going to find we're

going to find that 65 represents a

and if we print this out by default it's

going to print a it's not going to print

65 but there is a way you can take this

character value and turn that into an

integer and print it out and you see

that here we are saying value and and we

and and in the parents we have a value

this is basically a way to say we wanted

to take the value and interpret that as

an integer and we're going to learn a

little more about static cast later in

the course but it is basically a way to

transform between data types and in this

case we are trying to transform from car

to end and we're going to print this out

okay what we just described is the ascii

encoding a technique by which we can map

a byte two characters and use that to

represent characters this technique

doesn't work well if you have languages

like arabic japanese and chinese because

they are completely different beasts

there are better ways to represent

characters in your c plus program and

that's usually unicode but that's really

out of scope for a course like this so

i'm not going to describe that anymore

okay this is really all we need to learn

about characters we're going to head to

visual studio code and play with them

okay here i am in my working folder i am

going to go in my template project i am

going to copy things over i am going to

put that in my characters and text

project and i am going to go up and open

this up in visual studio code we're

going to close the welcome screen here

we're going to open up main cpp and

we're going to put in the code to play

the first thing we can do is declare

characters like this we can put in a r

r o w here and we're going to see this

printed out if we run this program we

are going to put in some code to play

we have a few variables declared that

we go from character 1 through character

5 and these are the characters we are

storing and this is and this is the

format you're really going to use to

declare your characters after we have

them declared we can print them out like

we print any other variable and we can

try and compile this program and see

what we're going to get but before we do

that i would invite you to try and guess

and we're going to build with our gcc

task we're going to world the build is

going to go through and if we run

rooster we're going to see that we are

a r o w we are storing our characters

and and we are able to print them out

this is really how you work with these

guys another thing i want you to see is

the size that a character occupies

in memory by that i mean card type it's

going to occupy one byte in memory and

that means that we can only have

256 different values that go between 0

and 255 if we have decided to store in

positive numbers we are using the

knowledge we learned from the integers

lecture if these calculations we are

doing here don't make sense please go

back and check that out so down here we

are declaring a character type the name

is value and we are putting in a 65. the

thing is if you try to print this value

here it's not going to print 65 it's

going to print a which is a character

representation of 65. if you remember

from our ascii table we had these

mappings between characters and integers

and 65 mapped to the character a

upper case so if we print this out this

is going to give us a but we have the

interpret this as a number and we can

pass this through a static cast and it

is going to take a value turn this into

an integer and we're going to be

printing this integer on the console and

we're going to see it we're going to try

this out so we're going to run the task

to build with gcc the build is going to

go through we're going to run rooster

and you're going to see that value is a

and the value and is 65 because we

decided to interpret whatever is in this

value as an integer and not as a

character as it is done by default this

is really all we set out to do in this

lecture i hope you found it interesting

we are going to stop here in this

lecture in the next one we're going to

try and learn about the auto key world

go ahead and finish up here and meet me

there in this lecture we're going to

learn about the auto keyword in c plus

this is a keyword that is going to let

the compiler deduce the type for you and

this is going to come in handy when you

have longer type names that are really

hard to type we can't really give you an

example of that because that requires to

have a good number of concepts mastered

in clause plus but we are measuring this

here for completeness because we are

talking about variables and data types

so let's hear how we can use this here

we have an example where we are saying

autovar one and what we initialize this

with is an integer so the compiler is

really going to try and guess the type

of this thing and that's the type it's

going to assign to variable one this is

what ocho is really used for if we pass

inside and it is a double because we

so it is going to deduce a double if we

pass a suffix of f it is going to

interpret this as a fluid if we pass l

it is going to interpret this as long

double and if we pass in a character

it's going to interpret this as a

character and this is really the essence

of what auto is used for it is used when

you don't really want to explicitly type

the type of your variable and you want

the compiler to fill in that for you or

it gets it for you down here you see

that we have a few examples with

integers so we can make this unsigned

lung through this suffixes and the

compiler is going to deduce the type

based on what we pass in our initializer

here down here you see that we have a

few examples with integers if we pass a

suffix of u this means that we are

storing an an unsigned integer so that's

what the compiler is going to deduce if

we pass ul it is going to be unsigned

long if we pass in ll this is going to

be long long and that's what the

compiler is going to deduce here you see

that we are trying to print the sizes of

these variables and we trying to

that the compiler deduced the right type

and we are going to go to visual studio

code and actually try this out

okay here i am in my working folder i am

going to open my template project i'm

save my files in the auto project here

so i am going to go in and put in my

files i'm going to go up again and i am

going to close whatever it is i have in

visual studio code because we're going

to create a new project i am going to

open my new folder we're going to close

the welcome screen here and we're going

to remove whatever it is we don't need

and we are going to put in the code we

basically had in the slides i am pasting

this code in to save on some time

because i don't want you to see me type

these things we're going to save some

so the first statement here declares a

variable var1 the type we don't really

know but we're going to let the compiler

and we can try and actually hover over

this and we're going to see that the

compiler already deduced that this is an

integer if we go to vira 2 this is a

double if we go to var3 you see it's a

float if you go to var4 it's long double

if you go to wire 5 it's a character you

can see that visual studio code can even

see what the compiler is going to deduce

before we even compile the code this is

the beauty of visual studio code we're

going to look at virus 6 you're going to

see that it's going to be unsigned and

if we go to var 7 it's going to be

unsigned long if we go to var 8 it's

going to be long long this is really

cool and you can see that our types are

correctly deduced visuals video code was

really helpful in showing us these types

but we want to be sure by running this

piece of code and seeing whatever size

the deduced type is for example for var1

we guessed that it's going to deduce an

in size we're going to try and run this

we're going to open our terminal here

and we're going to go to terminal and

run task we're going to build with gcc

and by the way if you want you can build

with the compiler from microsoft by

coming to terminal here and choose it

with world with msvc but gcc is my

favorite compiler and i am going to use

it if i can so we're going to hit enter

and enter we're going to see that our

rooster.exe file is in place if we run

it we're going to see our sizes so var

one occupies four bytes in memory

var2 occupies for eight bytes in memory

double fire 3 occupies 3 bytes because

it is a float var4 occupies 16 bytes

because it is a long double

and var 5 better occupy 1 byte because

it is a character and we see the same

vera 6 virus 7 and var 8 and this proves

that the auto keyword is really doing

its job it is deducing the types for our

variables without us explicitly

specifying the variable type we didn't

have to do something like and or double

or whatever we can let the compiler do

that for us and this will come in handy

many times this is really all we set out

to do in this lecture and i hope you

found it interesting in the next one

we're going to look at how we can do

assignments and assign data to our

variables in a unified way go ahead and

finish up here and we'd be there in this

lecture we're going to learn about

assignments and the basic idea i really

want to drive home here is that after a

variable is initialized like we've been

doing all along you can later assign a

new value to it for example here we have

our one declared it is an integer we can

print it out and it is going to print

one two three but later in the program

we can put in another value for example

here we are putting in a 55 and if we

print var1 it's going to be 55 this time

the same idea can be extended to doubles

you see here we are doing the same thing

booleans we are doing the same thing

here the state is declared force and we

are printing that and after we are

changing this to a true value and if we

print that it's going to be true one

thing you really need to be careful

about is if you are doing auto type

deduction the type is not very apparent

by looking at the declaration of the

variable here for example here by

looking at o2 var 3 we don't really know

what that is and it is very easy to try

and put in a value that is illegal for

example here we have deduced an unsigned

integer which is only going to store

positive numbers but we are putting in a

minus 22 and this is going to be a

disaster we're going to get a compiler

error and this is going to be bad so be

careful when you are doing a type

deduction in your assignments that you

do to your variables this is really all

we have to share in this lecture let's

hop over to visual studio and show you

this in action okay here i am in my

working folder the project we're going

to be working on is four nine here

assignments i am going to grab my

template files and put that in this

folder here and i am going to open this

up in visual studio code so let's close

and open the folder and we're going to

close the welcome screen here we don't

want it and remove whatever we don't

want from this file here the first thing

we want to do is put in the code for our

integer variable var1 and show you that

assign a new value to it after it was

initialized and if we run this code

we're going to see var1 to b123 and the

second statement is going to say var1

55. that's what we're going to see let's

bring up our terminal and we are going

to run the task to build with gcc

and if we hop over here in the terminal

we're going to see that our rooster.exe

file is in here if we run it we're going

to see var one one two three var 155

exactly what we expect we have stored in

a one two three at initialization using

braced initialization here but after

later on in our program we have decided

to put a different value in this

essentially reusing it to store

something else this is the basic idea

here we can do the same things with

doubles but before we do that let's put

in a separation line so that we can see

these vents clearly in the terminal and

we're going to go down and put in our

so we have a double variable called var2

in and then we're going to assign a new

value to it and that's going to be 99.99

if we print that out we're going to see

let's work and see this in action we're

run the program now it's going to save

r1 is one two three four one fifty five

but we're also going to see that viral

99.99 it's going to show up here okay

let's put in another separation line

because we're going to need that in a

we can do the same things with booleans

here we are using this as just an

essentially extends to any other kind of

variable you're going to have in your c

plus plus code if you initialize it with

some value you have the option to change

that value later on in your program by

assigning that value to that variable

essentially what we are doing here the

variable state which is a bull

was initialized to false we're going to

print that out and notice that we have

this setting to allow us to see true or

false instead of ones and zeros we have

seen this in a few lectures back

and later on we are assigning true to

this state and we are printing that so

if we print these things out we're going

to see false and true for the state here

and the world is good if we run the

we're going to see false and true and it

is exactly what we expect again you

really need to be careful when you are

using auto type deduction because you

might have some serious problems if you

are not paying attention let's put in

the code so that we can play with it

here we have a variable called var 3 and

the type of it is not specified

explicitly we are letting the compiler

deduce this and because our initializer

here is an unsigned integer the compiler

is going to deduce that it is an

unsigned integer the problem will come

if you try to store in a negative number

the compiler is not going to give you a

compiler arrow it is going to silently

that we don't really want in there we

want a minus 22 and you can see that

this is what the compiler is turning our

value into we want a minus 22 in this

for three but if you hover over this

minus sign here in visual studio code

you're going to see that the value that

we have in is not what we put in we put

in a minus 22 and we are getting a

really large number close to 4 billion

so this is really something that can go

silently wrong in your code and you're

a hard time trying to figure out why

your code is not doing whatever it is

you want so be careful about this let's

try and weld this so we're going to

the world is going to be good you're

going to see that we're not even going

to get a compiler arrow if we run this

and we're going to see that viral 3 is

exactly what visual studio could guess

and it is not good it is this value here

and the problem is that the compiler is

silently putting in a garbage value and

not what we want here because virus 3 is

basically not capable of storing

negative numbers so the compiler is

going to do its best and put in a

garbage value and this is not what you

want and you need to be aware of this

this is really all we set out to do in

this lecture i hope you know about

assignments and be careful when you are

doing assignments on variables whose

types are deduced with auto and we're

going to stop here in this lecture in

the next one we're going to try and

recap what we saw in this chapter go

and meet me there in this lecture we're

going to recap what we saw in this

chapter and this chapter was really all

about variables and data types we had a

chance to look at different types that

we can use in c plus plus we saw that we

have fundamental types we can use to

represent integers floating points

booleans and we also saw that we can do

type deduction with auto we had a chance

to make it clear that data is

represented in memory as zeros and ones

and that there are some kinds of

transformations we do on these pieces of

data to turn them into a form that is

easily usable and manipulable by humans

and we saw that for integral types or

integers we could do that through number

systems and we had a chance to look at a

few number systems like binary octal and

hexadecimal and we had a chance to play

with all these variable types in visual

studio code and see the nuances of how

you really work with them i would like

to welcome you in this new chapter and

this one we're going to be looking at

operations we can do on our data and

there is a bunch of them we can add

things up we can subtract numbers we can

divide numbers we're going to see all

kinds of crazy operations we can do

on the data all the variables that we

have in our c plus plus program we are

also going to have a chance to look at

how we can format stuff when we print

them out to stdc out and we are going to

be using some utilities from the c plus

plus standard library to do some

operations on our variables this is

going to be a fun chapter i can't wait

to get started let's go in the next

in this lecture we're going to be

looking at some basic operations you can

on the data in your c plus plus program

and we are going to be specifically

looking at addition subtraction dividing

numbers the modulus operator and

multiplying stuff we have seen addition

here we have a simple example we have a

variable called sum and we are

initializing it with two numbers that we

are adding up number one and number two

this is something you can do in your c

plus bus program you can also do

some other things for example we have

another one called other sum and we are

adding up some other numbers and we are

going to collect the result into this

variable and we're going to print these

things out so that you can see them on

your command prompt this is how you can

do addition and we're going to have a

chance to play with this in visual

studio code in a minute we can also do

subtraction we can take a number and do

minus another number like we are doing

here we're going to store the results in

this div variable and we can do some

and down here you see another example in

other diff here we're going to subtract

numbers and store the result in other

def and we are also going to print this

out you can also multiply stuff this is

how you can do this you use this

operator here it is the star operator

and this is an operator that many

programming languages use to do

multiplication you should get familiar

with this and again we print out the

result so that you can see that this is

actually working we can also do division

division for integers is a little tricky

if you are seeing this for the first

we're not going to get fractional

numbers c plus plus is going to try and

figure out how many times it can fit 10

in 31 and we are visualizing this here

so in 31 we can only fit 10 three times

so the result of 31 is going to be three

okay with integer division you're not

going to be getting fractional numbers

this is something you should really

understand we have another operator that

is called modulus operator and this

operator is represented by this

percentage symbol that we are doing here

and the result of this operation here is

after you have done the division of 31

and 10. and here the result is going to

be one and you might be wondering why

this is useful it is going to be useful

and i think we're going to have a chance

to play with this later in the course

but right now you just need to be aware

of this operation and what it does okay

these are the operations we're going to

be learning about and playing with in

this lecture let's head to visual studio

code and actually play with this okay

here we are in our working folder for

this chapter you see that i have

prepared all the lectures we're going to

do in this chapter and i have my c plus

20 template project in place i am going

to do what we have been doing all along

so i am going to take these files and

in the current lecture which is basic

and i am going to paste those in and i

am going to open this folder in visual

studio code so let's do that pretty

quick we are going to close the welcome

screen here and we are going to open our

main cpp file and we are going to remove

things we don't need here the first

thing we want to play with is addition

so we're going to say that and we're

going to declare two end variables we're

going to call this number one and we're

going to put in a two for example

and we're going to do a number two

and we're going to put in a seven why

not and what we can do we can say

result equals number one plus number two

and we're going to store the result of

this operation and the result variable

here so what we can do is say sddcl and

we're going to print the result we can

try and compile this and see the result

and we're going to build with gcc as we

the world is going to go through and if

we run rooster here we're going to see

that the result of our operation is 9.

so this is how you can do addition

you can also do subtraction and here we

know to declare a new variable we're

our result variable here so what we're

going to do here is say subtraction and

equals for example let's take number two

minus number one this is the operation

we want to do this is number two what we

are going to be storing in this result

here is going to be a 5 because we are

taking 7 and subtracting 2. i hope this

makes sense so if we grab this line here

and paste it in here so that we save on

and we're going to run rooster again it

is going to say result is 5 because we

taking 7 minus two here the result is

going to be five we can also do a

subtraction operation that is going to

result in a negative number so for

example we can say result equals

and this is going to give us a negative

number because two minus seven is going

we're going to print that here i'm going

to paste this end because i still have

if i bolt with gcc and run my program

we're going to get -5 as a result of

this operation here this is how you can

do subtraction we can also do

multiplication so let's go down here and

say that and we're going to say result

equals number one multiplied by number

two and this is the operator we used to

do multiplication in programming

languages we're going to put in our

and we're going to world with gcc

and if we run rooster now we're going to

get 14 because we are taking

2 and multiplying that with 7. this is

how you can do multiplication

seven and divide that with two try to

give this a guess based on what we saw

in the slides we're going to go down

here and do division and we're going to

say result equals number two divided by

we're going to try and print this out if

we build this the world is going to go

through and if we run this we're going

so to really make sense of this let's

look at these numbers we are taking

number two and dividing that with number

and because we can't store fractional

numbers in an integer the fractional

part is going to be basically chopped

off and we're going to store a three

only three times i really hope this

makes sense the last operation we're

and it is a way to capture the reminder

of a division operation so we're going

and we're going to say number two and

we're going to say modulus using the

percentage operator here and we're going

and we're going to print the result of

take a look at this here and try to

guess what we're going to be doing what

and we're going to take seven divide

and the reminder of that is going to be

one and that's what we're going to store

in this results variable here and if we

print that we expect to get a one here

this is what modulus does let's build

and build with gcc the world is going to

go through if we run rooster here we're

going to get a one let's do what we used

in the slide so that this really makes

sense we're going to go down here and i

equals 31 modulus 10. this is what we

so we're going to print the result here

and here we are really asking

what is going to be the reminder if we

take 31 and divide that by 10 and that

reminder is going to be stored in this

research variable so here we're also

going to get a one so let's weld with

gcc and we're going to run the program

and we are also going to get a one down

here again the modulus operator can be

hard to understand for beginners but it

is really capturing the reminder of the

division again we can see that here we

are asking how many times can 10 fit in

31 and we visualize this here it can

only fit in three times and the reminder

is going to be this red thing you see

here it's going to be one and when we do

a modulus operation here we are

interested in that reminder and that's

what we're going to be storing in

whatever variable that is capturing the

result of this modules operation

and that's what we basically have here

and this is really all we set out to do

in this lecture now i hope you have a

good understanding of these operations

you can do on integers we have used

integers here but you can really do

these operations on numbers except for

the modulus operator which is really

going to make sense for integral types

you can't really do modulus on floating

points or fractional numbers that's not

going to make any sense at all we're

going to stop here in this lecture in

the next one we're going to learn about

precedence and associativity a very

important concept for your operations in

in this lecture we're going to learn

about precedence and associativity so

what do we mean by precedence and

associativity really what we mean by

this is a set of rules that we can

when we have multiple operators in the

like in the example we have here if they

tell you to evaluate the result of this

if we don't have clear rules to follow

we might have multiple answers and we

want to know which one is right or wrong

for example one might want to do a and b

first and then do c and then do d but

one might want to do e minus f

and do b multiply by c and then do

things in different ways and get

hopefully you are saying that this may

be a big problem what we get from

precedence and associativity is the

rules we can follow to know which

operator we have to do first for example

the multiplication and division operator

have to be done before you do addition

and subtraction and if you want to

evaluate this expression here you're

going to have to do b and c first and

then do d and e once you have those

results then you can do addition and

subtraction but the question remains

what do we do first if we have only

addition and subtraction in an

expiration and we solve that problem

with associativity associativity defines

if you do the operations from the left

and again these things might not make

sense yet we're going to do an example

and you're going to really see what is

to summarize precedence tells you which

operation you can do first and

associativity is going to tell you in

which direction you're going to go from

the left or from the right and some

operators are going to be left

associative and that means that you're

going to start evaluating them from the

left some operations are going to be

right associative and you're going to

start evaluating them from the right and

i am not making these things up there is

actually a c plus plus operator

precedence table that you can consult to

you should do first if you really are

evaluating this thing with your mind

okay for example if you look in this

table there are many operators we

haven't seen yet but that's not the

problem the most important thing here is

associativity are and when we get to

learn about these new operators you can

come here and know where they sit in

this precedence table for example we

know how to do addition multiplication

we see that the precedence for

multiplication division and modulus

is higher than for addition and

and we can use this in our operators to

which one is going to be evaluated by

our compiler first another thing i want

you to notice in this table is this

column here on associativity if you go

back to our familiar operators here

these operators are left to right so you

should start evaluating things from left

to right but some operators have right

to left associativity and when we get to

these operators you will start doing

things from right to the left okay i

think it is time we went to visual

studio code and actually played with

this thanks here we are in visual studio

code we are in our working folder we are

going to grab our template projects

we're going to copy this and put that in

our lecture on precedence and

associativity we're going to put that in

here we are going to open this project

in visual studio code we are going to

get rid of things we don't need and

remove this here in the body and we are

going to put in our test code so that we

don't have to type this and save on time

we have a few variables here a through g

and we have an expression here or a

that is combining multiplication

division addition and subtraction and we

have to figure out which operation we're

i would challenge you to do this in your

mind and try to guess what the result is

going to be before we run this in our

compiler we're going to compile this

with gcc and we are going to open our

and if we do durham we're going to see

if we run it we're going to see that the

result is 30. how did we come up with

before addition and subtraction we are

going to take b and c and multiply those

so b and c multiplied we're going to get

a 24 we're going to try and do this in

our brain d divided by a we're going to

so d divided by e we're going to get a 3

so we're going to have a 3 here and

after we have this we're going to do

addition and subtraction so we're going

to take a and add that to the result of

b and c so we're going to say

6 plus 24 which is the result of b and c

we're going to minus the results of d

and e and we're going to do minus here i

hope you are following and then we're

going to minus f and plus g we're going

which is 5. okay so this is our

expression here and now that we have

this we have to think about how we're

going to do this we can try to do this

from the right do two plus five and then

do three minus two plus five and go from

right to left but our associativity

table says that addition and subtraction

have left to right associativity so we

will start from the left so we're going

to do 6 plus 24 we're going to get 30

we're going to minus 3 and we're going

to get 27 we're going to minus 2 we're

going to get 25 we're going to add 5

we're going to get 30. i hope you are

following and we are really following

the rules from our c plus plus operator

precedence table here okay so this is

really how you would use this precedence

and the search activity rules to

evaluate your expressions okay here i

have another example for you so try to

evaluate what we're going to get from

we have a divided by b divided by c plus

d minus e plus f try to do this in your

brain and try to guess what we're going

to get from the compiler if we print

we're going to put in our htdc out

statement here and we're going to try

and build this with gcc of course we're

going to run the rooster and you're

going to get a 24. so how did we come up

with that we're going to start by

division and multiplication and again

where do we start do we do b and c first

or do we do a and b first well we can

check our precedence table here

and we're going to check the

associativity of multiplication and

division we're going to go to this entry

here 13 and we see that it is left to

right associative these operations here

are left to right associative so what

we're going to do we're going to start

from left and go to right so we are

going to take a and divide by b if we

take a divided by b we're going to get a

2 so let's type that here then the

result of that is going to be multiplied

by c and if we go up we're going to see

that c is eight so we're going to

and get six so we can replace this with

then we're going to add d d is nine then

three then we're going to add f which is

a five so we have 16 plus nine this is

going to give us 25 minus three

okay by checking this out i see that i

five it is a two we have here

and if we do this from left to right

because addition and subtraction are

left associative we have to do them from

left to the right we're going to take 16

and add a 9 we're going to get at 25

minus 3 we're going to get 22 plus 2 we

are going to get 24 and that's what we

have here i really hope this makes sense

okay so we have seen how we can use this

but sometimes you want to make it really

clear which operations should be done

and you can do that by using parentheses

around your expressions let's grab the

first expression here and do it again

and put that in place and we're going to

store the result in our result variable

and notice that we are reassigning these

things to the result variable so that we

don't have to declare another variable i

clean and that's what we're doing here

so what we can do here is make it clear

that we want multiplication done first

make it clear that we want the

and when you do this the compiler is

going to see that you want this

operation here done first and that's

what it is going to do and if we print

result again we're going to get exactly

the same thing we had before stdc out

and we're going to put result out and

let's make it clear that we are using

signal which operation we want to be

done first we can compile this with gcc

we're going to run the task to

we're going to see that the result is 30

exactly what we had before but now it is

very clear to the reader of this piece

of code that we want b and c done first

they don't have to go through the

precedence table to really try and

figure this out potentially wasting

precious time another thing you can do

with this is for example what if the

precedence table is not working

according to your needs for example you

done first you can specify this with

parents here and what this is basically

going to do is going to force the

compiler to do this first it's no longer

going to do b multiply by c and d

divided by e it's going to evaluate this

first then it's going to follow the

order in the precedence table that we

have seen before so try to guess what

we're going to get now and i am going to

run the code and we're going to

go through this together so let's run

task and we're going to run rooster now

you see that the result is 72. what is

happening here well let's go through

this line by line we are doing a plus b

9 so we're going to get a nine here

we're going to put that here as a

comment then we're going to multiply

so we're going to do 9 multiply by 8 and

and by that time we're going to be here

and we're going to do the division first

then we're going to take nine and divide

by three that's going to yield the three

so we're going to have a three here

we're going to minus f which is a 2 and

we're going to do plus g which is a 5.

we're going to get 72 minus 3 which is

going to be 69 minus 2 it's going to be

67 plus 2 it's going to be 72 and that's

what we have here hopefully you can see

that using the parents not only can you

make it very clear which operation you

want to be done first you can also

define the rules that are prescribed by

the precedence tables that are defined

in c plus plus i hope this makes sense

and this is really all we set up to do

in this lecture to learn a little more

about precedence and associativity

and my advice to beginning programmers

is not to rely on the president's table

too much it is to try and make your

intent very clear using parenthesis and

anyone reading your code you want to

have to go check these rules in

the reference c plus plus documentation

they are going to directly understand

what your expression is going to do and

that's a good thing readability of your

code is really something you should

strive for this is really all we set out

to do in this lecture i hope you have a

better idea about precedence

and associativity we are going to stop

here in this lecture and the next one

we're going to learn about some cool

things we can do with addition and

go ahead and finish up here and meet me

there in this lecture we're going to be

learning about prefix and postfix

addition and subtraction we have an

example here and it is a simple example

we've seen a lot of times by now we have

a variable value it is an integer and we

have a 5 inside we can add a 1 to it or

we can increment it by one this is

another term we use in programming

incrementing a value we are adding

something to it in this case we are

incrementing it by one and we are

basically going to store a six and this

value here so if we print this out we're

this is what we would expect we are

resetting the value to five and that we

are going to minus one or decrement by

one and the result is going to be saved

in value again so the second stdc out

statement here is going to print a 4.

this is something you should expect

now another thing we can do in c plus

plus is do something like value plus

and what do we mean by that when you use

the first thing you should know is that

this is going to increment by one it's

not going to increment by any other

value c plus plus doesn't provide a way

for you to specify another number to

increment by so value plus plus here is

going to increment by one but another

is that it's not going to increment

directly what's going to happen here if

you look to the top here we have a value

5 when execution hits this stdcl

we are going to grab the value here so

here we're going to really print a 5 but

as soon as this statement is done the

value is going to increment by one so

the next time somebody is going to use

this value here is he's going to find in

a 6 and that's what we have here so the

first one is going to print a five

because we're going to grab the value

in here as is but as soon as we have our

value this is going to increment by one

this is what we mean by this value plus

plus here and the second statement is

going to print sx because it is already

incremented and we call this postfix

increment because plus plus is after the

value here and this is really what this

operator does and sometimes it is going

to come in handy in your c plus plus

applications we can also do the same

thing with minus minus it is going to

grab whatever value we have in this

variable so we have in a five so that's

what we're going to print here

and the next statement is going to find

it already decremented by one because

after we have our five we're going to

decrement by one that's what we are

saying here and we're going to find the

nf4 because 5 decremented by 1 becomes a

4. i really hope this makes sense ok so

what we have seen here is postfix

increment and decrement but we can also

do a prefix version of this thing if you

look at the example we have here we have

and we are saying plus plus value so

this is going to increment the value

directly so as soon as this statement is

executed the plus plus value statement

here we're going to have a 6 inside and

if we print it we're going to get a 6

and this is what you see here if we go

down we are resetting our value and we

so in here we are going to increment the

value before we actually print it here

and we are also going to get a six year

i hope this makes sense and if you have

any problem with this i think if we go

in visual studio code you're going to

have a better way to say this you're

going to see the code running and make

sense of it okay so i think that

now you understand why we're going to

have these numbers printed if we go down

we can do the same thing with

decrementing we have a value here it's

prefix decrement it it's going to be a

four here and if we print it we're going

if you go down here we are resetting

that to five and we are going to prefix

decrement in place and this is also

going to print a four because we have a

five here and if we decrement it by one

we're going to get a four and that's

what we're going to get here okay this

is really all these prefix and postfix

increment and decrement operators are

about we are going to go in visual

studio code and actually see this

running okay here we are in our working

directory we're going to do the usual

we're going to copy code from our

template project we're going to put that

in here we're going to go up and open

this up in visual studio code so we're

going to remove things we don't need and

and we are going to put in the code we

exactly saw in the slides here we have a

value it is an integer and it is five

if we increment it by one we're going to

get a six here okay and if we print it

that's what we're going to get we are

resetting this to five and if we

decrement it by one we're going to get a

so if we run this piece of code we

should have a six here printed out

we're going to bring up our terminal

and build this with gcc the weld is

and if we run the program we're going to

get the value a6 and it is four and this

is really what we expect here okay now

that this is really clear we're going to

go down and play with post fix

i am going to put in a separator here so

that we can clearly see in our terminal

here and we are going to put in our test

code that we are going to use

to play with this let's bring this down

a little bit so that you can see

everything we can remove these things we

don't need them anymore okay we are

going to take the value we had we're

and if we value plus plus here

this is going to be a five because we're

going to capture the value as is so here

but next time we get this value it's

going to already be a sex because we

increment immediately after capturing

the value here so here we're going to

get a 5 and here we're going to get a 6.

and if we go down here we are resetting

our value to 5 before we do any

we are going to capture the value as is

because we are doing post fixed

and here we are going to get a 5 because

we are capturing the value as s

but as soon as we capture our value

we're going to decrement it and the

other statement here is going to get a

decremented value and that's going to be

a 4. so here we're going to print 5 6 5

let's try and build this with gcc

to see that we have no problems we have

no problems the world is good if we try

but uh for this code we just put in here

the value is going to be a 5 and that's

and we're going to get a 6 which is

after we are going to decrement and we

are going to capture the value as is

we're going to get this 5 here and for

the last statement we're going to get a

4 because the value is already

decremented and that's the for we are

i really hope this makes sense and this

the postfix increment and decrement

operators the last thing we want to see

in this lecture is that we can also do

prefix increment and decrementation

we're going to go down here and

set up a place where we're going to be

playing with this so we're going to say

and we are going to put in our code

because i don't want to type all this

that would waste your valuable time but

i do encourage you to type these things

drill them in your brain because that's

how you're going to learn okay let's

bring this down so that we can

understand this piece of code so we are

starting by resetting our value to 5 and

notice here that we do plus plus value

this is going to increment value right

away by this time the value is going to

be six and if we print it out here we're

going to have a six printed down we're

going to reset it to five and then we're

going to implement that in place this is

also going to be printing six and if you

go down we're going to do the same

version of the same thing but we are

going to be decrementing so we're going

to decrement the value that we just

here it's going to become a 4 and that's

what we're going to print and if we go

down here we reset it again to a 5 and

we prefix decrement it in place

so the 5 here is going to become a 4

in here and that's what we're going to

print out if we build and run that's

what we're going to get we're going to

the build is good and if we run our

rooster application the results for the

code we just put in here are just going

and you see that we get a six six this

the other six and for the last two

statements we're going to be getting

fours and that's what we have here i

really hope that now you have a better

idea of this prefix and postfix

increment and decrement operators and

you're going to make use of them when

they really helped you design your

applications better okay so these are

your tools use them when they make sense

another thing that i want to emphasize

here is that these operators only

increment or a decrement by one you

do things in increments of five or seven

or ten they are going to work in

increments or decrements of one we are

going to see a way we can do that with

other operators in the last lecture but

these prefix and postfix operators can't

do that and another thing that some of

you might be wondering about is if we

have the same kind of operators with

multiplication or division and we don't

have those operators in c plus plus

maybe we're going to have them in the

future when they make sense but in the

current version of c plus plus we don't

have them we are going to stop here in

this lecture in the next one we're going

to learn about compound assignment

operators in this lecture we're going to

learn about compound assignment

and these are operators that allow you

to do an arithmetic operation like

addition subtraction multiplication

division and modulus and assign the

result to a value in one go let's look

at an example here we have value here

which is 45 it is an integer and we're

going to print that out but if you go

down here we are doing value plus equal

five and if you look at the comment here

this is equivalent to if you did value

equals value plus five so what this is

going to do it's going to take whatever

value is in this value here it's going

to increment that by five so that's

going to become a 50 and we're going to

store that 50 results back in this

variable here so by this time if we

printed this out we're going to get a

50. again we're going to take the value

it is a 45 we're going to add a 5 it's

going to become a 50 and we're going to

store that result back in this value

variable here it's going to become 50

and if we print here we're going to get

a 50. this is the addition version of

the compound assignment operator we also

have a version for subtraction and we

have an example of that here so it's

going to take whatever value is in this

value variable it is going to find in a

50 we're going to subtract 5 we're going

to get a 45 and that's what we're going

and by the time we hit this stdc out

statement we're going to print a 45.

again we have another version for the

multiplication here so that we can

really play with all these things

we're going to take whatever value is in

here we're going to multiply that by 2

here we're going to get a 90 and that's

what we're going to store back in this

value and if we print here we're going

printed out we're going to go down and

do a version for a division the value is

90 we're going to divide that by 30 and

we're going to store the result back in

value here and we're going to get a 30

stored in here and if we print out

that's what we're going to get here

we also have a modulus version of this

here we have unit 30 we're going to take

it and do modulus 11 and what is the

by 11. the reminder is going to be 8

11 can only fit in 30 two times and

we're going to be left with the knight

30 minus 22 is eight and that's what

we're going to store in the value here

and if we print out that's what we're

if you have trouble understanding this

modulus operator here please go back in

a few lectures back we had a chance to

learn about it make sure you understand

it and then come back here and this is

this is really all compound assignment

is all about we're going to head to

visual studio code and actually play

with us okay here we are in our working

directory we're going to copy our

template project as we always do

and we're going to put that in our

compound assignment operators

we're going to come up and we are going

to open this folder in visual studio

code the project is going to show up in

here and we're going to open our main

cpp file and we are going to remove what

we are going to put in our code so that

we can start exploring this we have a 45

and this variable here which is an

integer if we print it out we're going

we are doing a compound addition

so what we are doing here we're going to

grab whatever value is in this variable

we're going to add a five we're going to

get a 50 and that's what is going to be

and if we print this out we're going to

get a 50. let's put in a terminal here

so that we can see this running and

we're going to run the task to build

executable we're going to get the value

is 50 and that's what we expect here

addition version of our compound

assignment operator and it is really

equivalent to doing this in two steps

saying value equals value plus five

you're going to get the same result if

you do that here actually let's do this

so that you don't think that i am making

this up so let's comment this out and we

equals value plus five and if we build

we're going to see the same thing we can

also go down and run the subtraction

version of this example here here we are

taking the value that we have in here

we are subtracting 5 we're going to get

a 45 and 45 is what we're going to store

that's what we're going to see if we

let's run the test world with gcc

so that our changes are reflected in our

output we're going to run this and we're

going to get a 45 this is what we expect

we are going to go down and do a

multiplication version of this

here we have our compound assignment

statement we are taking whatever value

we have in here which is a 45 we're

going to multiply that by 2 and the

result of that is going to be 90 and

we're going to store that back in value

here and if we print value here we're

going to get a 19. let's build this run

the gcc task and we're going to run our

program and we're going to see that

we're going to see this 90 here we can

go down by a few lines and put in the

code to play with a division version of

again this is going to do really the

same thing only it's going to be doing

this for division we're going to take

whatever value we have in here which is

going to be a 90 we're going to divide

that by 3 we're going to get a 30 and

that 30 results is going to be stored

back in value here and if we print this

out that's what we're going to get

let's build again and the build is going

our program we're going to get a 30. we

are going to go down by a few lines and

put in a modulus version of this we're

going to grab whatever value we have and

this variable here which is going to be

30 we're going to do modulus 11 on that

and that's going to be basically 30

modulus 11. the result of that is going

and we're going to store that result in

value here and if we print that out

that's what we're going to see in this

output statement here we can build again

run with gcc and if we run our rooster

program we're going to get an 8 printed

these compound assignments are about and

why go through the trouble to do

something like this if i can do this

like this well c plus plus gives you

different way to do things different

people have different preferences and

some people me included like to do

things this way because it is compact

and once you use this you're going to

get used to this you're not even going

to think about it in this lecture here i

just wanted you to be aware of this

possibility because you are definitely

going to see it in c plus plus code out

this is really all we set out to do in

this lecture i hope you found it

interesting we are going to stop here in

this lecture in the next one we're going

to learn about relational operators in c

plus plus in this lecture we're going to

learn about relational operators in c

plus plus and these are basically

operators you use to compare stuff let's

look at a piece of code here we have two

numbers one is 45 and another is 60 they

are stored in integer variables number

we can print them out and we're going to

see them on the console or our terminal

and if we go down we can really compare

them we can use the less than operator

greater than greater or equal operator

we can check and see if two numbers are

equal by using two equal signs here be

careful about these two equal signs

because if you use one you're not going

to be comparing numbers you're going to

be taking the thing on the right and

assigning that to the thing on the left

so if you want to compare you're going

to have to type two equal signs another

operator we can use to compare stuff is

exclamation mark and equal which is

going to basically test if two numbers

and we're going to get the result one

thing you should notice here is that we

are wrapping our comparison expression

into parenthesis that's because if we

don't we're going to get a weird

compiler error that i am going to show

you when we get in visual studio code

but we don't have enough tools to really

at this moment so what we are going to

do is avoid that problem by putting

parenthesis around our comparison

expression here we're going to go to

visual studio code and actually see this

in action here we are in our working

directory we're going to grab the code

from our template here and we're going

to put that in the current project which

relational operators we're going to go

in and put in our code and we are going

to open this up in visual studio code

we're going to get rid of things we

don't need here we are going to put in

our code so that we can explore these

things we have two variables in one we

have a 45 in another we have a 60 and

these are integers the name for these

variables are number one and number two

we're going to print them out and we're

going to see them on the console now we

one thing i haven't told you yet is that

these comparison operators evaluate to

booleans in other words they are going

to return true all false if you look

we want to know if number one is less

than number two and the result of that

is whether that's true or false and this

so because of that we are using std bull

alpha here to force sddc out to print

this boolean value here as a true or

false instead of a one or a zero and we

have seen this before so if we try to

build this and run this let's bring up a

and we're going to run the test to build

with gcc if we go down here and run our

rooster program we're going to get our

two numbers 45 and six and we want to

know if number one is less than number

two and that's true 45 is less than 60

so the result of this expression is

going to be true now you know how to use

this operator one thing i want you to

didn't use this parenthesis around this

expression here let's try this out we're

going to remove this parenthesis and

we're going to try and world we're going

to run the task to world with gcc and

we're going to get a really weird error

the compiler is going to try and

evaluate this operator first if we go

back to our c plus plus operator

and look at the operators we are trying

to use in the sddc out statement we're

operator to print fans on the console

has high precedence than our comparison

operators here so the precedence for our

operator to print things to sdd out is

precedence for our comparison operators

is nine and eight so the compiler is

going to try and do this operator first

if we come back in visual studio code

the compiler is going to try and think

that you are printing number one but

then again it's going to see this less

than sign and things are going to blow

up we don't really have enough tools to

understand what is going on right now

but i just don't want you to see this

arrow and show you a way to go around it

and move on with your life by comparing

stuff in your c plus plus programs if

you put parentheses around here the

problem is going to go away let's try

we're going to build with gcc

and everything is going to go back to

normal and we're going to see our output

if we run our rooster program here

this is how you can do this okay now

that we have a basic understanding of

this we can try the other operators and

it is going to be a walk in the park we

are going to go down here and put in our

remaining operators we can use less or

eco operator to test and see if number

one is less or equal to number two we

can use the greater than operator to

test and see if number one is greater

than number two we can use the greater

we can use the equal equal operator to

test that number one is equal to number

two and we can use this operator here

which is made up of the exclamation mark

and an equal sign to test and see

and all these operators are going to

basically saying if what you are testing

for is true or false and we can print

this out and notice that we have this

parenthesis around to avoid the problem

i just showed you a few minutes earlier

and if we run this we're going to see

let's weld this with gcc as usual

we're going to run our program and

you're going to see that number one is

less than number two this is true

number one less or equal to number two

number one greater than a number two 45

is not greater than 60 so this is false

it's not greater than equal so this is

number one equals to number two this is

going to be false and uh the last

statement that is going to test and see

if number one is not equal to number two

is going to evaluate to true because

number one is not equal to number two if

this is not making sense yet please go

through it a couple of times and if you

have a problem please do ask me i will

do the best i can to help you out

another thing i want you to see before i

is that you can store the results of

these operators into a variable and use

that later in your program for example

here we can take our expression to

number one and number two the result of

that is going to be installed in this

and we can print it out later

we're going to build with gcc and we're

we're going to see that 45 equals to 60

is false and it is coming from this

statement here you can try and change

these numbers for example change this to

a 20 and see the results that we get and

you can try and run these in your mind

and see that they really make sense if

we run rooster now we're going to get to

different results because we are now

comparing 45 and 20 and here at the last

statement you see that they are not

equal if we put into equal numbers we're

going to get a true there let's try this

out we're going to run the task to build

with gcc and if we clear so that we get

rid of all this noise and run rooster

20 is equal to 20 and this is true this

is really all we set out to do in this

lecture i hope you have a better idea of

these relational operators in z plus

we're going to stop here in this lecture

in the next lecture we're going to learn

about logical operators in c plus plus

go ahead and finish up here and meet me

there in this lecture we're going to

learn about logical operators these

operators will work on boolean operands

we're going to look at end first to

really make sense of how they work here

is a simple table we can use to try out

the end operation it is going to be

working on two operands a and b

and in the third column here we're going

to have the result so if a is false and

the result is going to be false if a is

false and b is true the result is going

to be false if a is true and b is false

the result is going to be false if a is

true and b is true the result is going

to be true the way you can think about

if any of the operands is false the

result is going to be false and if you

really use this way of understanding

this it is going to be really easy and

the first line here we have a false so

the result is going to be false and the

second line we have a force it's going

to be force in the third line we have a

false the result is going to be false

but in the line number four here we

don't have a false a is true and b is

true so the result is going to be true

and it is going to evaluate to true

if any of the operands is true let's

look at the first line here a is false

and b is false so we don't have a true

the result is going to be false on the

second line we have a true the research

is going to be true on the third line we

have a true the research is going to be

true on line number four we have a true

the result is going to be true and you

don't really have to memorize these

tables if you use these operators long

enough these things are going to be

drilled in your memory if you have any

problem with these operators just look

up tables like this and you can find

whatever it is you need without really

memorizing these things another operator

is the not operator which is going to

negate whatever you give it so if a is

true and we negate that we're going to

get a false if a is false and when you

get to that we're going to get it true

and we use this exfoliation mark to say

that we are negating something if you go

back to or it is denoted by these two

vertical bars and the end operator is

denoted by these two ampersand

symbols here okay now that we know about

these logical tables for these logical

operators we can actually try to use

here we have three boolean variables we

a is true b is false c is true we can

print them out and you see that we are

setting up sddc out to give us the

results in the format of true and false

and down here you see that we are trying

to use the and logical operator

down here you have a and b a and c and

we are doing this on three operators and

chaining these things up so we are

saying a and b and c and let's try and

do this in our mind to see that we

really understand this we have seen that

the end operator evaluates to true

when all operands are true another way

to say this is the end operator

evaluates to false if any of the

operands is false so we're going to end

a and b a is true b is false so the

result is going to be false because we

have a false in here a and c is going to

evaluate to true because a and c are

true a and b and c is going to evaluate

to false because we have a false in here

even if you have 1 000 tools and you end

that with one false that's going to be

dragged down to evaluate to false that's

what we are seeing here we can also do

all operations on these things and

this is going to give you a true if any

is true we know that a is true and b is

false so this is going to evaluate to

true a and c is also going to evaluate

a and b and c is going to evaluate the

so let's go back and see this these are

the values we're going to be using here

we can also try out the nut operator and

it is going to negate whatever we gave

it so if a is true we're going to get a

false b is false we're going to get it

true c is true we're going to get a

false another thing you can do is

combine this logical operators so we can

do something like a and b and all of

and you should notice that we are

wrapping our expressions here in

parenthesis so that we don't have the

same problem we experienced and

explained in the last lecture and one

thing you should know is that for the

compiler to evaluate these things we are

going to follow the rules in our table

for precedence and associativity but we

used parentheses to really make this

easy to follow so we are going to end a

and the result of that is going to be

ored with c and you can try and do this

in your mind and you're going to figure

this out but we're also going to go to

visual studio code in a minute and we're

going to see all these things in action

the last thing you can do is combine

logical and relational operators into

expressions for example here we have d e

and f they are integers and we can print

them out like we are doing here but we

and we're going to end the result of

and we know that these relational

operators evaluate to booleans so we can

use these booleans with logical

operators like we have been doing all

along in this lecture so for example

let's evaluate the first one here in

mind so that you really see what this is

d is 45 e is 20 so d greater than e is

that's also going to evaluate to true so

that's going to evaluate to true and

we are going to go to visual studio code

and actually play with this thanks

okay here we are in our working

directory we're going to jump into our

template project and copy the files we

need and we're going to put them in our

lecture on logical operators we're going

we're going to open up this folder in

visual studio code and it is going to

show up here in visual studio code we're

going to get rid of what we don't need

and we are going to put in the code to

play with these things we have three

boolean variables a is true b is false c

and we can print them out and we're

going to see their values and you see

the setup here so that sddc out is going

to show thanks in the format of true and

false and down here we are ending a few

values we are using the and operator and

it is denoted by these two ampersand

a is true and b is false and c is true

to false because we have a false in here

and again if this doesn't make sense

please do consult the tables for all

these logical operators and all these

things are going to make sense this is

going to evaluate to false because we

have a false in here and a and c we have

true and true so this is going to

a and b and c this is going to evaluate

to false because we have a false in here

remember as soon as you have a false in

your and logical operation you're going

to get a false in your result so we're

going to have a false here we can try

and compile this and see if this is

actually what we expect we're going to

bring up a terminal we're going to use

here and we're going to run the tasks to

and if we run our rooster program we're

going to see that a and b is false

a and c is true this is what we expect

is false and this is what we expect

this is how you can really play with

your and logical operator if you want

you can change things up to really

try and see if they live up to your

now we have changed a to false let's try

and build again we build with gcc

and we're going to run our program

and we're going to get a and b is false

because they are all false a and b are

false so false and false evaluates to

a and c is false because a is false so

we're going to get a false as the result

a and b and c is also going to evaluate

to false okay we have this tension here

let's bring this back to what it was

before so a is going to be true b is

going to be false c is going to be true

and we're going to try and play with the

or operator we are going to go down and

put in code to actually play with this

and it is really nothing special we are

just using the or operator here which is

symbols and or is going to evaluate to

when at least one of the operands is

true okay so we have our values here a

is true b is false c is true a or b is

going to evaluate to true because a is

a or c is going to evaluate to true

a or b or c is going to evaluate to true

because one of these things is true and

we can try and run this we're going to

with gcc and if we run this

we're going to go down here and run

and you're going to see that all these

things are true here because one of

these things is shown and as long as you

have one true operand your or operation

is going to evaluate to true and again

this is following the precedence and

associativity rules we have if we go

back to our table in our browser we're

going to try and look at logical or

left associative so we're going to try

and evaluate this from left to right so

we're going to or a and b and the result

of this is going to be ord with c we

have also seen the not operator which is

denoted by the exclamation mark here and

what it is going to do is basically

flip off or negate whatever it is you

have if you have it true in your

variable the result is going to be false

if you have uniforms the result is going

and not a is going to be false because a

is true not b is going to be true

is going to be false because c is true

as we can see here so let's run the

application and see if this is what we

we're going to run and build with gcc

and we're going to run rooster and we're

going to see that note a is false not b

is true and not c is false and this is

what we expect we have also seen that we

can do combinations of these operators

so for example we can look at the

take a and b this is going to evaluate

we're going to negate this and we're

going to get a true and we're going to

we know that the result of ordering this

with anything is going to be true so we

expect this expression here to evaluate

we're going to see that this is going to

evaluate to true and it is what we

the last thing we want to see in this

lecture is that we can combine

these logical operators with the

relational operators we have seen in the

last lecture we are going to put in a

piece of code to play with this this is

lengthy but you can play with this and

see what this is going to evaluate to to

start you off we are going to do the

first one together so it does test if d

is greater than e and if you look here

45 is greater than 20 so this is going

and we're going to enter that with d

the result of this is going to be true

so we're going to be ending a true and a

true and the result of this is going to

be a true and again you notice that we

are wrapping this in parenthesis to

with the compiler being confused with

what we are trying to print this is

going to get rid of the otherwise ugly

problems we might have to deal with if

we didn't wrap this into parentheses

like this so we expect to see a true

and run the task to build with gcc

and we're going to run rooster and if we

look at the first thing here this is

going to be true and you can try and do

the other ones in your mind as an

exercise and if you have a problem don't

hesitate to ask me i am going to do the

this is really all we set out to do in

this lecture i hope you have a better

understanding of these logical operators

again you don't have to really memorize

them all you have to do is consult the

tables and you're going to basically

know the result of your two operands

depending on the values you have inside

for and or and the not operator we are

going to stop here in this lecture in

the next one we're going to see how we

can format our output to make it really

look better go ahead and finish up here

and meet me there in this lecture we're

going to look at output formatting and c

plus and this is the way we can format

stuff we send it to the terminal through

sddc out and make them show up better as

an example let's say we have a table

and you see that they are cramped and

through output formatting we can take

this and turn this into this

and hopefully we agree that this is

there are a set of tools we can use in c

plus plus and those we're going to be

using in this lecture are going to be

coming from these two libraries ios and

io manip and there are a lot of things

in these two libraries here is a a set

of cards that show a lot of them we are

going to play with a lot of these in

this lecture so you don't have to worry

right now before we start looking at

them i want to bring to your attention

that there is a piece of documentation

on these things the link is here the

and you can open this up and look at

some of the things we're going to talk

about in this lecture okay the first one

we're going to look at is stdendl

this is not new we have been using it

all day long to print out a new line

character so that our htdcl statements

print things on different lines and if

we don't have this manipulator you see

here on the top we have hello and world

and if we print them out they are going

to show up on one line because we are

not separating the lines with std e and

dl down below here we have another way

we can do this we can post a backslash n

after our text and that's going to add a

new line character just like std endl

does okay stdndl and slash n in here

seemingly do the same thing

but they are different but we don't have

enough tools to really understand the

differences right now for now just think

of them as two things that do the same

thing they print out a new character

that allows your text to show up on

different lines like we have hello and

world here okay stdndl is the first

manipulator we're going to play with in

this lecture the next one we're going to

and this is going to send whatever is in

the output buffer to the terminal

and what the heck is an output buffer

let's look at an example suppose we have

sddc out here and we want to print on

this terminal and the message we want to

print is hello world how are you so what

is going to happen if the sddc out

statement is executed things are not

going to be directly sent to the

terminal they are going to go into an

intermediary buffer you can think of

this as some kind of storage in which

data goes before it goes to the terminal

and this is what's going to happen we

print out hello hello is not going to go

it's not going to go to the terminal we

it's not going to go to the terminal and

the data is going to be sent to the

terminal in one go and this may come in

handy in some situations so if you want

the data to go to the terminal directly

you're going to add an sdd flash

after your hddc out statement and we are

going to play with this in a minute in

visual studio code and you're going to

see how this works another manipulator

we have which is really cool is set with

and it is std set w here and what it

does it specifies a width for whatever

text you want to print here we have two

examples the first one is our table that

is not formatted well and you see we

just print out the data and it is going

to show up like we see here on the right

we can use std set with to set the width

of the text here and for example the

last name here is going to show up in a

field which is 10 characters white this

is what we mean here and we do the same

for the first name and the age and if we

data is going to show up nicely as we

see here and again i hope we agreed that

what we have down below here is much

better than what we had here

which was not formatted with set width

and this is how you use this manipulator

here we can also use what we call

justification to control whether our

data shows up on the right or on the

in the width that is allocated to it for

justification is sdd right so the data

is going to show up to the right in its

respective cells we can also use what we

call internal justification by which if

we are showing a negative number the

sign is going to be left justified so it

is going to show up on the left but the

data is going to be right justified and

this may come in handy if you want to

in your terminal we can also use std set

field to specify the field character in

our empty spaces for example here we set

the dash as a field character and the

result is what you see down below here

we have seen std ball alpha and its

stdc out to show boolean output in the

form of true and false if you don't put

this manipulator in you're going to see

those pieces of data as ones and zeros

so for example here we have two

variables condition and other condition

if we print them out they are going to

show up as one and zero we are going to

set our manipulator here so the data is

going to show up as true and false we

can disable this manipulator here with

std noble alpha and the data is going to

go back to be shown in the form of one

and zero this is what this manipulator

does we also have one to show the

positive sign for positive numbers

if we don't enable it the data here is

going to show up like this 34 and minus

45 you see that the minus sign is going

to be shown regardless of the setting

you have for this manipulator but if we

we're going to show the positive number

and this may make sense for whatever

application you might be doing

we can disable this with std no show

posts and after we do this the data is

going to show up in its default format

that we have seen before this is how you

use std show posts we also have

the base in which the data is shown and

we can show the data either in a decimal

in octo or in hexodecimal if you look at

the data here we have an integer which

is positive we have an integer which is

negative and we have a double variable

here and we have some data n for us to

play with we're going to show our

positive integer in these three bases

and the result is what you see here and

this should be no surprise you already

these number systems and how they work

we can take the negative number and also

show it in different bases decimal

hexadecimal and octo and it is what you

have on the right here in our terminal

a double or a floating point number in

these bases the result is not going to

change because these number systems have

no effect on floating point numbers if

you remember we have seen that floating

are represented in memory following

another protocol that is really advanced

a course like this so we are just going

to use this but we're not going to try

and understand it because it is out of

scope for what we are doing here we can

to show the base of our output

so here we have a positive number which

is an integer and we can show it in

decimal hex and act and we're going to

see what we see here to the right but we

can choose to also show the base of

whatever it is we output if we want to

specify that the output is in decimal

we're going to say that here but we can

also decide to show the base and we

enable that with std show base like this

and if we do this we're going to see

decimal is not going to have anything in

front hex is going to have a 0x in front

oct is going to have a zero in front and

by this it is going to be very easy to

the base in which your data is displayed

we can also use std upper case for the

data we print out to be shown in

uppercase where it makes sense for

example here we are trying to print

numbers in hexadecimal here in the

middle so if we don't use uppercase

the number is going to show up like this

you see a and f are lowercase but if we

enable uppercase we're going to see this

in uppercase and sometimes this is going

to be helpful for whatever application

you are using the sun we also have a few

manipulators to control how floating

point data is shown on the terminal and

the two of these are std scientific and

sdd fixed by default stdc out is going

in scientific format where necessary and

it is going to use fixed by default so

and if we just print them out they are

going to show up in this format here if

we use fixed we're going to force the

output to be in fixed format and you're

going to see that the third number in c

here is going to show up as 0.0 and a

few zeros after that because in the

precision that we have now we can't

really show a number that is as low as

we have here in c again we have seen

this scientific format this is

multiplied by 10 to the power of minus

10 and this is a really really low

0.000 up to 10 and that's when this

decimal point is going to show so it's a

number that is really close to zero

that's why we are showing it like 0.0

here i hope this makes sense we can also

use scientific notation if we want that

and if we force scientific notation

everything is going to be shown in

scientific notation another thing that i

really want you to be aware of is that

there is no official way to set

floating point output to its defaults

and here is a hack i actually learned

about when i was making this course the

explanation of this is really out of

scope for this course but just use this

the floating point output format to the

defaults and if you do this you're going

here with the defaults you're going to

see that it is the same things the next

thing we're going to look at is std set

precision which we have seen before and

this is going to set the precision

with which the data is going to show up

on the terminal if you use a precision

of 10 that's what you're going to get

here here you see that we have a double

number it is a number that has a lot of

numbers after the decimal point if we

show it by default it's going to show up

like this the precision is going to be

sex we can increase the precision to 10

to 20 and 50 and it is going to show up

at whatever precision that you specify

please know that this precision is going

to be limited by the type of this a

if it is a floating point the precision

is going to be something like 7 we have

seen that if it is a double the

precision is going to basically double

to something like 15 and if you have a

long double the precision is going to be

something bigger than double but it

can't go below that of a double we have

seen this before we also have show point

showing the decimal point for floating

point values you see here we have a 12.0

this is the most important piece of data

if we don't do show point this is going

to show up as 12 in the output here but

we can use show point to force for the

decimal point to be shown and you see

12.00 here is shown another side effect

show point is going to force the showing

of trailing zeros and it is what we see

here in d e and f we have seen a lot of

manipulators here is a table that is

going to show where many of these are

going to be living so if you need to use

set width this is going to be living

in the i o manip header and here we have

a few other ones so if you want to use a

few of these things these are the

libraries that you will need to include

with pound include as we have been

including i o stream and again the

documentation for these things is shown

cppreference.com this is the exact link

and you can check this out if it helps

now that we have an idea about these

things we're going to go in visual

studio code and actually see these in

action okay here we are in visual studio

code the project we're going to be

working on here is output formatting so

and put those in our project here

and we're going to go up again and open

up this folder in visual studio code

let's do that we're going to close the

welcome screen here and we're going to

remove whatever it is we don't need

and we are going to put in the first

code we want to play with and this is

you don't really need a lot of

explanations for this because we've used

if you don't put it out the data is

going to show up on one line and uh

you're going to have hello world on one

if we put stdndl like this we're going

to have the data show up on different

lines so we're going to have hello and

world on different lines and it is

possible to use a backslash n to achieve

the same thing but these work very

differently underground and we don't

have enough tools to really understand

the difference so for now just take this

as the truth and i know that there are

differences and the most important thing

is that you recognize these things if

you see them in code out there we are

going to bring up our terminum and build

this with our task that is going to

you're going to see that the world is

and that we can run our rooster

binary to see the output you see that we

have hello world on one line

we have hello and world on different

lines and this is a result of these

events we have here you see we have

stdndl this is going to force

the terminal to go to the next line and

print world and after that we're going

to force the terminal to go to the next

line and that's where the next text is

going to show up after that we have

hello and world down here in the

terminal and it is the output generated

by the statements that we have in here

and you can see that it is going to

basically do the same thing as stdendl

but again they work very differently

under the hood okay so this is really

how std endl works and you get access to

it by including the i o stream

library here the next thing we're going

this is going to flash the output buffer

to its final destination and that's

the terminal in this case and if we add

this is going to be directly sent to the

terminal and this may come in handy in

some applications if we run this we're

not going to really see a difference but

underground under the hood the data is

directly sent to the terminal and we had

the chance to explain this in the slides

earlier we can work this program and i

see it running the world is going to go

through if we run the rooster we're

going to see that this is a nice message

to the terminal the next thing we're

going to look at is set with i am going

to put in the code here because i don't

want to type all this and again you can

in the results section of this lecture

you don't really have to type all these

things the most important thing is that

you really understand how they work okay

you see here we are going to use set

with but we haven't really included the

library that is going to give us access

to this and if you don't know which

library you will need to include to get

access to this well you can check the

documentation and to get access to the

documentation you might want to consult

your favorite search engine i am going

to go in google here and type in std

set w and i am going to search and this

is going to come up with a few entries i

am going to click on the one from

cppreference.com because this is

reliable in my opinion and if we open

this up we're going to see that to work

with us you need to include i o my net

so this is what we need to put in visual

studio code to get rid of this problem

let's do that i really wanted you to see

this process you can go through

to know what you need to include we're

going to put this in and hopefully the

arrow is going to go away and we can

focus on studying the effects of these

things here this is going to print and

formatted so the data is going to be

cropped close to each other but we can

format this using set width and if we

pass in a 10 here we are basically

saying last name is going to take the

width of 10 characters even if we don't

really have 10 characters in this so so

you're going to have spaces fill the

remaining spaces so that the data shows

up nicely this is really hard to say in

world so i am going to run this in a

minute so that you can see this but

before we run i want you to see that you

can also store the width information in

a variable like this and i use that

instead in your std statements the

benefit with that is that it is really

easy to change this with if you happen

to change your mind otherwise you would

have to change a lot of things and this

is really bad design i did this to show

you how you can use this but in real

code you are most probably going to

your weft information in a variable and

that way it's going to be really easy to

change and update if you happen to need

that we can build this program with gcc

and if we run it let's bring this up a

little bit we're going to have our data

that is unformatted and you see that it

is really ugly but down below here we

have our formatted table and it is

really nice we have last name first name

and age and it is easier to see these

things we're going to see that it is

force the data to show on the left or to

the right with justification and we're

going to look at code that does that

if we go down here and put in the next

piece of code we want to play with we're

going to see that data is right

justified by default but we have seen

this also you see that gray is cramped

to the right of the width of the cell

for the first name so data is right

justified by default and it is the same

data here and trying to run we're going

to have a better visualization of that

so let's run a little bit we're going to

build the world is going to go through

and if we run this we're going to see

that data is going to show up to the

right gray is to the right woods is to

the right and this is the default

when you set with like this you can also

cause for the data to be left justified

and you do that by coming here and

changing this to left you can do that

but let's keep this in here instead

for your reference and let's put in

another piece of code to justify the

data to the left okay let's go down and

do that we're going to justify the data

to the left and if we print this out the

data here gray should come to the left

and be aligned with the first name here

i hope this makes sense we're going to

run we build with gcc and if we run

rooster gray is going to be justified to

the left this is the meaning of std left

and std right that we just saw and know

that data is justified to the right by

default and it is important to keep the

data is going to be justified to the

right by default the next thing we can

do is to make our data internal

justified and what this is going to do

is make the sign left justified and the

data is going to be right justified and

the best way to save this is really to

so here we have the data it's a negative

floating point number the width is set

to 10 it's going to be right justified

but we are also going to set the

justification to internal and see the

let's weld and run this we're going to

world with gcc and we are going to run

our rooster program and if we look at

the output here you see that if we have

the sign is going to go with the data

whereas if we do internal justification

the sign is going to go to the left and

the data is going to go to the right and

sometimes this is useful depending on

the application that you are welded

especially in applications where you

have to display tabular data on the

console or of the terminal we can also

specify the field character using set

and this is really how it works the data

is going to be left justified but we are

spaces with a dash here and we can bring

this up so that you see the entire thing

but you don't really have to type this

out you can use the code i have provided

in the resources section of this lecture

you can just copy it paste it in here

and use it to play with these things

okay with this our empty spaces are

going to be filled with this dash

let's world and build with gcc we are

going to run this and you're going to

see that we have a field character here

and you can change this basically to

whatever you want if i want i can change

this to a star let's do that and i can

build again if i run this it's going to

be filled with stars right now the next

thing we're going to look at is std bull

alpha we have seen this before but what

it's really going to do is force the

output to be in the format of true and

and the default is in the form of one

and zero here we have a few variables

and that they are of bull type

the first set of stdcl statements here

is going to print in the format of one

and zero we are going to set the output

to both alpha and it is going to be in

the format of true and false and then we

can disable the bull alpha with this

setting here which says hdd no pull

alpha we can vote this and see the

effect of this so we're going to run

rooster again and you're going to see

that condition 1 0 condition true false

condition 1 0 we are able to modify how

our boolean data is displayed on the

console using these two settings here

use them if they make sense for your

application the next thing we're going

to look at is show pose and we're going

we have two numbers positive number

which is 34 a negative number which is

minus 45 and we can decide if we want to

the plus sign for positive numbers by

default the plus sign is going to be

hidden it's not going to be shown if you

want it shown you can use the show pose

manipulator and if you want to disable

that when it was enabled you can use no

show pose and this is going to do what

you want we can build this again and if

we look at the output we're going to see

that post num doesn't have a plus sign

in front because by default the show

pause is disabled and we set the setting

here and we're going to see the plus

sign and if we disable that we're not

going to see the plus sign again this is

the effect of std show posts and std

neutral pose manipulators we can also

affect the base in which the data is

displayed on the terminal and we do this

by setting the output base system

we can set std deck to force the output

std hex to force the output to be in

hexadecimal and std act to force the

output in octal and this is only to take

effect for integral types this is not

going to have effect for floating point

numbers for example here we have a few

variables a positive integer and

negative integer and a floating point

and we're going to try and print these

things in all these base systems we're

print these things in the default format

we're going to see how they look we are

going to take the positive number and

show that in these different number

systems we're going to do the same for

the negative number and we're going to

this doesn't have effect on floating

point numbers because these number

systems don't really work for floating

points we can run this and see the

output we are going to run the task that

is going to build with gcc and we're

going to clear and run rooster and what

we're going to see is that by default

positive number is going to be this

negative number is going to be this and

our double var is going to be this and

we are going to take the positive number

show it in different base systems in

decimal it's going to be like this in

hex it's going to be like this in act

it's going to be like this the negative

in this format here so if we show it in

decimal it's going to be like this hex

it's going to be like this and octo it's

going to be like this you can see that

the double var which is a floating point

is not really affected it's going to be

showing in the same format regardless of

the base that we set here one thing you

should know is that this base setting

here is going to stick so here for

example you see that we have set output

so any other thing that we're going to

print out is going to be shown in octo

and we have to be sure that's what we

want if that's not what we want we will

number system and it's going to take

effect this is how you can use these

different number systems for output in

your terminal we have seen that you can

also force things to show up in

uppercase if that's important for your

application for example here we have a

positive number if we show that in hex

this is going to contain a few

and if we don't set uppercase

it is going to show up in lowercase and

if we want it in uppercase we can set

this setting and it is going to show up

in uppercase this may be helpful in some

applications and i just want you to be

aware of these things we're going to

world and run our application

let's bring this up a little bit so that

we have some breathing room our positive

integer here is going to show up in

lowercase here in hex because this is

going to contain characters and if we

set uppercase you're going to see that

the characters are going to show up in

uppercase and this is the effect of this

setting here we can also affect how

for example here we have a few variables

and by default they are going to show up

with decimal points and use scientific

notation where necessary but we can

fixed for example if that's what we need

in our application and the output is

going to be shown using fixed notation

with decimal points if we want we can

force the scientific format and we do it

like this and all output is going to be

in scientific format and we can disable

all these settings and reset this to the

with this piece of command here there is

set floating point output to the

defaults and this is a hack i actually

learned about when i was preparing the

code for this course and the proper

explanations for this are really out of

scope for this course so if you want to

reset the floating point output format

to the default you're going to use this

but we don't really have enough tools to

understand this yet so just take it by

faith and you're going to see that if we

run this it's going to work let's try

and run this through the compiler and

that the world is going to go through if

we run this and i bring this up a little

bit so that we have a little bit of

breathing room we're going to see that

our double values are a b and c and

that's what we have in our code here and

by default it's not going to be able to

show these things because of the

precision limits so we're going to have

it's going to go up to here and the rest

is going to be chopped off if we use

fixed formats you're going to see that

whatever we had in scientific format

it's going to show up in fixed format

and again this is a really low number

we can force the output to be scientific

and all output is going to be in

down below here we use our hack to set

the defaults and you see that it's going

to go back to the initial format that we

had before this is how you use std fixed

manipulate how your floating point

numbers are printed to the terminal we

have also seen that we can set the

precision of our output in the terminal

here we have a variable a it is of type

double as you can see in a visual studio

code here if you hover over a variable

you're going to be able to see its type

we can choose to see this in whatever

precision we want 6 is the default in

our case here but we can choose to set

the precision to 10 20 or whatever it is

please note that this is going to be

limited by the precision that your type

supports so for example we know that a

double has a precision of 15 and if we

have more than 15 digits in here the

rest is going to be garbage just be

aware of that we're going to try and

build this and we're going to use gcc as

we're going to get our numbers in

different precisions the first one is

using the default which is going to be

if we use 10 we're going to get 10

digits if we use 20 we're going to get

20 digits but if we go over the

precision that our type here supports

we're going to get garbage i hope this

makes sense the last thing we're going

to see is show point and we have seen

outputting the decimal point let's say

that here and a good example for that is

here we're not going to get the decimal

point by default it's going to print 12

but if we go down and force output of

the decimal point here we're going to

and another effect of this is that it's

going to add trailing zeros to fill

whatever space is allocated for your

output variable in the terminal

let's try and run this so that we can

actually see this running we're going to

run our rooster executable and in the

first group here we don't have the

setting for show point and if you look

at the numbers that we had in our code

the first number is 34.1 and you see

that we are padding a lot of numbers

because we had set our precision to a

really big number in the last example

that we have run let's actually go there

and show you that that's why we're

it is really huge but no big deal we can

reset this to whatever we want if this

the important thing here is that we have

34.1 and that's what we are seeing and

if you go to our 12 here you see we have

12.0 but our output is not showing

the decimal point here if it is

important to show the decimal point we

can do std show point here and it is

going to show up this is really what is

important in this piece of code here and

this is really all we set out to do in

this lecture we had a chance to play

with a lot of these manipulators and the

best way to learn about these things is

really to try them out in code

and try to change a few things and see

how that affects the output you get in

the terminal and we had a chance to play

with many of these things in this

lecture there is a lot of these guys i

tried to make this lecture as extensive

as i can that's why it turned out to be

pretty long but once you've learned

about these fans and played with them in

code you're never going to forget them

one last point i want to emphasize again

is that the documentation is of utmost

importance it is really good to come

here and check things out for example if

we go to show point here we are going to

get a nice explanation of what this

manipulator does enables all disables

the unconditional inclusion of the

decimal point character and you can read

and the nice thing is that if you go

down you're going to have a piece of

that you can use to really understand

whatever it is they are talking about

and this is priceless if you are

learning it is a good thing to be able

to use the documentation this is really

all we set out to do in this lecture it

turned out to be really long but i

really hope it was worth it for you

we're going to stop here in this lecture

in the next one we're going to learn

about numeric limits go ahead and finish

up here and meet me there in this

lecture we're going to be playing with a

few functions from this library

specifically we're going to be looking

at the minimum the maximum and the

and this is really how you use them you

can think of this t as a placeholder for

the type for which you want to know the

minimum the maximum and the lowest point

respectively i know this might be

cryptic to some of you so we're going to

look at a few specific examples here we

have a simple explanation of what these

the minimum is going to represent the

that is representable with that floating

point type the maximum is going to be

the maximum floating point number you

can represent and at the lowest number

is going to be the lowest negative

number you can represent with that type

things change a little bit when you

start dealing with integers and these

functions are going to look like this

the minimum is going to be the minimum

number you can represent with that

integer and lowest doesn't really mean

anything for integral types the maximum

is going to be the maximum number one

thing you have to keep in mind is that

the minimum may be negative

if you are using a signed integer if you

are using an unsigned integer for

example for short minimum is going to be

zero and the maximum is going to be the

maximum number representable with that

integer type here we are looking at

numbers for short and but the same story

applies to whatever integer type you are

using even if you happen to be using

long end or end without any modifier

remember that we had to do a lot of

things to get this range and it was

really hard to even do this for floating

point types so this library is helpful

in getting a sense of what we can

represent with the given type b8

floating point or integral let's head to

visual studio code and play with us here

we are in our working folder

we are going to copy code from our

and we are going to go in the current

project which is numeric limits we're

going to go and put in our files

go up again and open this file up in

visual studio code we're going to close

this up open the main cpp file remove

whatever it is we don't need we are

going to include the limits library

remember this is the first thing we need

if we want to play with these facilities

that we just looked at in the slides

and we are going to go down here and put

in the code we want to play with

and it is ridiculously simple

if you have watched the slides we just

did in a minute so what we're going to

be doing here we're going to be printing

out the range for each possible type we

want to play with here so we're going to

say the range for short and is from

and we're going to say std numeric

short that's what we want to deal with

now and we're going to call the minimum

function this is going to give us

the minimum value we can represent with

short and we're going to say std numeric

limits and we're going to call the max

passing in the type for which we want to

and the same story applies for

you see that's the type we are using

here we are also going to play with ant

getting the range we're going to use

to see how these things behave we're

and get to the range and we are also

going to be playing with floating point

types so we're going to compute the

range using the minimum function and the

maximum function and we are going to be

also using the lowest function to see

that this really is the same thing we

described in the slides we're going to

do this for double and long double and

come up in this program what we're going

to do is open up a terminal here we are

going to run the task to build with gcc

and the build is going to be good

and we can go down and run rooster and

we're going to get our values here the

range for short and is from minus 32 768

767 and you see that this is exactly the

same thing we saw in the lecture where

we talked about number systems we saw a

way you can do this manually by plugging

number of digits in some formula that we

came up you can go back and check that

out if you want we do the same for

unsigned short and and then we look at

floating point types we're going to

minimum function to get the start of the

range we're going to get the minimum

positive number we can represent with a

float if we use lowest we're going to

get the lowest minimum number and that

the maximum is going to be the same if

you think this is really small you have

the option to open up this folder in

file explorer and you can open a command

prompt or powershell window by hitting

shift and right clicking and choosing

this option here open powershell window

and you're going to get a bigger window

in which you can type things we're going

to run rooster and we're going to see

things in a much easier way here

this is an option you can use or you can

even use the integrated terminal inside

visual studio code here like we've been

doing all along there are a few other

facilities you can use in this library

of limits for example we can try and

print out if a number is signed or

unsigned or get the number of digits we

can represent in an integer type

these are a few examples i just chose

because they are easy to understand and

really helpful but you can find more

and if you come here at cppreference.com

the link is here you can really find all

about this library here this library

provides a standardized way to carry

various properties of arithmetic types

for example the largest possible value

and we have a bunch of things we can do

here don't be scared of by this template

just think of them as placeholders for

the type for which you are trying to

query information for there are a few

functions you can call on these things

for example there is mean lowest max

that we just played with in visual

studio code but uh you can see that

there are a lot of things you can play

with especially if you have some math

background to understand all these

concepts here you can play with us and

see if it is helpful for whatever

application you are doing okay this is

really all we set out to do in this

lecture to learn a little bit about the

limits library it is helpful in

trying to understand the ranges for your

types if you happen to need these kinds

of things this is going to come in handy

we're going to stop here in this lecture

in the next one we're going to learn

about some math functions we can use in

c plus plus go ahead and finish up here

and meet me there in this lecture we're

going to learn about math functions and

these are functions that are built into

the z plus plus standard library that we

can use to do some math if you are doing

some math operations you're going to

they live in the c math library and if

you want to use them you're just going

to include that and you're going to have

access to them what you see here is a

simple summary of some of the things you

can use in these math functions you can

use std flower to round down or hdd seal

round up you can use the abs function to

compute the absolute value of a number

you can do trigonometry you can do the

cosine sign and things like that you can

compute the exponential of a number

you're going to see what this means in a

few lectures you can use std log and

again if you have some math background

these concepts are not going to be

foreign to you many of these functions

are documented here at cpp reference so

it might be worthwhile to go there and

check what functions are available there

here is an example of something you

might want to do for example you have a

variable it's called weight inside we

have a 7.7 and if you do std floor of

this variable this is going to be

rounded down to a 7. if you want to

round up you're going to use std seal

and you're going to get that and we're

going to see what this is going to give

us in a minute when we hit visual studio

code here is how you would use the

absolute value function you have a few

variables here and if you try to plug

them in this absolute value function

you're basically going to get the weight

of the number without any sign in front

of the number positive or negative the

absolute value is the weight of the

number without caring about the sign if

i may say it like that okay we also have

the x function which is going to compute

the exponential of a number this is a

math concept so if you don't have a

background in math this is going to be a

little hard to wrap your brains around

but in math we have this number which is

and its value is approximately 2.7 18 28

like you see here the exponential

function is going to do what f x here is

doing it's going to take e and elevate

that to the power of x and for example

in our code here we're going to get the

exponential of 10 which is going to be e

elevated to the power of tan and we're

going to play with this in visual studio

code and you're going to see the value

of this we also have the power function

here which is going to take the first

parameter and elevate that to the power

this is going to be 3 to the power of 4

and 9 to the power of 3 and we're going

to get the answer if we plug this into

visual studio code and we have look

functions which is basically the reverse

of the power function that we just

if you do log 8 in base 2 for example

it is like you are asking to which power

and the answer here is going to be a 3

of course but the catch is that the log

function by default works in base e

so what we are asking for example if we

is to which power should we elevate e

to get this number in here and it is

going to be computed and you're going to

see this if you plug this into

visual studio code or you can try to use

one of the calculators available to you

and you're going to see that this makes

sense we also have a special function

that is going to do the same thing but

and this is going to be easier to

understand for example here we are

what we are really saying is to which

to get 10 000 and this is easy because

the answer is a 4 10 to the power of 4

is 10 000 i really hope this makes sense

we also have a square route function we

can use so square out of 81 is going to

we have a function called std round

and uh what it's going to do by default

halfway points are going to be rounded

away from zero so if you have a 2.5 it's

going to be rounded up to a 3 and if you

have 2.4 it's going to be rounded down

to a 2. we also have a host of functions

we can use in trigonometry we have a

sine function we have a cosine function

we have a tan function if you know these

concepts in math this is going to come

in really handy if you want to do this i

have to say that what we just talked

about is a small set of what we can do

with these functions here in c math and

uh we are here at cppreference.com

and we can see all these functions here

we can do reminder we can do f men and

if you want you can check this out in

the documentation for example if you go

to can here and click on it you are

going to get the description and

explanation of what this function does

and you're going to have a simple

example of how you can play with us okay

now i hope you have a better idea of

what we can do with these functions in

the cmat library we're going to head to

and play with some of these functions

here we are in visual studio code the

current project we're going to work on

is math functions we're going to copy

and we're going to put them in our

directory here math functions

and we are going to open this up in

visual studio code and we are going to

remove whatever it is we don't need

and we are going to include our library

and we are going to put in our code so

and here we have a variable called

and we're going to try and use a few

math functions on it so we can use sdd

and std seal to round up so weighted

rounded to floor is going to be printed

out and way to round it to seal is going

we're going to have a number here

in this savings variable it's going to

be a negative number and we're going to

try and compute the absolute value of

this we're going to see it printed out

compute is the exponential of the value

and what this is going to do is going to

and raise it to the power of 10 and

that's what we're going to get printed

here the other thing we want to do here

is compute the power of a number we're

going to take 3 and raise it to the

power of 4 and take 9 and raise it to

the power of 3 and we're going to see

what these things evaluate to we're

going to open up our terminal here and

we're going to run the task to build

with gcc the world is going to be good

and if we run rooster we're going to get

these things here so 7.7 rounded to

floor is going to be seven so we're

going to round down 7.7 rounded to sale

is going to be eight and that's what

we're going to get and the absolute

7.7 because it is a positive number and

the absolute value of minus 5000 is

going to be 5 000. and again when you

compute the absolute value of something

you are interested in the weight of that

thing without considering the sign

without really worrying if it is

positive or negative you just want to

get the magnitude of a number that's

what we use in math to mean that

magnitude okay so if we go down we're

going to get the exponential of 10 is

and you're going to get that here and

again what this function does is take e

and raise it to the power of 10

and that's the answer here we can try

and prove this with a calculator so i am

going to open my windows calculator you

can use whatever calculator you have

i am going to use a scientific

calculator here and you see that we can

hit e and we're going to get the value

of this e number in math here it is

simplified but if i take it and raise it

to the power of 10 the answer is going

and if we look in our program we have 22

26.5 okay it is rounded up a little bit

but it is almost the same thing okay we

also want to play with log functions a

log is basically the reverse of the

and we just talked about this in the

if we do log 18 base 2 we are basically

asking to which power should we raise 2

and the answer to that is going to be

number in base number is going to

evaluate to the catch is that the log

function if you use it row like this it

is going to be using base e and we just

saw that e is 2 to the power of 7 or

something let's go back to our

calculator and see if we can see that

why not why try to guess when we have a

good calculator in our hands we are

using the scientific calculator so if we

we are basically asking to which power

54.59 and the answer is going to be

we have a version of this that is going

to use base 10 so if we use this

we are basically saying to which power

should we raise 10 to get 10 000 and the

answer is going to be printed out here

and it is going to be a four because

this is easy to do in your mind so let's

run this we're going to build the task

we are going to run the task to build

with gcc and we're going to run our

program and uh we're going to get our

54.59 you would elevate e to the power

of this number here this is the answer

and if you want you can prove this with

your favorite calculator you're going to

get something close to this to get 10

000 you'd need to elevate 10 to the

power of 4. that's what we're going to

get in here let's print this out again

many mistakes sorry but i hope you get

the point if we build again so that we

can see things properly and run we're

going to get proper data and this is

really what we expected to get we have a

few more functions we can play with as

let's play with square root and the std

round function here we are going to get

the square root of 81 we're going to get

it printed down and we're going to see

what std round does it is going to

round away from zero if we are at half

point and if we are not at half point if

we are below that we're going to round

down if we are higher than that we're

going to round up we're going to run

this so that you can see this running

and we're going to call rooster and the

2.5 is rounded to 3. 2.4 is rounded to

2. 3.6 is rounded to 4. this is what we

expect and the square root of 81

is 9. this is really all we set out to

do in this lecture to play with a few of

they are not really hard to use once you

have the basics of math nailed down and

again if you want to check the full list

of these functions please come to our

reference documentation here you're

and if you want to see how to use one of

these for example if you click on log 10

here you're going to come here you're

going to get an explanation of the

function and even better you're going to

go down and get a nice piece of code you

can play with and really make sense of

what is happening in these functions

here this is really all we set out to do

in this lecture i hope you found it

interesting we are going to stop here in

this lecture the next one we're going to

learn about some weird integral types

go ahead and finish up here and meet me

there in this lecture we're going to

learn about some weird integral types

and what do i mean by this well if you

look here integral types less than 4

bytes in size don't support arithmetic

operations and these are operations like

addition subtraction multiplication

division you can do these operations on

and here i have an example of some of

those types we have a car it is one byte

is two bytes in size on most processors

so you can't do arithmetic operations if

your integer value is stored in these

why is that well this has to do with

and they decided to choose and as the

integral type for which they can do

these arithmetic operations but

compilers are really smart enough to

notice if you are trying to do

arithmetic operations on these types and

they are going to implicitly convert

and this is something you need to be

aware of if we look at this program here

for example we have var1 and var2 they

are stored in variables that are of type

and we have var 3 var 4 which are stored

in a variable of type car we can try and

print the resizes and we're going to get

two two one one for these variables

occupies two bytes in memory for my

computer here and the car occupies one

byte in memory but the catch is down

the result is not going to be the same

type as defense you added up and you

to deduce to the same type as var one

and it's not resort is going to be an

integer because and is the smallest type

for which we can support these

arithmetic operations so if we print the

size of result one and reserved two

we're going to get four but this is the

behavior you're going to get and we need

to be aware of it the same behavior can

be observed on other operators that we

will have a chance to look at in a few

chapters ahead and these are called

shift operators you use them to shift

bets but i don't want to talk anymore

about them because we're going to have a

chance to learn about them in detail

okay now is time to head to visual

studio code and actually see this in

action here we are in our working

directory we are going to copy our

template project we're going to copy

quickly put that in our folder on weird

integral types this is our current

project here and we're going to open

this up in visual studio code we're

going to open this up and we're going to

open our main cpp file remove whatever

it is we don't need and we are going to

put in our code this must be very

familiar because it is what we just saw

so what we are doing here we have four

variables var one and var two are short

and so these are going to take two bytes

in memory on my computer here and uh car

is going to take up one byte and we're

going to print their sizes we're going

to see them printed down and we are

adding things up here we are taking two

short end variables and adding them up

so what the compiler is going to do it's

going to take this turn it into an end

and then do addition and the result is

going to be an end the same story is

going to happen for reserved 2 here

var 3 is a car so it is one byte in

memory but the compiler can't really add

up integral types which are smaller than

four bytes in memory so what is going to

happen var three is going to be

transformed implicitly behind the scenes

to a net and var four is going to be

transformed to a net and then we're

going to add that up and we're going to

store that in a neat variable which is

if we print this up we're going to see

that size of result 1 and result 2 is a

4 and this is what we expect here and

this is a behavior you need to be aware

of because sometimes your application

logic is going to depend on the size of

data if that's the case you need to care

and if you don't know this you're going

to be beaten by this and it is really

hard to find problems like this

so what we can do is open up our

terminal and we're going to build this

with gcc as we usually do and that we

can run our program rooster and we're

going to see that this is what we expect

var1 is two bytes in size var2 is two

bytes in size wire three and waterfall

are one byte in size but our result is

four bytes because the compiler

our operands here to x to be able to

carry out this arithmetic operation this

is really all we setup to do in this

lecture i hope you found it interesting

we are going to stop here in this

lecture the next one we're going to try

and recap what we saw in the chapter

congratulations on hitting the end of

this chapter and this chapter was really

doing operations and manipulating the

data that you have stored in your

variables the first thing we saw was

that we could do arithmetic operations

on the data we can add things up

multiply divide we also saw the modulus

operator which may seem weird for

beginners but we had a chance to really

play with us after that we learned about

precedence and associativity we saw that

we have to follow to know which

operation to do first if we have

multiple operators in our expression we

also had a chance to learn about prefix

and postfix increment and decrement

operators we had a chance to do compound

assignments things like plus equal minus

equal multiply equal modulus equal now

these things must be making sense to you

we had a chance to look at how we could

compare things using relational

operators like greater than lesser than

and equal or not equal we also had a

chance to look at output formatting and

we saw a host of things we could do to

make data show up better with sddc out

after that we learned about numeric

limits and this is a cool way to know

the ranges for your data types but there

are a host of other properties you can

use in this limits library we learned a

little bit about math functions and we

played with things like the power of

something the exponential the few

rounding functions that we have in the

cmat library and now you must have a

good idea about these functions that you

can use to manipulate and do math on

your variables we ended the chapter by

looking at some weird integral types and

the main message in that lecture was

that you can't do arithmetic operations

on data types whose size is less than 4

bytes in memory if you try to do that

the compiler is going to insert

implicit conversions and if your

application depends on the size of

this is something you need to be careful

about otherwise you're going to have a

finding these problems i would like to

welcome you in this new chapter where

we're going to be learning about a new

way we can do things in c plus plus and

we're going to be doing conditional

programming in other words we're going

to be able to do different things

based on the conditions that we have set

up in our code just to give you an

example here we have a few variables

they are booleans and we have a few

initializers in there red is false green

is true yellow is false police stop is

different things based on discipline

if the light is yellow we might be told

to slow down if the light is green we

might be told to go and do whatever it

is we want to do so we're going to be

able to do these kinds of things and c

plus plus provides different constructs

to be able to do conditional programming

code we just have one of them in this

slide which is this if statement here

this if keyword allows you to do things

like this we have a few others we have

the else keyword we have the switch

keyword we also have a completely

separate operator that is called ternary

operator that allows you to do these

kinds of things and we're going to be

learning about all these things and more

in this chapter we are going to start

and learn about the if statement in the

go ahead and finish up here and meet me

in this lecture we're going to learn

about the if statement and this is a

statement that is going to allow you to

do things based on some condition being

or false here is a simple code example

we have two variables number one and

and we have a statement here that is

going to compare number one and number

two and we're going to store the result

that we have on the left then we're

going to do something based on the value

that we are storing in this result here

if the result in there is true we're

number one is less than number two if

the result is not true we're going to

say number one is not less than

number two and notice in the first if

close year we are testing for the case

where the result is true but sometimes

we need to do something when this

condition here is not true one way to do

that is to negate what we have here

inside the if parenthesis and test for

the reverse of whatever we have in here

if that is making any sense if you look

here we are testing for the case where

if not the result is a true and in other

words we are testing for the case where

the result here is false and we're going

to say number one is not less than

number two this is one way we can go

about this again the if statement is

used to do conditional programming this

is the syntax we use to do it in c plus

plus we say f we put a set of

parentheses and inside the parenthesis

we put the condition we want to test for

and after that we're going to have a

pair of curly braces and what we have

inside these curly braces is going to be

the body of our if statement and it is

basically going to be the code we want

to run if the test here is successful we

can also use an else clause to catch the

case where the test hasn't been

successful in this case we can say if

result equals true we're going to do

and else we're going to do something

else in other words if research is true

we're going to say is less than if it's

not true we're going to say is not less

than and this is a more compact way of

doing what we just did in the slide here

you can also directly use your

expression as a condition and the

requirement here is that the expression

evaluates to something that we can treat

like a boolean because the condition has

to be a boolean it has to be true or

false okay here is another simple

example we have seen this in the last

lecture we have a few variables

containing our conditions and we are

saying if the light is red for example

we're going to do something if it's

yellow we're going to do something if

it's green we're going to do something

we can also nest conditions for example

if statement and inside that if

statement set up other if statements and

if our logic needs something like this

you can do this and you can take

advantage of this to achieve whatever it

is you want to do in this case if the

light is green we're going to

fall in here and we're going to do

another condition so if the light is

green and if the police officer has

stopped you you're going to stop and if

they haven't stopped you you're going to

go because the light is green and you

we can also use logical operators to

kind of achieve the same thing and we

say if the light is green and the police

officer hasn't stopped you you're going

to go else you're going to stop and you

can do something like this and you see

that you can combine the logical

operators we've learned about with the

conditional programming techniques we

are learning about here to do really

powerful stuff and we're going to be

doing this all over the place in the

course so we're going to head over to

visual studio code and play with us here

we are in our working directory we're

going to be working on if statements and

we're going to grab our template project

the template files i should say and

we're going to put them in here

and we're going to open this up in

visual studio code as we always do so

let's do that open folder and we should

fall in here and open our main cpp file

let's do the usual and remove what we

and we are going to put in our code so

that we can really play with us we have

two variables in here number one and

number two they are integers and we have

the values 55 and 60 inside we can do a

comparison between these two variables

and what this comparison is going to

yield is a boolean value that we're

going to store in our boolean variable

here which is called result

and what we can do is use this to do

some conditional programming so we're

going to say if the result is true we're

going to do something and if the result

is not true we're going to do something

else and this is how we say it this

syntax here may be confusing to new

students but try to think of it if not

research is true and that's really the

same thing as saying if result is false

try to stream this in your mind a little

bit and you really are going to

understand okay so now that you have

guess what we're going to see if we run

this what are we going to see on the

console okay give it a try so we're

going to run this in visual studio code

let's open up a terminal first

and we're going to world with gcc as we

we're going to bring this up a little

bit so that we have some breathing room

and we're going to run rooster let's see

what we have here we have reserved

equals true and that's coming from this

and we have freestanding if statement

here and we have our meat of this

program what we really are interested in

we have 55 is less than 60. so our test

here succeeded and we fell in this body

and executed this sddc out statement

that's why we're saying number one is

number two and number one is 55 which is

what we see here and number two is 60

which is what we are seeing here

the second statement here execute you

know it is testing for the case where

not result is true so it's going to

exactly do the reverse of what this test

and if this fails this one is going to

succeed which is what we have now so

what we can do to really play with this

we can go up and change for example

this is going to flip the order of these

numbers if i may say it like that and if

we run it we're going to build with gcc

we're going to see result is false so

result became false because number one

is not less than number two so this is

going to be false and the test here is

going to fail result is not true so

we're not going to go in here and look

at here if not result is true so

if we negate this this is going to

become true and this test here is going

to succeed and we are going to fall in

here take some time to really understand

this and if you have a problem ask me i

am going to do the best i can to help

you out but make sure you understand

this because this is really fundamental

in your journey as a software developer

not just in c plus plus any career as a

software developer you're going to need

to understand this okay what we're going

what we just did here because we're

going to see another way to do this and

we don't want to have noise output in

our terminal this is going to just make

things hard for us to see so what we're

we're going to go down in here and put

the result was commented out we don't

want to comment that out so we're going

to take this out because this is our

condition we're going to grab it and put

that outside our comment section this is

going to do and if we go down again

we're going to click on this file icon

and uh give ourselves some more

breathing room here we don't really need

to see that main cpp file anyway

so if we come here we can use the else

to test for the case where our condition

and if you look here we are essentially

saying the same thing we are saying if

result equals true we're going to fall

in here and else we're going to fall in

here so we don't need to do the double

if statements that we just did

here and this is much more compact and

easy to read let's look again at the

numbers we have here number one is 65

number 2 is 60. this expression here is

going to be false because 65 is not less

than 60 we're going to have a false in

result is going to be false this is

going to fail and we are going to fall

or 65 is not less than 60 which is what

we have in our values so we're going to

build this again and we're going to run

rooster that's clear so that we have

some breathing room we're going to run

rooster and you're going to see that 65

60 which is what we expect again if you

go up and change these numbers to

whatever you want try to change these

numbers to different values to see what

you get as output if we do this we're

going to see that number one is less

than 60 so this is going to be true

and we're going to have a true in this

result variable here if we go down

result is true this test condition here

is going to succeed and we are going to

fall in here let's click in our terminal

and hit enter we're going to run rooster

we're going to see 55 is less than 60

which is what we have here okay now i

hope you have a better idea of how you

can use the else close to make your if

statements really compact and this is

really cool okay another thing i want

not go through a variable like this and

use an expression as a condition

directly c plus plus allows you to do

this so what we're going to do we're

going to comment out what we just did

let's do that i'm going to use a block

comment i hope you know how to use this

and we're going to go down and put in

our code it is exactly the same thing

but we took the expression and put that

in the place of our condition variable

here because this is going to evaluate

to a boolean anyway so we can use this

as a condition and this is something

very legal to do in c plus plus so if we

run this we're going to see let's see

what we have in the numbers i have

by now so 55 number one sixty number two

number one is less than number two this

so the test here is going to succeed and

we are going to fall in here that's what

we're going to say we're going to weld

and i'm going to clear and run rooster

and you're going to see that this is the

output we expect if we change up the

numbers again let's take this and make

it a 75 number one so number one

is less than number two is going to

evaluate to false the test here is going

to fail and we are going to fall in this

block here we're going to fall in the

else close of our test here we're going

55 is that what we have in there it's a

60 but this block here is going to

execute that's the most important thing

so we're going to run this and we're

going to try and clear and run rooster

we're going to get what we expect this

is one way we can do this and it is

really cool let's comment this out and

see another example and if we go down we

the example we saw in the slides which

so what we really want to see here is

that we can nest stuff but before we do

try and use these conditions because it

is just fun so if red is true meaning

that the red light is on we're going to

stop if yellow is true we're going to

slow down if green is true we're going

and if we look at what we have here

red is false green is true false is true

and a police stop is true police stop is

not really being used so green is true

we're going to execute the green

statement here and we're going to say go

that's what we're going to say let's try

we're going to build with gcc

bring this up a little bit so that we

and run rooster and you see that it is

go here you can try and change these

boolean variables to different things

and see what is printed out here this is

a great way to learn but what we really

is nested statements and let's go down

and do that okay again we don't want

what we have on top here to disturb us

comment this out and we are going to go

is if the light is green we should go

but the police officer has the right to

stop us even if the light is green at

least these are the laws in the country

where i leave so we have a variable

called police stop here so if they stop

you even if the light is green you're

going to stop and we're going to see

what we see here so if the light is

green we're going to fall in this body

again and we're going to run this inside

or nested if statement and if the

officer has stopped us we're going to

if they haven't stopped us we're going

to go and go on our merry way this is

what we want to see here and again i

want you to stop for a moment try to run

this through your brain and try to come

up with the value we're going to see

when we run this in visual studio code

we're going to build with gcc

and we're going to run a program and you

the light is green okay so we we should

usually go but the police stop variable

here is also true so if we fall in here

this is going to execute and it is going

to succeed and we are going to say stop

and once this statement executes the

else statement is not going to execute

control is going to fall outside here

and we're going to keep doing whatever

we have outside this if statement here

this is really critical to understand if

block of a statement succeeds all the

others are not going to execute and try

to really understand this okay we have

seen this we can now comment this out

because we have something else i want to

we're going to comment this out and

that's that you can combine the if

statements here or conditional

programming with the logical operators

we have learned about earlier in the

course and do really powerful stuff for

not use this nested statement and do

this in one go like this and i think

this is much cleaner so we're going to

say if the light is green and the police

officer hasn't stopped us we're going to

go and if they have stopped us we're

going to stop and you're going to see

that we're going to get exactly the same

result that we had before but this is

really much more compact so we're going

to run and see the result of this and

and run rooster you're going to see that

they're going to stop us and this is

up again and change up these variables

to really anything you want and see what

you get trying to really understand what

is going on here it is not difficult and

the if statement is really fundamental

to any programming you're going to do so

this is really all we set up to do in

this lecture to learn about conditional

programming using the if statement it is

a powerful thing and you're going to see

it all over your software development

career so make sure you really

understand this but even if it's not

clear now we're going to have a chance

to do many examples and you're going to

really understand what this is all about

we are going to stop here in this

lecture the next one we're going to see

how we can use the else if close

go ahead and finish up here and meet me

there in this lecture we're going to

learn about the else if close that you

can attach to your if statement

and that's going to allow you to test

for several conditions in your if

to really understand this suppose we are

building a drawing application and at

any given moment the user might be using

the pan or the marker or the eraser

already whatever tool that it is we

we need to know which tool is currently

selected by the user and we can do a

piece of logic like this we can have the

tool stored somewhere in our application

and when we get to the moment where we

want to do something for example when

the user clicks with the mouse and they

want to drag and start doing things then

we're going to test for the current tool

if the tool is the pan we're going to

use the settings for the pen if the tool

is the marker we're going to use the

settings of the marker and we're going

one tool that is actually selected as

the current tool by the user and when

you do something like this only one

block in this whole chain of statements

is going to execute so for example if we

have the marker as the current tool the

code inside this block is going to

execute and say active tool is marker

but nothing else in this block is going

to execute after we run this statement

control is going to jump at the end of

this whole chain of if and else if

statements here i really hope you

understand this and uh this is really

this is one of the applications i have

done in one of my advanced course about

qt and c plus qt is a framework that

allows you to do graphical user

interfaces like this and you can build

applications like this so what i did

here is i did the exact same thing that

we have here i had the chain of if and

else if statements and whatever tool

was selected as the current tool was

used to draw things on the canvas here

for example if the current tool was the

pen and the pen is this little pen tool

here if it is active we're going to draw

things like hello world here if we have

the star selected we're going to draw

stars if we have the rectangle selected

we're going to draw rectangles we could

do all kinds of crazy things using this

piece of logic here but it is powerful

stuff and you really have to make sure

you understand this so this is how the

else if clause can really help you the

main thing is to allow you to test for

several different conditions you could

do this with a lot of if statements but

that's not going to be really cool it's

going to be ugly and hard to read this

now that you have an idea about this

we're going to head to visual studio

code and actually see this in action

here we are in our working directory

we're going to grab our template project

pretty quick and we're going to use the

else if project here that's our current

project so we're going to do that and

open this up in visual studio code as we

always do we're going to open this up

we're going to open main cpp and we're

going to remove what we don't need

the first thing i am going to do is to

put in a set of variables that are going

to store our tools and we can do

something like this we have a variable

for pen marker eraser rectangle circle

and ellipse i have to say that this is

not the way to go about this we're going

to learn about another way we can do

this but that's going to be there in the

course when we have enough tools to

understand this for now we're just going

okay 10 is going to represent the pan 20

is going to represent the marker 30 is

going to represent the razor and we can

go on until we hit ellipse which is

represented by 60. now if we go in main

and set up a variable and call it tool

for example and initialize it with

whatever tool we think that the user is

currently using for example we can use

circle and initialize this we can set up

a chain of s and else if statements to

do whatever it is we want to do when

this tool here is selected okay we're

going to go down and put in our code i

don't want to type all this so i'm going

to put this up here and if you want you

resource section the code is going to be

there you can copy it and paste it in

here and do things with that okay we

have a chain of if and else if close is

in here and the first one is going to

test and see if the tool is the pan and

notice that we are using double equal

signs here this is what you use to test

for equality you don't use one equal

sign you have to use two equal signs if

you use one equal sign that's going to

be an assignment and this is going to

always evaluate to true so you don't

want to do that again to test for

equality you're going to use double

equal signs in c plus plus so if the

current tool is the pen we're going to

say active tool span if the current tool

is marker we're going to say that so we

are basically going to do this for all

the tools that our application supports

so what do you think we'll see

when we run this the active tool is

so we should print active tool is circle

let's try this out we're going to open

the terminal so that we can see the

output nicely and we're going to world

with gcc and the build is going to go

through if we run this we're going to

see active tool is circle you can go up

here and change the tool to rectangle

for example if you build again you're

going to see that the correct block of

code is going to be executed we're going

to clear and run rooster active tool is

rectangle if we try to put in something

that doesn't exist let's say let's put

just to mess with our compiler here

we're going to get a compiler error

because that type is not known by

our code here so we're going to get bird

was not declared in this scope we don't

know what it is you have to put in

whatever thing you have declared

beforehand here so if we put in a razor

for example we're going to weld with gcc

the world is going to go through going

to clear run rooster the tool is going

to be eraser and this is exactly what we

expect again the main message in this

lecture is that you can use this else if

close if you have several conditions

that you want to test for just like we

have here and again one of these blocks

is going to execute and once we hit the

end of this chain of if and else if

closes we're going to fall here and code

after that is going to execute so let's

say moving on so that you can really see

this here very clear moving on and if we

bolt this we're going to see only one

block from this whole chain and once one

block executes control is going to go

after all this chain and execute

whatever is after that so we're going to

say moving on after we print that the

active tool is eraser here i think we

try and run this and you see active tool

is razer and moving on so after we print

the code from the eraser block we're not

going to execute rectangle or a circle

or ellipse it's going to jump at the end

of this whole block this is really

super clear and again make sure you

understand the syntax here the else if

statement is followed by a set of

parentheses and inside the parenthesis

we have the condition we want to test

for the condition has to evaluate to

boolean and after that we have the block

of code that we want to execute and this

is really all you have to do to get this

we are going to stop here in this

lecture in the next one we're going to

go ahead and finish up here and meet me

in this lecture we're going to learn

about the switch statement and this is

an alternative way to do what we did

with these else if clauses in the last

lecture basically testing for several

different conditions but it's going to

be in a much more compact way than what

we did in the last lecture we are going

to be using the exact same example we

did in the last lecture and we're going

to look at the switch statement and how

it works in c plus plus and this is how

it works we have our variable which is

going to store the current tool and

inside the parenthesis here we're going

pass the variable that we're going to be

basically switching on or testing the

and inside the block we're going to be

basically testing for each case so we're

going to say if the current tool is the

pan we're going to say case pan we're

going to put a colon in here and we're

going to put the code we want to execute

where the current tool is the pan in

these curly braces here and one thing

you should notice from the start is this

this is a statement that tells c plus

that after we successfully execute a

block of code we're going to jump out of

this switch statement if you omit this

everything after the case that you just

executed is going to execute and that's

not probably going to be what you want

if this is not making sense yet please

bear with me you're going to see it run

in visual studio code and you are going

to understand so what you're going to do

you're going to put all the tools you

want to test for in separate cases you

see here we have marker and after that

you can put a default case that is going

to be matched when nothing has been

matched in whatever it is you have

tested for in this switch block here and

when we run this piece of code we're

going to get exactly the same results

that we had in the last lecture but

hopefully you can see that this is much

more compact than the series of else if

closes that we had in the last lecture

again the break statement is really

useful if you don't put it in c plus

plus is going to be confused and after

you hit your successful case

everything after that is going to be

executed so the break statement is

basically telling c plus plus if you hit

it after a successful case is

jump out of this switch block because

you are done you don't have to do

anything else in here and another thing

you should know is that the condition

which is what we have inside this

parenthesis here can only be an integer

or an enum so basically it can be ant

basically every integral type we have

seen before but it can't be another type

such as string because that doesn't

really make sense so be sure to keep

now that you have an idea about this

switch statement let's head to visual

video code and actually see this in

action here we are in our working folder

the current project is going to be

switch so we're going to grab our

template files and we're going to bring

that in here i'm going to go up a little

bit and open this up in visual studio

code as we always do and we're going to

open up our main file we're going to get

rid of what we don't need we are going

to go outside the main function here and

put in our tools just like in the last

lecture we are using integers each one

is represented by 10 20 30 up to 60 and

these are the tools we have and i don't

think i explained this but we are

flagging them const because we don't

want them to be modifiable we have seen

about const earlier in the course we are

going to jump into main and set up our

variable it's going to be ant and we're

going to call it tool and we're going to

initialize this whatever tool we want

let's use eraser why not and then we're

going to put in our switch block we're

and if i type this you see that visual

studio code is going to give me

intelligence or suggestions on what

thing i could do one cool thing that

visual studio code does is give you

snippets to really help you type things

out so we can click on this and it is

going to auto complete a starter version

of our case and we can type in our

expression here which is going to be

what we're going to be switching over so

we're going to switch over the variable

tool here and we can put in our cases so

in our case we're going to start with

pan which is what we have here so we're

going to say case pan we're going to

uh let's remove this and say pen

a block of code that is going to execute

when the current tool is the pen and

we're going to put that in here let's

to the right a little bit and inside the

block we can say sddc out active tool is

pan okay so after that we're going to

put this break statement if it's not

here we're going to have a problem

because when the current tool is the pan

and this code here executes every case

after that is going to execute and

that's not what we want we have to

remember to put this break statement

here okay so we're going to put in all

our other cases so we're going to copy

and look at the next one it's going to

be marker so we can go on the next line

and put in marker we're going to paste

this in we're going to say marker and

we're going to say active tool is marker

and we can keep doing the same thing

we're going to go download them and

paste this in the next one is going to

be eraser so let's do that we're going

to say eraser and we're going to say

current tool is razer and we're going to

i am doing this live because it really

is important for you to see me type this

otherwise you may be confused because

this is a slightly confusing construct

we have in c plus plus the next one is

rectangle so we're going to use that and

we're going to say current tool is

rectangle the next one is going to be

circle and ellipse so let's do that

we're going to put in circle we're going

to go down and paste this in and bring

and i'm going to say circle and we're

going to go down and put the next one in

which is going to be ellipse and after

that notice that video studio code also

inserted a default block and this is a

block that is going to execute when none

so this is really important so you can

and say no match found okay so we want

to see this print out and we're going to

okay after we do this we should get this

to work and do whatever we were doing in

the last lecture so the current tool is

the block here is going to be matched so

code here is going to execute

after that we're going to meet this

break and what it's really saying is

you have done what you have to do jump

out of this switch block here and we're

going to go to the end of this switch

block and we're going to execute

whatever is after that so just like in

the last lecture we can say moving on

and if we execute the program as we have

it's going to say active tool is razor

and it's going to print moving on

let's bring up the terminal so that we

can really see this and we're going to

build with gcc the world is going to be

good and if we run rooster let's clear a

bit we're going to see that active tool

is a razor and we are moving on this is

really cool and it is exactly the same

in the last lecture but now we are using

a much cleaner construct which switch

provides okay we can try to change the

tool and see that this really works we

why not i'm going to build with gcc the

world is going to go through as you see

here and if we run rooster we're going

to see active tool a circle we are

moving on you can try and change this

however you want if we put in ellipse

and world again we're going to build

with gcc and if we run we're going to

get active tool is pan and moving on why

is that ellipse we are saying active

tool is pen we didn't change that so we

just code a really bad bag here so let's

fix this and we're going to build again

i'm glad i found this so we're going to

and we're going to see active tool is

okay so let's see what could happen

if you forgot your break statement after

your case here so the current tool is

and it is the last thing we have in here

so it's not a good test case

is make the current tool the pen or the

marker let's use marker that's going to

and i am going to remove the break

okay so and i am going to remove all the

bread statements we have until we hit

and we're even going to remove that for

and if we both we're going to build fine

you're going to see that the world was

good but if we run this try to guess

what we're going to get the current

stool is the marker so we should print

and hit the end of the switch block and

do moving on but let's see what we get

did we build let's build again just to

be sure so we're going to run rooster

active tool is marker active thought is

eraser active tool is rectangle we

print every other case after the macro

and if we try to change this for example

not use marker and use eraser let's

change this you're going to see that

and everything after that is also going

to execute and it is not what you want

so let's clear and run rooster you're

going to see eraser rectangle circle

ellipse and no match found so you have

ready to remember to put in this brick

statement i am going to hit ctrl z a

couple of times and bring those in and i

think this is enough we have to hit

again so that marker also has it and if

we run now we're going to get what we

expect let's try to use an eraser again

and if we both again and clear and run

rooster we're going to see active tool

is razer and we are moving on

this is what we expect okay this is

really how you work with a switch

block you have to pass in your

expression or your test case and you

catch each case using this case syntax

here you say case you pass in whatever

it is you want to match and you put a

column and you put your code inside this

block here and remember after each case

you have to add this break otherwise

everything else after this is going to

execute and it is not going to be what

you want before i let you go i want to

show you that you can actually group

these case statements if this is what is

making sense for your application so for

this can be grouped into the group of

and uh put them on different lines

something like this so let's delete this

and we're going to delete the other

case circle just like this and we're

going to say drawing shape i think this

syntax is supported in c plus plus okay

and uh we're going to world with gcc

and the world is going to be good so if

we have a razor which is what we have in

here we're going to say drawing shape

you're going to see drawing shapes

moving on we have grouped different

cases and handles them with one block

and this may come in handy in some

one thing you should keep in mind is

that there are limitations on what you

can use as an expression or a condition

in your switch statement and that has to

be an integer something like ant car

unsigned shorter things like that we

have seen all of these things but it can

also be an enum but enam is something we

haven't learned about yet we will learn

about it later when we have enough tools

to understand that but know about this

so if we can in our project in visual

studio code for example and say

john for example and use this as a

switch condition or expression we have

to include string for this to work so

and include the string library we're

going to do string and if we go down

again and try to do switch and use name

as an expression and take out everything

we have in here and try to compile this

you see that the compiler is not happy

okay it's going to say expression must

have an integral or enum type so this is

not even going to compile this is a

limitation you have and you have to make

sure what you pass as a condition here

is an integer something like ant or car

or other integral types we have learnt

this lecture we're going to learn about

ternary operators and this is an

alternative way to do tests with the if

suppose here we have a variable called

max we have two variables called a and b

and we want to find the maximum between

one easy way we can do this is say if a

is greater than b we're going to store

the maximum in max else then b is going

to be the maximum and we're going to

store that in our maximum value and

we're going to print this out if we do

this we're going to get whatever is the

maximum between a and b to be printed

out on the console and this is going to

work really well but we can also use a

ternary expression and the ternary

and it starts with a pair of parentheses

you're going to put your condition

inside the parenthesis you're going to

follow that with the question mark

you're going to put your option one and

after that you're going to put a column

and option two and because this is a

statement in c plus plus we're going to

end this with a semicolon here is an

using f as we have been doing all along

so we say if condition results equals

option one if condition is false result

is going to be equal to option two and

this is exactly the same thing we are

doing with our ternary expression here

if the condition is true we're going to

take option one and assign that to

result if it's false we're going to take

option two and assign that to resort so

this is really a syntactic sugar or a

shorthand for this thing here and it's

going to make your code shorter and

you're going to see this all over the

in c plus plus code out there so you

familiar with this okay so here is our

example of computing the maximum you see

that we have the same variables max a

and b but we have a one liner that is

going to store the maximum in max and we

and hopefully you can see that this is

shorter and better than this okay one

other thing you should know is that

option one and option two should be of

the same type or at least the types must

be convertible and if that fails you're

going to get a compiler error we can

also do ternary initialization here we

we initialize this to false we can use

initialize our speed variable here we

are basically saying if fast initialize

and we're going to print the speed here

and this is going to work and here you

see that i lied a little bit in my

explanation to make it really obvious

what we had in our ternary expression

you don't have to always wrap your

condition in parenthesis but it makes

the code much cleaner okay now that you

have an idea about distance it's time we

headed to visual studio code and

actually tried this and so for ourselves

okay here we are in our working folder

the current project is ternary operators

we're going to grab our template files

and put those where they belong it is in

this lecture here on ternary operators

and we're going to open this up in

visual studio code as we always do we're

going to open this and we're going to

open main cpp and take out whatever we

don't need we are going to go down and

put in our test code we basically have a

few variables let's kill these spaces so

that our code is not cluttered here and

we're going to print our maximum

and we're going to be using a regular if

we have three variables max a and b we

are saying if a is greater than b

we're going to store the maximum and max

otherwise we're going to store b

and this is going to allow us to print

whatever is the maximum between 35 and

20. if we build this let's bring up a

and we are going to build with gcc as we

always do let's bring this up a little

and run rooster we're going to see that

the maximum is 35 if we put our maximum

we're going to get the maximum steel so

we're going to run this out to build

and we're going to run this clear

max is 200 so we're going to get the

maximum regardless of where it is stored

in a or b this is how our code works but

we can use ternary operators to do the

so what we're going to do here we're

going to comment out our if statement

a ternary version so what we're going to

do we're going to say result equals

and we're going to say a greater than b

we're going to put a question mark to

start of our two options option one is

going to be a because if a is greater

than b then a is going to be the maximum

so we're going to grab a here and if a

then b must be the maximum so we're

going to put that as a second option

here this is what we mean with this

statement and we don't have a variable

called results that's why we have a

problem here we're going to put our

result in max and this should

you see the squiggly lines go away and

we can build this and we're going to get

exactly the same result so this is our

ternary operator if we build this it is

going to go through and if we run this

we're going to get exactly the same

result max is 200 and it is what we

expect okay so take some time and really

make yourself familiar with this syntax

it is really nothing complicated you

just have to make sure your brain is

aware of something like this and you're

going to recognize that everywhere you

see it in code out there okay we have

mentioned that you can't pass types that

are not compatible and the requirement

is that a and b be of the same type

or at least types you can do conversions

between so for example if we try to do

we can't really turn a strength into a

integer and this is going to give us a

compiler error and let's look at the

error we see from visual studio code

operand types are incompatible and and

the const car are not compatible and

they have to be compatible if we ignore

this and go ahead and build we're going

to also see an error from the compiler

and it should be the same error so

question mark and column have different

stands you can really compare so for

example we can take out this string here

and put in a floating point let's put in

a 22.5 and say that this is a fluid

you're going to see that the problem is

going to go away here let's wait for a

minute it's not going away we're going

to build anyway you see the world is

so that we don't have all this clutter

you see problems by the way and if we

both again let's try to do that the

builder is going to go through and if we

max is 22 because we are comparing a and

22 here and the compiler inserted an

implicit conversion from this floating

point to integer that's why we are

so what is the type that's the compiler

really used here okay to make it really

clear what is going on we're not going

use max here let's say auto max one

and see what the compiler is really

so we're going to take this out

and by this we're going to see

what implicit conversion the compiler

really did here because what we had

before we were doing an assignment so

whatever was on the left was being

turned into an integer because we were

doing an implicit conversion from an

assignment so whatever is on the left is

turned into the type of whatever we have

on the left of the assignment i hope you

know this already but if we do things

like this we're going to deduce whatever

is on the left and assign that into max

one so we're going to do so we're going

to see the implicit conversion that the

compiler did in here and it is good to

be able to see things like that it is a

let's see what happens here we're going

to print max one and i'm going to world

with gcc this is going to go through

and we're going to see what is printed

and you're going to see that the

implicit conversion happened from end to

flood and we deduce the flood here in

max one so this is really interesting

one might have thought that we had a

to end but it was actually the reverse

and this is quite interesting this is

really all we set out to do in this

lecture i hope you found it interesting

again make sure you have this syntax

here drilled in your brain because

you're going to be seeing this a lot in

your career as a software developer not

only a c plus plus developer actually

and it is going to be helpful

congratulations on hitting the end of

this chapter this chapter was all about

flow control and we had the chance to

learn about many of the tools that c

plus plus provides to do conditional

programming and we were able to see all

kinds of crazy things we had the chance

to do things like if red is true we're

going to run the code inside if yellow

is true we're going to run code inside

if green is true we're going to run code

inside and you had a chance to play with

those things on many occasions we have

seen that the tools that c plus plus

provides really revolve around these

four things here we have if statements

on this if statements we can do else if

to really do long chains of things where

we do different decisions to do things

in our applications we also saw that

switch is an option if you have several

decisions you can make in your

application and we saw that a ternary

operator can really be used to do

two decisions if you have two decisions

you're going to be able to reduce the

number of lines you used to do these

decisions with to one line and we had a

chance to really look at that in detail

in the lecture on ternary operators this

is really all i had to share in this

chapter i hope you found it interesting

we are going to stop here in this

lecture in the next chapter we're going

to start and learn about loops

go ahead and finish up here and meet me

there in this chapter we're going to be

learning about loops and this is a

construct that is provided by the c plus

plus programming language to allow you

to do repetitive tasks relatively easily

suppose we have a task to print a

we can go down and do it like this and

it is going to work but what if they try

do this 100 times then you're going to

start scratching your head you're going

to type this 100 times and you're going

to run your program and it is going to

work then your manager comes up and they

say i want you to do this 10 000 times

or even 100 000 times and then you're

going to start pulling your hair or

running around breaking vents because

that's impossible to do not to worry

here c plus plus provides a way to do

this relatively easily and we're going

to be learning about ways we can do this

in our program in this chapter the

constructs we're going to be using are

these you see here there is a for loop a

range base for a loop a while loop and

do a while loop and we can make use of

these tools to not go crazy printing a

message one million times because that's

okay so that's what we are up against in

this chapter we're going to be learning

about these loop constructs and you're

going to find that they are really cool

for your application i am excited to be

teaching you this so let's get started

in the next lecture and learn about the

for loop go ahead and finish up here and

meet me there in this lecture we're

going to learn about four loops

for loops are one of the constructs we

have in c plus plus to do repetitive

tasks they allow us to do something like

this much more easily for example we

don't have to type stdc out of c plus

plus 10 times or 100 times we can do

this in less than five lines and you're

going to see how cool this is the syntax

for for loops looks like this and it may

look intimidating for first users but

we're going to break this down we have a

few parts in here the first part is the

iterator which is a variable that we're

going to be using to navigate through

the loop and that variable is this

unsigned int i here we are going to

initialize this to zero and the value we

initialize this with is going to be our

starting value and that's another key

point of any loop any loop is going to

have a starting point we are also going

to have a test which is going to control

when our loop ends for example this loop

is going to start with i equal to zero

it is going to keep doing stuff until

less than 10. as long as i is less than

10 it's going to keep doing whatever it

is we want to do and the first part of

the loop is this plus plus i thing here

and this is an incrementation part

that's how i'm going to call it for

simplicity but at least a part that

keeps changing our iterator to make our

loop move forward after these four

points we are going to have a pair of

curly braces and inside these curly

braces we're going to have the body of

our loop and this is the code we want to

execute multiple times and inside this

loop body we can really do all kinds of

crazy things you're going to see how

cool this is again we have a few parts

with our loop we have our iterator which

is this variable i here we're going to

be initializing this with a value that

denotes where we want our loop to start

we then have a test which is going to

control when the loop is going to end

we're going to have our incrementation

part which is going to allow our loop to

move forward and it's going to be doing

that through incrementation or

decrementation but to make explanation

easier here we're going to call this

part the incrementation part of the loop

after that we're going to have the body

of the loop and it's going to be within

this curly braces and it's going to be

whatever it is we want to execute inside

this loop okay these are the parts of a

loop and you need to keep this in mind

okay now that you know the main parts of

how does it really work let's go through

this and see how it's going to print i

love c plus plus 10 times so when this

code gets executed we're going to start

with i equal to 0 because that's what we

are initializing this value with

after the incrementation part we're

and the test is going to say is i is 0

less than 10 and that's going to be true

so if the test turns out to be true

we're going to jump into the loop body

and if it's false we're going to jump to

the end of the loop and execute whatever

is after our loop this is how it works

so if we jump in for the first time when

i is 0 we're going to print i love c

plus plus for the first time then after

the body is executed we're going to

execute the incrementation part

this is going to make i equal to 1 then

we're going to come back to the test

we're going to say is 1 less than 10

that's going to be true we're going to

come in the body and print i love c plus

plus for the second time after that the

incrementation part is going to run

we're going to have a 2 inside i here 2

is less than 10 this is going to be true

so we're going to follow him the body

again and print i love c plus plus for

the third time we're going to keep doing

this until we hit nine for example if we

increment and get a nine we're going to

form the test and say is nine less than

ten that's going to be true so we're

going to fall in here and print i love c

and after that we're going to run the

incrementation part again this time i is

going to become 10 we're going to do the

test 10 is not less than 10 so the test

and we're going to fall on the outside

of the loop here and by that time we'll

have printed i love c plus plus 10 times

and this is really how a loop works for

the first time we're going to run this

initializer part here to initialize our

iterator which is this value i

and then after that we're going to run

if the test is good if it's successful

we're going to fall in the body we're

going to execute whatever code is in the

body and after that we're going to keep

doing the cycle increment test the body

we hit a point where the test fails and

if the test fails we're going to fall

this for loop here we're going to

execute whatever is after this closing

curly brace and this is how a loop works

i want you to go through this one more

time by printing i love c plus plus and

making sure that this is printed 10

and one thing you should have noticed

now is that we use this test to control

how many times the loop is going to

start for example if we wanted it to run

20 times we would start from zero and

and at 20. and you don't always have to

start from zero you can really start

from anywhere for example you can

initialize i with a value like 30 and

end when i is equal to 55. let's say

that as an example you can really do

anything the main important thing is to

understand how a loop works one thing i

want you to notice is that we are saying

iterators are a common thing in c plus

plus code and they're not just used for

loops like we are doing it here there is

a type we use to do iterators and it

makes our code much more readable and

this event is a representation of some

unsigned and type in your c plus plus

compiler this is going to be different

from compiler to compiler but for

example on my system this is eight bytes

so it has quite a good range of values

you can put in there if we use size t

type to declare our i iterator here

we're going to say something like this

we're going to put our curly braces

we're going to put a semicolon we're

going to put our test and we're going to

put our incrementation part and i think

i really emphasize this but the

parts of our loop inside this

parenthesis are separated by semicolons

like this so we have the iterator

declaration we have a semicolon we have

the test we have a semicolon and we put

our incrementation part and then we go

on and put our curlies and inside we can

do whatever it is we want to do

inside the loop so size t is something

you're going to see a lot make sure you

know what it means remember that it is a

representation of an unsigned and type

so it can only represent positive

numbers and it is used to represent

things like sizes in c plus plus thank

the number of students in a classroom

for example that can never be negative

think about the number of seats in a car

that's something that is always going to

be positive and it won't make sense for

that to be negative so for those kinds

of things we can use size t to represent

the size of those things and you're

going to see how this works in a minute

okay now that you have a pretty good

idea about how a loop works and the main

parts that make it up i want you to know

that you can also do all kinds of crazy

operations inside the body of your loop

for example here we are printing out the

current value of our iterator and we're

going to print the double that we can do

this we can also leave out the curly

braces and this is only valid if we have

one statement we want to run in the loop

so this is going to print this message

here five times because this loop is

going from zero all the way to four it

is going to stop when i stops being less

than five and this is going to be five

times if you go through this you're

going to see that this is going to print

five times you should also know that

this iterator that we are declaring like

this is going to be scoped inside the

body of the loop so you can only use it

inside these curly braces and if you try

to use it outside for example here after

the closing curly braces of the body of

the loop you're going to get a compiler

error again you can only use this

variable i which is our iterator

inside the curlies that mark the

start and the end of our loop body if

you want the iterator to be usable

outside the scope of the for loop you

can do something like this you can

declare your iterator outside the loop

and you can initialize that with

whatever you want and then you can set

up your loop like this you can say for j

and put and your test and your

incrementation part and inside do

whatever it is you want to do in the

body of the look if we do it like this

then j is going to be usable outside of

the loop and we're going to see its

value if we print it out like this so

this is also something you can do

you can even go all crazy and leave out

declaration part if you happen to have

iterator declared outside so if you do

something like this it is also going to

work okay the last thing i want you to

see before we head over to visual studio

code and actually try this out

is that it is a bad thing to hard code

your values in for example you see here

we are saying j less than 10

this is really bad design because every

time you need to change the number of

times that your loop is going to run

you're going to have to hunt for these

loops and change these values and this

may be in a lot of places in your code

so a good thing to do is to put the

value that controls how many times your

loop is going to run in a variable like

this we're going to store that value in

notice that it is of size t because it

is a representation of the size of

things something we don't really want to

be negative and we're going to use this

in our test part of our for loop here

instead of saying j less than 10 we're

going to say j less than count and if we

want to change this we have one point of

control to go and change this value here

and this is really good design you

should do this okay we have talked a lot

about loops it is time we headed over to

visual studio code and actually tried

these things out here we are in visual

studio code the current project is for

loop here we're going to grab the code

and we're going to put that in place

and we're going to open this in visual

studio code so let's do that pretty fast

for loop that's the current project we

selected and we opened this in visual

we're going to open up our main cpp file

which is going to show up here and we're

going to remove things we don't need

so let's remove that okay the first

thing i want you to do is the bad way to

again if we want to print i love c plus

plus 10 times we can do it like this and

if we run the program it's going to work

but this is really bad design because

you would have to copy and paste this

for example a thousand times or even a

hundred thousand of times and that's

really bad so if we bring up our

and build with gcc like we always do

the build is going to go through you see

it's successful we're going to clear and

we're going to run rooster and it's

going to say lfc plus plus 10 times if

you count this it's going to be 10 times

because that's what we're doing here but

this is really bad design you don't want

to do something like this so we're going

and do this better using a for loop

let's say that this is the bad way and

we're going to use for loop which is the

good way sorry so we're going to start

by declaring our iterator so we're going

to say for we're going to say size t

let's use unsigned end to show you that

you can use that and we're going to say

i and we're going to initialize this

and this is going to be the declaration

of our iterator this is the first part

we have in this parenthesis here we're

going to put in a semicolon and put in

loop to run ten times so it's going to

run from zero to nine we're going to

less than ten this is one way you can

understand this after we have our test

incrementation part which is going to

change the iterator to make the loop

move forward and we're going to do that

by incrementing our iterator after that

we're going to put a pair of curly

braces not angle brackets and we're

going to fall inside the body of the

loop this block here delimitated by the

curly braces is the body of the loop and

inside here we're going to put whatever

we want the loop to run so we can go

down here and say i love c plus plus 10

times let's say that but before we do

that let's say i so that we know the

current iteration where we are at

and we're going to put a column and say

i love c plus plus this is going to be

better to follow in the terminal i guess

and we need to put our stream output

operator here for this to make sense to

the compiler and this is our loop now if

we run it we're going to see exactly the

same thing like this but we're going to

have these iterators prepended to the

message so that it becomes easy to

follow this and again how this is going

to work we are going to run our code to

declare and initialize the iterator

after that we're going to do the test we

are going to start with i zero so zero

is less than ten this is going to

succeed we are going to fall in the body

and after that we're going to

print sddc out i love c plus plus and

this is going to be zero we're going to

and we're going to do the test again

we're going to have to do is one less

than 10 the test is going to be

successful so we're going to fall in

here and we're going to print a one

incrementation part again we're going to

run the test and we're going to keep

doing this until we hit a point for

example when we increment this to be a

and after that we're going to run the

test we're going to say is 9 less than

10 the test is going to be successful so

we're going to follow in here and we're

and after that we're going to increment

again we're going to run the

incrementation part and we're going to

make i 10 if we run the test we're going

to say is 10 less than 10 the test here

is going to fail we're going to stop

running the loop all together and we're

going to fall on the outside of the loop

and say loop done let's say that so that

we can see this on the terminal and this

is going to run and print i love c plus

plus 10 times and we expect i to go from

try to run this in your mind

take a piece of paper try to

print this as you fall into the body of

the loop you're going to see that's

exactly what is happening here so what

we're going to do we're going to boil

this again so we're going to run the

the world is good we're going to go down

and run this we're going to clear

and you're going to see that we have

zero i love c plus plus all the way to

nine i love c plus plus our loop is

working exactly the way we want okay so

this is the first step we are able to

run our code a lot of times without

really having to manually do things like

this and the benefit of this is that if

we want this to run for example 100

times all we have to do is change our

is equal to 100 and we're going to stop

less than 100 and if we run this we're

the message from 0 all the way to 99 and

this is pretty cool the torso is going

to be 100 times so let's weld again to

we're going to run this task to weld

run rooster prepare to be amazed run and

it's going to run all the way to 99 we

can change this to even 1 000 or even 10

000 why not we're going to weld again

and we're going to be successful

and run rooster and this is going to go

all the way to 10 000 times we're going

to wait for this to get there

now 3 000 4 000 5000 6000 7000 8000

ten thousand it's going to go all the

way to nine thousand nine hundred ninety

nine and it is going to stop and the

this storping number here okay now we

can see that our loop is really working

fine we don't have to do these hddc out

statements a crazy amount of times okay

and the benefit again is that

regardless of the number of times the

code here is going to run our loop is

going to stay relatively the same it's

just going to be one two three four

lines of code and this is really cool

okay so i think this now makes it very

clear how loops work so we're going to

comment this out and show you another

thing and we're going to show you that

you can use size t to actually

denote the type of your iterator

and it is easy to do that so we're going

to say use size t and for us to be able

to see all this here let's hit this file

icon here to close this pane and we're

going to have a better chance of seeing

our code here so what we want to do

we're going to declare a group we're

going to save for we're not going to say

our design and we're going to say size t

and this is going to be the type of our

iterator we're going to say i we're

going to initialize this with a zero

and we're going to put a semicolon like

we just did we're going to put in the

end test we're going to put in the test

so we're going to say i less than 10

and we are going to increment to put in

place our incrementation part we're

going to fall in the loop we're going to

say stdc out this is the code we want to

run so we're going to put in our

coverage value for the iterator and

we're going to say i love c plus plus

again and we're going to put in our new

line character and if we build and run

this it's going to work and run the same

so that we know when it's done and we're

going to weld and run we're going to

and what we're going to do we're going

and run rooster and this is going to say

i love c plus plus 10 times from 0 to 9.

again the message here is that you can

use size t to represent the type of your

iterators and this is the type that is

even used in the c plus plus standard

library so this is going to be something

people expect from your code if you are

representing sizes in code that should

be compliant with the c plus plus

standard library nothing stops you from

using unsigned it like we do here but

we're just going to follow the

convention from the c plus plus standard

library and use this type here to

and some of you might be wondering how

big is this thing we have the tools to

how big it is so let's do that pretty

fast so we're going to go down here

and say sddc out and we're going to say

size t and we can print this out and

let's say what we are doing here so that

use this code as the reference and if we

print this out we're going to see

the size of this thing on the system

where this code here is going to run

the bolt is going to be good we're going

to go here and clear and run rooster

you're going to see that it is eight

bytes on my system so you're going to

have quite a huge range of numbers you

can put in here because this is going to

okay if you try to put in a negative

number you're going to get an underflow

and we have learned about overflow and

underfloor in the previous chapter

okay so let's comment this out and keep

learning more things about for loops

okay the next thing i really want you to

focus on and learn is the scope of the

iterator and we're going to grab our

as a learning tool so we're going to go

and what we're going to have let's move

this a little bit to the right i think

we can do something like this i am going

to select the entire thing here and hit

tab and it is going to be aligned with

okay so we have our loop it is going to

run 10 times it's going to print i love

what is the scope of this i think here

and the fact is it is scoped inside this

loop here you might have guessed that if

you try to use it outside the loop

you're going to get a compiler arrow

because it is only usable inside the

body of the you can also use it inside

the control part of the loop here but

you can't use it outside the loop so if

you try to print i here for example

you're going to get a compiler error so

let's try and do that and show you how

so if we try to print i here let's say i

to make it clear what we want to print

if we try to do this we're going to get

a compiler error because i is not in

scope it is only in scope inside these

curly braces that show the body part of

our loop okay visual studio code is

showing the problem here it's saying

eyes undefined here so you shouldn't

really do this but if we move on and

ignore the message from visual studio

we're going to get a compiler error and

i don't know what you're doing here i

was not declared in this scope where you

are using it and i think it's even going

to give me a line a number it's going to

tell me 46 that's where you are doing

something wrong and if we go in our code

we're going to see that this is the line

where we are making the mistake so i is

not in scope here we're going to comment

this out and say compiler error i is not

in scope that's what you're going to get

if you try to do this and the main

message is that if you declare your loop

like this ah is only going to be scoped

in the body of the loop and that's the

only place where you can mention its

name and use it if we comment this out

and world again the compiler error is

going to go away you're going to see

that the world is good let's clear so

we're going to build again and show you

that the build is good and uh this is

really cool both finished successfully

okay this is one way we can set up our

loop but there is a way we can make our

iterator usable outside the body of the

loop and we're going to show you how you

can do that next so let's comment this

and we're going to grab the code because

we don't want to type all this again and

we're going to say iterator declared

outside the loop we're going to go down

and we're going to align this nicely

and we're going to take the iterator and

declare it on the outside of the loop so

and we're going to say i and initialize

and we're going to say this very clearly

and we're going to say in our

declaration part of the iterator we're

going to just say i and this is going to

work pretty fine if we build this you're

going to see that the world is good and

if we run this it's going to do the same

thing it's been doing it's going to

print i love c plus plus 10 times and if

you want i usable on the outside of the

loop now you can use it we can grab the

in the last run of our code and put that

out here and we're going to align this a

and if we compile this the book is going

and if we try to run rooster we're going

to see i love c plus 10 times we're

going to say loop done and we're going

to print the value of i and you see that

if we do things like this i is going to

be usable on the outside of the loop

and sometimes these may come in handy

depending on the logic of the

application that you are designing just

know that this is something you can do

okay you can go even crazier and leave

out this iterator declaration part in

your loop all together so you can remove

that and we're going to show you how you

can do that in a minute so let's comment

this out i don't want to remove code

because i want you to have this as a

reference if you need to look at this

later so we're going to say leave out

and what you can do is grab the code we

had before i'm going to grab it

and we're going to paste that in here

and what we're going to do is take out

this eye this can work and you may see

code like this out there in the wild so

we're going to run this task to build

with gcc the world is going to be good

and we're going to clear and run rooster

and it's going to do exactly the same

thing so this is one way you can set up

your loops okay the last thing we need

this test here is using a hard coded

value and if we needed to change this

loop to run for example for a thousand

times we would need to manually hunt for

this line of code change this and this

is really not good design so what is

recommended is to store this value in a

variable and test against that variable

let's comment this out and show you that

and go down and copy this entire thing

i don't think i want to do my loops like

this because this is really unintuitive

most times so i am going to declare my

iterator inside and i'm going to copy

the code that does that here we're going

don't hardcord values okay we're going

and we're going to go down and show you

a better way to do things and again

right now we are hard coding in this

and we can call this value count for

example and we can initialize it with

whatever we want in this case we want to

control our loop to run 10 times so

we're going to put in a 10 and instead

of hard coding and this 10 we're going

and if we build and run it the loop is

going to do exactly the same thing it's

going to print i love c plus plus 10

it's going to do the same thing but now

we have one point of control if we want

this to run for let's say 100 times we

can change the count value to 100 times

and if we both again that's how many

times the loop is going to run and this

is much cleaner so i do recommend you

the values you use in your loops in

variables like this and it's going to

so it's going to run 100 times and this

this is really all we set out to do in

this lecture i hope you found it

i am sorry that this lecture turned out

lengthy because we had a lot of things

to talk about but now i hope you really

know a lot of things about ways you can

use your for loops to make them do

things and again many loops that we're

going to use in our c plus plus code are

going to have five parts we're going to

have an iterator which is going to be a

variable we use to manipulate how a loop

moves forward and does things the

starting point is going to be where the

loop is going to start we're going to

have a test in place which is going to

control when the loop ends and we're

going to have the end point encoded in

that test we're going to have the

incrementation part of the loop which is

going to control how our loop moves

forward and we are going to set up a

pair of curly braces that are going to

contain the body of our loop in this

lecture we're going to learn about while

loops and this is another construct we

have in the c plus plus programming

language to allow us to do repetitive

tasks the syntax for a while loop looks

like this we have five parts in our loop

we have the iterator the starting point

the test the incrementation and the loop

body it's just going to be set up

differently for while loops the iterator

is declared on the outside and you see

here we have unsigned in i which is

exactly the same type of iterator we've

used in the last lecture but know that

you can also use size t here i am just

using unsigned and for this case after

you have your iterator declared you're

going to fall to this part here and say

while open a set of parentheses and

inside you're going to put in your test

after that you're going to open a pair

of curly braces and design them you're

going to put the body of your loop

and you're going to do whatever it is

you want to do in the loop in there and

after your code to do whatever it is you

want to do is executed you're going to

put in your incrementation part after

you code and that's what we have here

and this is the setup we're going to be

using for our while loops again

iterator declared on the outside and we

can initialize it with whatever it is we

then we're going to put in our test it's

going to be within this parenthesis and

after that we're going to set up a pair

of curly braces and inside them we're

going to put whatever code we want to

run in the loop and then we're going to

follow that with our incrementation part

and if we try to run this we're going to

run this line we're going to declare the

iterator i and it's going to start with

zero so the test is going to run and 0

and we're going to succeed and we're

going to run the body here we're going

to say i love c plus plus and after that

we're going to run the incrementation

part i is going to become one we're

going to run the test again so one is

less than 10 we're going to succeed

we're going to fall in print i love c

plus plus we're going to increment again

then we're going to have a 2 in i here

we're going to run the test again we're

going to say is 2 less than 10 that's

going to be true so we're going to be

successful we're going to fall in the

body of the loop we're going to

increment and get a three we're going to

test against our three value three is

less than ten we're going to succeed

we're going to print i love c plus plus

we're going to increment again we're

going to test again and we're going to

say is for less than count or 10 we're

going to be successful and we're going

to keep running until we increment and

get a 9. once we get a 9 we're going to

run the test again and we're going to

say is 9 less than 10 that's going to be

successful so we're going to fall inside

print i love c plus plus we're going to

and if we run the test again i'm going

to say is 10 less than 10 that's going

to fail and we are going to fall on the

outside of the loop and we're going to

run whatever code is on the outside here

this is really how a while loop works

and i hope you can see the similarities

between the for loop we have seen it is

really the same thing we just have

different syntaxes to do these things

okay if you look at these things we

already have the same pieces of

information it is just different

syntaxes that c plus plus provides to do

the same things and sometimes you're

going to find it convenient to use while

loops and sometimes you're going to find

it convenient to use for loops and

you're going to have to decide what

works better for whatever it is you are

working on for now we're going to head

over to visual studio code and try this

out okay here we are in visual studio

code the current project is while loop

we're going to grab our template files

and we're going to go in our project and

and we're going to open this in visual

studio code so let's do that

we're going to open the folder

and we're going to work on while loop

here we are going to open our main cpp

file pretty quick and we're going to get

rid of this and what we're going to do

is remove what we don't need and again

we're going to show you the bad way to

do things you don't really want to do

this manually we want to print i love c

we're going to build let's bring up a

use this when we run thanks and we are

going to world with gcc let's do that

pretty quick the world is good

so we can clear and run rooster and

we're going to have i love c plus

printed out 10 times so what we can do

is comment this out and use a while loop

like we want to do in this lecture here

and as we have seen with the slides

the first thing we need to do is declare

our iterator on the outside so we're

going to say size ti we're going to

and that's going to be our iterator

declaration and we're going to say while

i is less than the value where we want

to stop and again we don't want to hard

code these values and so what we're

const size t and we're going to call

this count and make it uppercase this is

a convention we use to declare constants

in c plus plus but you don't have to

make them uppercase it is just a

convention that is going to make your

code easier to read for other people so

put a 10 in here because we want our

is less than count and we're going to

set up a pair of curly braces and they

the start and the end of the body of a

loop here and inside we're going to put

in whatever code we want the loop to run

multiple times and the code is now very

familiar we're going to say sddc out

current iteration and we're going to say

i love c plus plus sdd endl for our new

line character and after that we will

need to put in our own incrementation

part if you forget that you're going to

get something really bad happen we're

really going to look at that later in

the chapter but for now remember to put

the incrementation part and we're going

to say plus plus i this is really easy

and we're going to say that this is the

and this is going to do what we want but

let's go down here and say that loop is

done when it is done so we're going to

and we're going to say stdendya

and before we run this we're going to go

through it and see how it is going to

work so let's click on this file icon

here to close this pane so that we have

some breathing room i am going to open a

notepad file we're going to use to see

when this loop runs we're going to

initialize the iterator here what we're

going to do is put in a 0 and we are

going to run the test to see if 0 is

less than 10 and the test is going to be

successful so we are going to fall in

0 i love c plus plus so let's say that

here to make this super clear inside the

loop we're going to print this message

zero i love c plus plus and after we

execute this line we're going to

increment i is going to become one we're

going to go up again and run the test

less than count or is 1 less than 10.

the test is going to be successful we're

going to run inside the loop and we're

going to print 1 i love c plus plus

that's what we're going to do here so

and after we do that we're going to run

our incrementation part again

i is going to become two we are going to

run the test we're going to say is 2

less than 10 that's going to be true of

course and we're going to fall in the

body again and say two i love c plus

we're going to increment and we're going

to get a three we're going to run the

test again the test is going to be

successful because three is less than

ten we are going to fall in here and say

three i love c plus plus okay so we can

and we are going to increment to get a

four and the test is going to say is

four less than ten that's going to be

true so we're going to succeed and

following the body again and we're going

to say 4 i love z plus blocks

we're going to keep doing this and we're

going to increment again we're going to

get a 5. the test is going to run again

we're going to say is 5 less than 10

that's going to be true of course and

we're going to run the code to print

we're going to increment again to get a

we're going to run the test we're going

to say is 6 less than 10 that's going to

be true of course again and we're going

to print sets i love c plus plus and

we're going to increment to get a 7

we're going to run the test our iterator

we're going to say is 7 less than count

that's going to be true we're going to

print the message again and say seven i

love c plus plus and we're going to

increment again to get an eight we're

going to say is eight less than and

that's going to be true we're going to

fall in the body and say eight i love c

plus plus we're going to increment to

we're going to run the test against our

nine of course nine is less than ten so

that's going to be true we're going to

fall inside and we're going to say nine

and after that we're going to increment

again and we're going to get a 10.

now if we run the test we're going to

say is 10 less than 10 and that's going

to be false because 10 is not less than

10 and if the test here fails we're not

going to fall in the body of the loop

control is going to fall at the end of

the loop body and we're going to print

loop done that's what we're going to say

done and our loop will have run 10 times

by the time we print this loop down

message here if you count here you see

that the loop is going to run 10 times

and it is going to say i love c plus

plus 10 times which is really what we

want okay i really had to show you this

manually so that you can really see what

is happening but now we can weld and run

this and let the computer do the heavy

duty of running this and showing us all

so the build is going to be successful

we're going to run rooster and it's

going to exactly show the same thing we

just came up in our trusty notepad file

here you see it is the same thing but

the beauty is that we don't have to do

all these crazy computations again what

we can do is we can even change the

count to 100 so it is going to run for

clear and run rooster and is going to do

that 100 times and that's pretty fast

this is really all we had to share with

you in this lecture the main thing is to

learn about the syntax of a while loop

and again notice that we have these five

parts that make up our loop we have an

iterator we have the starting point we

have a test we have the incrementation

part and we have the loop body it is

just set up differently with a while

loop like we can see here in this

lecture we're going to learn about do

while loops and this is yet another

construct we have in c plus plus to do

let's look at the syntax here we have

our declaration of the iterator on the

outside and after that you're going to

say do you're going to put a pair of

curly braces like this you're going to

put whatever code it is you want to run

inside the loop and then you're going to

do your incrementation and after the

closing curly brace you're going to say

while and you're going to put in your

text this is really the structure again

notice that we have those five parts and

declaration of our iterator and we're

going to initialize this in place for

example if we want to do that

fall in the body of the loop

and after that we're going to do the

incrementation after we run the code it

is we want to run in the body of the

loop and then we're going to do the test

later and the special thing about a do

while loop is that it is going to run

first and then you do the test last

this is really something you need to be

careful about make sure that when it

runs it is doing whatever it is you want

to do because the test is going to run

after your code has actually run and you

can tweak this to do whatever it is we

want it to do as we are going to see

when we hit visual studio code in a

minute okay again one thing you need to

keep in mind is that the do while loop

of the loop and then do the check or the

test and that may come in handy in some

of the applications you'll be doing

within your career as a c plus plus

developer okay this is really the syntax

we're going to be using we're going to

head over to visual studio code and play

with us okay here we are in our working

folder the current project is going to

we're going to grab the template files

pretty fast and we are going to put them

in our current project let's open this

and we are going to open this in visual

studio code do while loop is our project

we're going to open this and the main

cpp is opened up so let's remove

whatever it is we don't need and we are

going to show you the bad way to do

things the bad way to do things is

typing your code to do things manually

if you wanted them to be done multiple

times and this is something bad if we

bought this and run we're going to go

that's g brush we're going to run

and we're going to get i love c plus

plus 10 times and you don't want to do

something like this what we want in this

do while loops to solve this problem

we're going to comment this out because

and we're going to go down and set up

our do while loop the first thing we

need to do is to set up the count

because we want to store this in some

variables so we're going to say const

and we're going to put in our value

not 190 we're going to say 10 times

and we're going to set up our iterator

and we're going to say i and initialize

this with our starting point we're going

and what we're going to do is say do

and put a pair of curly braces

and inside this pair of curly braces

we're going to put whatever it is we

multiple times so we want to print i

love c plus plus so that's what we're

put in the current iteration

and we're going to put a column and say

and then we're going to jump to the new

and after that we don't want to forget

our incrementation part so we're going

the part that moves our iterator to the

next step this is going to be the

incrementation and this is going to be

and after the closing brace we need to

so we're going to say while and we're

going to put in our test here and we

want to keep doing this as long as i is

and we're going to put in our closing

now this code is going to run 10 times

but let's go through how it's going to

run so that you can really see

that is happening here okay so when this

code here is run we're going to hit the

initialization line here we're going to

declare i and we're going to put in a 0.

we're going to say do and inside we're

going to print whatever we have in i and

say i love c plus plus so we're going to

say 0 because i is 0 at this point and

we're going to say i love c plus plus

and after that we're going to increment

and we are going to do the test at this

we're going to say is one less than ten

that's going to be successful so we're

and we're going to say 1 i love c plus

let's copy this and print this again so

that we don't have to type this all the

i love c plus and after that we're going

to run the incrementation part again so

we're going to get a 2 inside i we're

going to test and say is 2 less than 10

that's going to be true so we're going

to run the body again and print 2 i love

and we're going to increment to get a

we're going to run the test against our

three is three less than ten that's

going to be true so we're going to fall

in the body again and print three

i love c plus plus let's do that we're

going to do the incrementation we're

going to get a 4 inside this i variable

here we're going to run the test we're

going to say is 4 less than 10 that's

going to be true of course we're going

to say four i love c plus plus when we

we're going to do the implementation and

get a five we're going to do the test

it's five less than ten that's going to

be true so we're going to fall in the

body again and say five i love c plus

we're going to increment again

we're going to get a six the test is

going to run and we're going to say is

that's going to be true again then the

body is going to execute and say

6 i love c plus plus we're going to do

the incrementation and get a 7. we're

going to run the test against our 7 so

we're going to say is 7 less than 10

we are going to fall in the body again

and say 7 i love c plus plus

we are going to do the incrementation we

are going to get 8 we're going to say is

8 less than 10 that's going to be true

we are going to fall in the body again

and say 8 i love c plus plus we're going

to do the incrementation we're going to

get a 9 and we're going to run the test

we're going to say is 9 less than 10

that's going to be true so we're going

to go inside and say 9 i love c plus

and we're going to do the incrementation

again now we're going to get a 10 and

the test is going to say is 10 less than

and that's going to be false now the

and we're going to fall after the while

loop here so if we had a statement here

that said stdc out loop done we would

print that we would go down here and say

and this is what we're going to get if

we run this program and again i

encourage you to try this out in your

mind print this in some file you have on

your computer or you can even use a

regular piece of paper but make sure you

understand the flow we go through to get

this code to run multiple times okay now

that we have done this we can work this

do the heavy work for us and run this

fence multiple times the world is going

to be good so what we're going to do

and run rooster and it's going to say

exactly what we expect i'll have c plus

10 times and then it's going to say

loop done okay one thing i want you to

is that the do while loop runs before it

does the test and this may cause crazy

things happening in your program if

let's say that you wanted this program

not to run and initialize this thing

with a zero for the count so it's going

to run zero times but that's not going

to do what you expect with the do while

it runs things before it does the test

so if you run this program it's not

going to just say loop done it's going

to say i love c plus plus and have zero

value in here and it's going to say loop

that's not going to be probably what you

intended by putting a zero in here you

put a zero in here if you want this code

to run zero times or the code in the

body not to run that's another way to

say that but in this case a do while

loop is not going to do what you expect

because it runs before it does the test

let's build this and show you this

so we're going to go through the world

and run rooster you're going to see that

it's saying zero i love c plus plus loop

done it is running even if we set our

count to zero here so be sure the do

while loop is doing what you want but if

you're going to have no problems and if

you want the rope to actually not do

when you have zero counting here you can

use the while loop or the full look like

i would like to welcome you in this new

where we're going to be learning about

arrays and arrays are a way to

set up collections in our c plus plus

program so far we have been working with

single variables for example you have a

bunch of integer variables you can even

have 10 or 20 variables of integer type

and that's going to be fine but

sometimes you don't want to manage all

these variables it is really desirable

to group all these variables into one

single unity and manage them as one

single entity and we can do something

like this group them together and give

them a name so that we can refer to them

under this name here and c plus plus has

the array construct to help us do this

okay so again if you look in memory how

things are laid out you're going to have

a bunch of zeros and ones for example

here each red defend is a net it is four

bytes in size and it can be used to

represent a net so if we have a bunch of

events like this we might want to group

them together and give them a name and

manipulate them under this name this is

another way to look at what we just

talked about here and again arrays are a

way to do these kinds of things in c

plus plus and we're going to be learning

all about it in this chapter we are

going to stop here in this lecture and

we are going to start and look at how

you can declare and initialize an array

and meet me there in this lecture we're

going to see how we can declare and use

arrays in our c plus plus program and

again arrays are a facility we have in

the c plus plus programming language to

group many variables together and

manipulate them as a single unit for

example here we have a bunch of integers

in memory each of these red things is

going to be four bytes in size so we can

think of it as an integer and we can

group them together and give them an a

we call them scores here and they are

going to be living under that scores

refer to each of these things z plus

plus provides an indexing system so we

cannot use angle brackets like this and

refer to the first of these integers as

zero so we can go from zero all the way

to nine here but your array can even be

bigger than this many times bigger than

this and we're going to see examples of

how we can do that but this is an

example of how you can take many

variables group them under one entity

give them a name and be able to

reference each of these events that are

under that entity and now that the idea

is pretty clear let's see how we can do

this in c plus plus the way to do that

is to say and you have to specify the

type of your collection you have to

specify the name after that and then

you're going to put a pair of angle

brackets like this and inside those

angle brackets you can specify the size

you want that collection to have or that

array to have and after this statement

is run we are basically going to have

something like this in memory we're

going to have 10 integers so if you

count here 0 all the way through 9

that's 10 integers they're going to be

grouped together under one logic entity

that logic entity is going to be called

scores and we can go through that name

to manipulate all these things that are

in this entity okay after your array is

declared and you have space for it in

memory basically something like this we

need a way to read data from at and

we're going to see how we can do that

and it is what we have here for example

if we want to print the first of these

elements we're going to say scores

angle brackets and specify the index of

the first element in that array or that

collection of integers that is called

scores okay one thing you should really

keep in mind is that arrays are indexed

from zero they don't start from one so

the first element is going to live at

index zero it's not going to live at

index one so here scores zero is going

to print the first element and scores

nine is going to print the last element

which happens to be the last in our

collection here of integers okay once

our array is declared it's not going to

have data in it there is going to be

data in but it's not going to be data

that we put in so we can think of this

data basically as garbage another thing

i wanted to bring to your attention is

your array has clear boundaries when we

declare an array like this notice that

we specify 10 as the size of our array

it's only going to have 10 elements

inside and you can see that we have from

index 0 all the way to 9 and inside we

have garbage data but we're going to fix

that in a minute what i want you to see

here is that you can to try and read

outside the bounds of your array

c plus plus is funny in that it allows

you to do that but if you do that you're

going to get weird problems for example

your program would crash or do something

really bad so you shouldn't really do

this be aware of the boundaries of your

array if you try to read the data from

the outside of your balance you may read

garbage data you may even cause failure

of the operating system because you

don't really know whose memory you're

reading it's not going to be memory that

is allocated to your program so array

boundaries are something you need to

keep in mind when working with arrays

okay we just saw that we could read data

from the array using this angle bracket

syntax we can even do that through the

read all the elements in the array and

this is how we could do that and you can

see that the loops we learned about in

are starting to come in handy okay we

have seen how we can read data from the

but what if we want to put something

back in what if we want to write our own

data in an array well the syntax is

pretty much what you would expect we

also use this angle bracket syntax but

we're going to assign data to that

element in the array for example if we

wanted to assign data to the first

element in our array we're going to say

angle brackets 0 and we're going to

assign a 20 in it and we can assign a 21

into the element at index 1 and the 22

in the element at index 2 and if we do

that we're going to have something like

this in our array so index 0 we have a

20 index 1 we have a 21 index 2 we have

a 22 and the rest is still garbage

because we didn't put in our data we can

also write data in a loop for example

here we have our array declared

and we're going to loop around putting

data at different indexes notice that

the index is going to be the current

iteration we are at so this is a common

way to do things in c plus plus and you

need to be familiar with this and after

we put in the data we can read that back

and make sure that it is the actual data

that we put in and we're going to have a

chance to play with this in visual

studio code in a minute so don't worry

if some of these things don't make sense

yet but again the main thing here is

this angle bracket syntax we can use

that to either write data in the element

of the array or read data from the

element of the array and this is the

syntax here scores angle brackets i okay

so far our array has been declared and

we didn't really put in data and there

was junk data inside but there's a way

you can declare an array and put data in

in one single statement and this is how

you would do it here we have another

array it's going to be grouping double

we call the array salaries and we

specify that it's going to be

of size five and we can put these

elements in a comma separated list using

braced initialization like this and it

is going to work if we try to print it

out we're going to see these elements

here and you see that we can read this

using the same syntax we've learned

about salaries we say the array name we

do angle brackets and inside we put the

index of the element we are reading from

and this index is coming from our loop

here and it is going to work you're

going to get this element printed out

this is pretty cool when initializing

you can leave out elements for example

here we have a neat array it is called

families it's going to be of size 5 but

we are just putting in three elements

the rest are going to be initialized to

zero when we do things like this and

this is something you need to be aware

of and we are going to try this out in

visual studio code and you're going to

see that this is actually true it is

possible to also omit the size when you

are declaring your array and the

compiler is going to deduce the size

from the elements that you initialize

your array with for example here we have

in one two three four five six elements

this array is going to have a size of

six and if we print elements we're going

to get those printed out notice here

that we are using a ranged base for loop

hopefully you can see that it is easier

to read data from a collection like this

using a ranged base for loop because we

don't have to set up an iterator

initialize it to do the test do the

incrementation we can just read the

value and use it and be on our merry way

this is pretty cool it is possible to

also declare your array constant and

when you do that you won't be able to

modify elements of that array

that's what it means if you make it

constant you basically want it to stay

constant and you don't want to allow

modifications of your array and we're

going to see this in a minute when we

get in visual studio code the last thing

i want you to see is that you can

actually do operations on the data that

you have stored in an array for example

here we can sum the elements up and

store the result back in our variable

sum and this is something you would do

and it might come in handy in many times

okay one thing i want you to see before

we head over to visual studio code and

play with us is that arrays store

repeat after me arrays store elements of

the same type you can't try and store

variables of different types in an array

i don't even know how you would actually

declare that and if you try and store a

than the type that was declared for the

array you're going to get a compiler

error so this is something you should

keep in mind but it makes sense because

when you declare an array you're going

to be given a bunch of bytes in memory

and those bytes are going to be

collections of data that is of the same

type for example here we have a bunch of

integers again each of these red events

is an integer and if you try to put in

something that is smaller or bigger than

an edge then the compiler is going to be

confused that as to how to read these

text so for arrays to work the types

that you store in the array have to be

the same and they need to be consistent

this is something you should know and if

you try to break this rule you're going

now that you know about arrays we're

going to head over to visual studio code

and play with them a little bit okay

here we are in our working folder the

current chapter is raised the current

project is declaring and using arrays

we're going to grab our template code

and we're going to copy and move the

and we're going to open this thing up in

visual studio code pretty quick we're

going to open up the main cpp file and

and we're going to see how we can

okay the way you do that you say the

name of the arrays and you put these

angle brackets and specify the size of

your array if you want you can put a

space in here it's really not going to

make a difference and you're going to

put a semicolon at the end the moment

this line executes we're going to have

the space for 10 integers allocated to

us in memory and that space is going to

be called scores and we're going to be

able to read data from it or even write

data back into it for now let's see how

we can read the data and it is really

simple we're going to use this angle

bracket syntax that we just saw in the

slides so if we want to read the first

sddc out we want to print it out and

specify the index we want to read from

and we're going to say std endl to move

to the next line if you have this typed

out you're going to see that this is

going to work and it is going to print

whatever is stored in the first element

in this array here and again i want you

to keep in mind the memory structure of

your data when you are working with

arrays so what we're going to print

right now is whatever junk data is in

this first element here okay in here

we're going to say that we haven't

and let's bring up a terminal

so that we can play with us and we're

going to build this with gcc as we

the build is going to be good

and run rooster you see that this is the

junk value we have in here we don't have

useful data in here it's just junk data

because we didn't initialize this array

we can also read the element at location

two and see what we have in there when

you run the program i'm not even sure if

it is guaranteed that you're going to

get the same data if you run the program

multiple times but we don't really care

we know that it is junk data so we can't

what we're going to do is run this

and see the value for the element at

the world is going to be good we're

and we're going to run rooster and

you're going to see that at index 1 we

doing it manually like this is really

time consuming and it is possible to

we know the size of this array so it's a

10. and we can loop around 10 times

pretend each element at each iteration

and the way we do that we're going to

read with that loop and we're going to

and we're going to start from index to

zero this is really important because

arrays are indexed from zero they don't

start from one again this is something

you need to drill in your brain

and we're going to put in our test case

we're going to say i less than 10

because we want to go from 0 through 9

and we are going to increment our

iterator after we do that we're going to

jump into the body of the loop and we

didn't name our iterator that's why

we're having this squiggly line here

let's do that pretty quick we're going

to jump into the body of our loop and we

and we're going to say scores

and we need to be careful about how we

format this because i is not something

we have we're going to be getting that

from our iterator here so we're going to

print it like this and this is going to

squares and we're going to say i that's

going to be our index that we want to

and we're going to say stdendl

and uh because we don't want this to

we're going to comment that out

and we're going to go up and make sure

our comment is nice and neat

and we're going to try and run this and

well we don't have any real data in here

we're going to have some junk data so it

could really be anything we get printed

here so let's build with gcc and we're

going to give ourselves some breathing

room we're going to go down and clear

and run rooster and you see that um this

is really some junk data and if we run

it again let's see that we get the same

it is the same data in here if we want

to have in some reliable data we need to

write in our own data and we're going to

see how we can do that we're going to

see how we can write data into an array

and the syntax is really simple so the

you just say the index for which you

want to write data in and you say scores

and you specify the index let's say zero

and i'm going to put in a 20 for example

we're going to grab the index one the

first element and we're going to put in

and we're going to say scores we're

going to say 2 for index 2 and we're

why not and after we do this we can

print this out or read data with the

loop and make sure that the data we did

and comment this out because we don't

want this to confuse us on the console

and we're going to do that we're going

to come down here and print the data out

let's say what we're doing here and if

we build this we expect to see

that at index 0 1 and 2 we have the

let's build and see we're going to run

the build is going to go through we're

going to clear and run the rooster

and look at this score is a 0 20 score

and our data is actually getting gain

now we're going to see that we can also

write the data using the loop to make it

really easy without us manually doing

for that we're going to copy what we

and we're going to comment what we had

so let's comment this out and we're

and uh print the data again we're going

to put in the code here and before we

print the data we're going to put data

with the loop so the loop is basically

going to be the same thing we're going

ti we're going to initialize this we're

going to say i less than 10 because we

want to loop 10 times we're going to

and we're going to fall in the body of

the loop what we're going to do is write

data at the index of the current

iteration i should say so what we're

going to do we're going to say scores i

and we can really put in anything for

now let's say we want to put an i

multiplied by 10 so we're going to take

the current index multiply it by 10 and

we're going to store that in the index

at the current iteration this is what we

and if we print this out try to think

about what we're going to get here

at index 0 let's put in a 0 to be super

clear here that we are starting from

index 0. at index 0 we're going to take

0 and multiply that with the 10 so we're

going to store 0 at index 0. the loop is

going to run again at index 1 we're

going to take a 1 multiply with 10 we're

going to get it 10 at index 2 we're

going to multiply 2 with a 10 and store

a 20 at index 2 and we're going to keep

10 20 all the way to 90 stored in our

array here so if we print it out we

expect to see 0 10 20 all the way to 90.

let's weld and see that that's actually

what we have in our array we're going to

work successfully let's clear and run

rooster and you see that this is exactly

the same thing we have in our array how

cool is that okay another thing i want

you to see is that we can declare and

in place but before we do that let's say

what we were doing here we were trying

to write data in a loop and we're going

to comment this out because we don't

want a lot of confusing output

in our console and we're going to go

down and put in the data because i don't

want to type all these thanks

so we can declare and initialize an

array in place and the way we do that

the array is going to store doubles now

we can really declare an array of

anything but so far we have seen that we

can do that for ant now let's try a

little bit and show you that you can do

the same thing for double times so we

can declare an array of double types the

size is going to be five and we're going

to initialize that with this data here

so at index zero we're going to have a

12.7 index one a 7.5 index 2 a 13.2

an 8.1 and index 4 and 9.3 and that's

what we're going to have if we print

this out here we have a simple loop to

print it out and it's going to basically

12.7 and it's going to go all the way to

salary 4 and print a 9.3 and this is

if it makes sense for whatever you are

designing with c plus plus we're going

let's clear and run and you see that

this is exactly what we expect okay now

this is super clear the next thing we're

going to see is that if you don't

initialize all the elements in the array

those you leave out are going to be

initialized to zero and we are going to

put in a piece of code to play with that

so here we have an array it's a net

array it's going to be called families

and the size is going to be five but we

are only initializing three elements and

these elements are going to be elements

on the front so elements at index 3 and

4 are going to be left out and they are

going to be initialized to 0 by the

compiler so if we print this out we

expect to get 12 7 5 and 0 0 at

different indexes in this array here

we're going to clear because the build

this is exactly what we expect we have a

12 a 7 and 5 and the last two elements

are initialized to zero and this may

come in handy sometimes okay let's

comment this out another thing we want

to see is that we can actually

omit the size when we are declaring our

and initializing it so here is a simple

example we have an inter array called

class sizes we don't specify the size

but we initialize it and the compiler is

going to deduce the size of this array

from the elements we put in here so if

we put in two elements so it's going to

be of size 2 if we put in 10 elements

it's going to be of size 10 and this is

how this works but if you do something

like this and not to initialize the

array let's take this out for example

you're going to get a compiler error

because the compiler now doesn't know

which size it's going to give to this

put in the size or initialize your array

like this and it is going to work in

this case we're going to have six

elements and and you see that a range

based for loop is going to come in handy

here because we don't really know the

size of this array if somebody comes and

adds another element let's say 23

the size is going to change and if we

hard to code the size in our full loop

the code is going to break but a range

based for loop is going to use whatever

size this already has so we're going to

try and build this we're going to build

and the world is going to go through if

we run rooster we're going to get the

elements we have 10 12 15 11 18 17 23 if

we add a new element this is going to

you see that we don't need to modify the

put in the new size and this is really

cool i like this about range based for

loops we're going to build again

run the rooster and this is going to

give us exactly the data we have in the

array so this is one way you can do

things another thing we saw is that you

so let's do an example here for example

we're going to grab this thing and uh

put an array declared down here we're

going to copy that and use that here and

we're going to make this cost

let's give it a name let's say

birds for example for example we want to

lines of birds or whatever this is just

an example to show you that you can't

modify this array so if you try to do

and index 2 for example and you want to

the compiler is going to complain you

see that visual studio code is

expiration must be a modifiable value so

it is saying that the array stores const

elements so you can't modify elements of

this array okay so this is something you

can do if you don't want people to be

able to modify data in your array and

the last thing i'm going to show you is

that you can do operations on the data

so let's bring up our scores array again

so we're going to go up and copy it

because the code is using there so let's

put in our own scores array

it's going to be pretty fast and we're

going to say that it is an array with

this angle brackets we're going to

initialize this let's put in a bunch of

values and what we can do is sum these

things up we're going to store our

results in the sum variable and we're

going to loop around with a ranged based

for loop because we don't really know

the size of this array it can change any

time with however many elements and a

range based for loop is really cool in

that we don't have to keep track of the

so we're going to go in here

so for example for the first time sum is

going to be 0 because that's what we

initialize it with we're going to get

into this loop here the first element is

going to be 2 we're going to add that to

0 and get 2 we're going to add a 5 we're

going to get a 7 we're going to keep

adding this element and at the end sum

is going to contain the sum of all these

elements in the array here and this is

one cool way you can sum up the elements

in your array so if we run this we're

going to get the sun printed out let's

do that pretty quick we're going to run

this has to build with gcc and we have

what is happening here it's going to say

redeclaration of scores where did we

declare scores before let's go up and

make sure it is not declared somewhere

so we want to comment this out

come back to our code so that we can see

and we're going to build again with gcc

and now the world is going through we're

sum is 37 and if you sum these things up

i'm sure you get 37. this is really all

we set out to do in this lecture i hope

you have a better idea of how you can

declare your arrays put data in read

data out of those arrays make them const

or even do all kinds of operations on

them and this was really what this

we are going to stop here in this

lecture in the next one we're going to

see a cool way we can use to get the

and meet me there in this lecture we're

going to see a way we can query for the

at runtime if you remember in the last

lecture we had an example like this

showing how we can declare an array and

initialize it in a single statement like

but the problem we had with this is that

if we tried to print the array using a

for loop for example we would have to

use the size and the size of this array

may change if somebody decides to add

elements or remove elements then the

size is going to be irrelevant c plus

plus provides a way we can query for the

size of an array at runtime and we're

going to get the real size accounting

for the current number of elements that

we have in the array and for that we use

this is a function that comes with the c

plus plus standard library so you're

going to have it already if you have a

compliant compiler if you see here you

see that it was introduced in c plus 17

and it is a cool addition we can use it

to make our code easier to work with if

you look here we have a simple loop

which is going to print data out it is

going to loop starting from zero all the

way to the size of the array you see

that we use this to control when this

loop is going to end we then put in our

incrementation part and then we jump

into the body of the loop and print the

current element in the loop and if we do

things like this we're going to be able

to print all elements in the array

regardless of the number we initialize

it with okay so this is one way and it

was introduced in c plus plus 17. but

how did we do things before z plus plus

well we had to kind of do a hack to get

something like this we use the size of

operator we have seen a lot of times

if you do size of and passing the array

you're going to get the entire size of

the array so if we take that and divide

that with the size of a single element

in the array we're going to get the

number of elements of the array and this

is really what we are doing here we are

setting up a count variable and we are

taking the size of the array and

dividing that with the size of a single

element in the array and we are just

grabbing the first element because you

can really use any element here and once

we have this we can use this count to do

a loop like this and it is working

please remember that you don't have to

go through this craziness we're doing

here you don't even have to use std size

because you can use a ranged base for

loop and get access to the elements you

have in the array and it is going to

work pretty well now that you have an

idea about this let's head to visual

studio code and actually play with us

okay so here we are in our working

folder we are going to be working on

this project size of an array we're

going to grab our template project we're

going to copy the files and put them in

and we're going to open this up in

visual studio code let's do that it's

going to open up in visual studio code

clean it up a little bit and we are

going to declare an array if we want to

we need to know how many times we're

going to loop and print elements in here

so one thing you might want to do is to

say okay we have 10 elements in here so

i'm going to loop for 10 times you might

think this is going to work and it is

and build this with gcc like we usually

and run rooster we are going to get our

numbers this is what we have in the

but what if somebody comes and changes

the elements we have in here let's add

the moment we change this we will need

to come and change the size in here and

this loop here might be buried somewhere

deep in your project and it might not be

as easy as it is now to see that we also

need to change this this may be a really

big source of hard to debug problems so

what we really need is a way to get the

size of the array at runtime and be able

to dynamically query for that size and

use it in our program and that's exactly

what std size provides so we're going to

and we're going to put in a value let's

use a braced initializer so we're going

and we're going to pass the array we

and if we do this we're going to get

and we're going to be looping for this

number of times so we're going to test

for i is less than the count here

and now it doesn't matter how many

elements we have in here we're going to

get them at run time we need to only

update this initializer here so what we

and run rooster and we're going to get

the numbers here you see that we get all

the elements if we take out a few of

these elements let's take out a few of

these let's leave it up to seven or

let's build again and we are going to

clear and run rooster we're going to get

however many elements we have in there

and this is pretty cool again you might

ask how did we do things before c plus

plus 17 because std size was introduced

in c plus plus 17 let's say that here

before that we had to get the size of

the entire array and divide that with

the size of each element in the array

and we could use the size of operator to

do that so before we do any of that we

want to play with the size of method to

so what we're going to do is say sdd the

scores the entire array and we're going

to print that and we're going to say

you know one element let's say

scores and use the first element this is

the easiest thing we can find here but

you can use any element so we're going

to say size of here and we're going to

say scores and grab the first element

which is at index 0 and we're going to

print its size if we build and run this

and the world is good we can clear now

and run rooster you're going to see that

we're going to get size of scores is 32

the entire array the size of one element

is four because we are storing in

integers and i want you to see that 32

is four times eight because we have an

eight elements so it's going to give you

the combined size of all of the elements

that we have in here if you do size of

but if you do size of a single element

you're going to get the size of a single

element so c plus plus developers were

and see that we could use this

information and get the count of

elements inside so we can do something

and we're going to assign a value to

in our braced initializer so we're going

and we're going to divide that with size

of and i'm going to grab scores we can

really use any element in the array but

we're going to grab the one at index 0

and now we're going to get the count

stored in our account variable without

using std size and we can uncomment our

or the code to print the array and if we

run now it is going to work exactly the

same thing regardless of the amount of

elements you have in here let's put a

few numbers randomly and if we will then

run we are going to clear and run

rooster and we're going to get all the

you can really use any of these

techniques just choose what you feel

works better for you okay we are going

through all this trouble to set up an

iterator we're going to do the test

we're going to increment this is really

too much work to try and get data from a

collection like an array so what we can

do instead is comment out all this hard

and we can use a ranged based for loop

as we have seen before and it is

ridiculously easy and convenient to work

with so what you can do is say for

type deduction on whatever it is we have

stored in our array so we're going to

and we're going to print out the element

so let's do that we're going to print

stdcl and here we're going to say value

let's say value in the array and we're

i and this is going to print all the

elements and we can work with the values

inside if we want that but you see that

on the indexes so if you really need the

indexes you will need to go through

something like this and if you just need

the values in the array ranged based for

loops are going to be really cool let's

say range base for loop and if we boiled

and run this it's going to work pretty

so the world is going to go through

let's bring this up so that we have some

breathing room we're going to clear

and we're going to get our elements

printed out here and you see that it is

the exact same thing we have in scores

so this is really all we set out to do

in this lecture i just wanted you to be

facility that we have in the c plus plus

standard library if you don't want to

use it for any reason you can also go in

and do the division we did here to get

the count of elements in the array

and uh do your best to try and use

ranged basis for loops because they make

it easier and cleaner to get data from a

collection like we are doing here with

an array we are going to stop here in

this lecture and the next one we're

going to see how we can work with arrays

go ahead and finish up here and meet me

in this lecture we're going to work on

array of characters and show how special

you can declare an array of characters

just like any other array so here we

an array called message it stores

elements of type character the size is

five and we initialize it with a bunch

if we want to print it out we can look

like we loop through any other array in

this case we're going to be using a

ranged base for loop we say for auto c

we pass the message and then we're going

to be printing each character in the

message and if we do this we're going to

see hello printed out on the console we

can also modify elements in our array

for example we can say message1 and

and if we print out we should see hello

printed out on the console nothing

really special so far the cool thing you

can do with character arrays

is that you can print them to the

console directly without even doing the

loop you can do something like this you

can do sddc out you say whatever you

want to do in quotes here and you're

going to print the message but sometimes

this one to do what you expect because

only proper c strings can be printed on

the console and what makes up a proper c

string a proper c string has this thing

you see on the end here this backslash

is called a null termination string and

it is what is going to tell c plus plus

that we have hit the end of the string

and we are going to stop printing it if

we are printing with things like stdcl

so this is really important to be in

your strength if it's not there it may

work but sometimes it's also going to

print some garbage characters after this

because what tells sddc out that we have

reached the end of the string is this

backslash zero here if it's not there

it's going to keep printing until it

sees one and then you're going to

probably have some garbage characters

added to your string and that's not what

you want so to have your strengths

printed out correctly be sure to have in

this null termination character here and

if we print it out we're going to get it

and we're going to see the size printed

out properly if we do things like this

but it is possible to get to this auto

field for us if you look here we have a

character array called message2 inside

we have said that we need six elements

and we say hello so we have one two

three four five elements and the

elements we don't initialize properly is

going to be initialized with a zero

version of a character and that happens

to be the null terminator of the null

termination character so this is going

to print correctly and we're going to

backslash n appended to this for us by

the compiler but be sure you understand

the difference between this and this

here we have specified the size to be a

5 and we are putting in five elements so

we have no null character appended to

this string but here we have said that

we can put in six elements and we have

only put five and the compiler is going

to autofill then the null terminating

character these two things are different

and make sure you understand the

difference okay so now take a look at

what we have here we have a strand we

didn't specify the size and we just

initialize it with hello someone might

think ah this is also going to autofill

but it's not because the compiler is

going to deduce the size of this array

using what you initialize it with and

you didn't put in a null character so

it's not going to be accounted for

you're only going to have this here and

if you print this out you may get

garbage characters appended to your

string here so be careful but it is

possible to do literal c strings and

only say hello like this in quotes and

you're going to get the null terminating

character appended to your string here

so if we print this this is going to

pretty nicely and this is the

recommended way to initialize your

character arrays if you want to put in

string data like this you have to use

double quotes and the cool thing about

this is that you can even put in

spaces between words like this it is

going to work this really looks like how

you would like to type text and store

that in your character arrays and we're

going to be using this a lot in the

course again i want to bring to your

attention that character arrays are

in that you can directly print them on

like we are doing here you see this is a

character array and we are saying stdc

out message for you can't do this with

other arrays and this is really all i

had to share about character arrays so

what we're going to do next is head to

visual studio code and play with us okay

here we are in our working directory the

current project is arrays of characters

we're going to grab our template project

and we're going to copy the files

and we are going to open our folder

we're going to open the main cpp file

and we're going to get rid of what we

don't need here let's put in some

startup code so that we can start

playing with this without typing this

too much so we're going to declare an

array of characters it's going to be

called message the size is going to be

five and we're going to fill it with

characters like this so if we do this we

might want to print it like we print any

other array we're going to use loops and

a range base for loop so we take a toast

in message and we're going to print out

each character notice that we're not

adding std endl here because we want the

characters printed close to each other

so that we can read this easily and

after this we will need to go to the

next line so that the next thing we

print doesn't disturb us so we're going

to say sddc out std endl and if we do

this we're going to see hello printed

out on the console but we had to do too

much work to print something simple

like hello but let's do this we are

so we're going to bring up our terminal

and we're going to build with gcc let's

the world is going to go through and

and run rooster you're going to see that

it's going to say message is hello and

this is what we expect and this is

really how you would declare an array of

characters and initialize it with

whatever it is you want to initialize it

with but you notice that it's really not

convenient to put data in here if you

want to store a message for example for

someone you don't want to do this thing

you see here it's really ugly it's

convenient and nobody would definitely

use your program if you required your

users to type things like this so we

need to change this and we will but

before we get there let's also see that

we can change characters in our array so

if you look here this e here is at index

two so what we can say is a message and

uh we're going to target the element on

let's use that so this is index zero the

h and the e is at index one let's make

sure we get this straight and we're

in quotes remember characters are

surrounded by single quotes like this

once we do this and we try to print the

technique here we're going to copy the

code and we're going to paste it down

and if we do this we're going to see the

message printed out here to be hello

and the second message is going to be

because we changed the second element

to an a it's no longer an e so that's

what we expect we're going to run the

test to build with gcc and we're going

to bring this up and clear and we're

going to run rooster you see that we

have message hello and message hello and

we are able to print things successfully

this is really cool but we are doing too

much work really to print something on

the console and there should be an

easier way to do this and there is so

what we're going to do is comment this

out because we don't want noise output

in the console when we try to do

so what we're going to do is comment out

all we've done so far we're going to

leave in our message here and we're

going to try and print it directly on

the console so we can say sddcl

and we're going to print out the message

and take a moment and look at this

and try to compile this it is going to

go through it is going to compile

supports printing character arrays like

in most times this is not going to do

what you expect let's try and run this

we're lucky to get something that really

it's pretty hello and you see that we

have a bunch of other things and the

reason is what we have discussed in

these slides for character arrays like

this to be printed out properly

on the console they need to be null

terminated in other words they need to

have the null character which is a

backslash zero appended to the string

for sddc out to know that it has reached

the end of the string so this is what

makes your character strings legal

now you see that we are getting a

compiler error because we have overflown

the size of the array i think that's the

message too many initializer values and

this is exactly what we have done

now we can try and change this guy to a

six to say that we have six elements in

this wiggly line should go away and if

we're going to build with gcc

let's bring this up a little bit and

and you see that now we have hello

printed out correctly if we turn this

and take out the null terminator

we're going to try and build again and

we're going to clear and run rooster

you're going to see that we get the

garbage back so for your strings to be

printed out correctly they need to be

now terminated that's why it is not safe

when your character array is not now

terminated i really want you to

understand this so in c plus plus we

have a proper name for these strings

that are null terminated a null

terminated string is called the c string

because these things come from the c

programming language okay and we're

going to see a few ways we can set up c

strings now and the first one is to say

car we can call this message one

and it's going to be an array of

characters and we're going to initialize

this with hello let's copy this because

i don't want to type all these

things here so let's copy this

and initialize this properly notice that

we didn't specify the size so the

compiler is going to get the size from

however many elements we put in here and

we're going to put in our null

terminator here and if we print this

this is going to work and we are going

to comment this out and i'm going to say

that this will give you garbage okay if

we come down here we're going to see

that we have a car array it is called

message1 and we have initialized it with

data we have hello and we have a null

terminator here and the compiler is

going to deduce the size so this is

going to be a proper c string and we

let's try and weld this the board is

going to go through if we clear and run

rooster we're going to get our message

here and this is one way we can set up a

proper c string the second way is to

actually not putting the null terminator

but let the compiler add that in for you

and the way we can do that we can say

car message to and we're going to say

this array is of size 6. let's say that

and a fix how we end things here we're

and end this with a semicolon now what

is going to happen is the compiler is

going to see that this array is of size

6 but we are putting in five elements so

the remaining slots are going to be auto

filled and it is going to be using

null terminators to autofill this then

if we try to print the size here we're

because the null terminator is added in

by the compiler let's try and print the

sizes here actually so that you can see

these things so we're going to say size

and we're going to say that size of

message one and we're going to put in a

new line character and this should be

what we expect so what we're going to do

and i put that down here because we're

going to be doing the same thing for

message to so we're going to say message

and i say size of message to and do

signs of message too so what we're going

to see is a message 1 and message 2

printing out and we expect to see a size

of 6 because both of these guys have six

elements inside so we're going to run

and this is exactly what we expect

message one is hello the size is six

message two is hello and the size is six

and these are a few ways you can declare

your character arrays and initialize

them with proper data that is going to

print correctly with stdc out make sure

you don't do something like we did here

by printing message here because it is

not null terminated this is going to

give you a lot of problems again i want

that message three here is not a proper

c string because the compiler is going

to deduce however many elements we have

in here and this thing is going to be of

and we're not going to have a null

terminator and if we print it out we're

going to get some garbage so let's try

and copy this so that we are consistent

what we've done above here and if we

we are going to compile successfully but

we may get weird things if we print out

message three like we do here and you're

going to see that the size is five

because we only have five elements in

here so let's clear and run rooster and

we have hello for message one we have

hello for message two but for message

three we have things we don't expect

because it's going to keep printing and

it's going to go overbound and it's

going to stop when it hits the first

like what we have in here okay so this

is not safe don't do it make sure your

it if you intend to print them with sddc

out like this okay so working with

character arrays like this to print

messages and do all kinds of crazy

things is nice but it really isn't

you wouldn't expect your users to type

characters like this by surrounding them

with single quotes this is really ugly

and it is painful to do if you want to

do some productive work so c plus plus

allows you to use what we call string

literals and we're going to see an

down below we're going to say string

literals and uh what we can do is car

message for it's going to be an array as

with a string that is surrounded by

double quotes and what this is going to

is you know take these things break it

into characters and store this in this

array here and make sure you properly

now terminate this string here so if we

print the size of message four we're not

going to get five we're going to get six

because c plus plus is going to see

these double quotes and know that we

intend for these things to be properly

null terminated and it's going to add a

null terminator so let's try and print

this out so that we really are sure and

we're going to weld this with gcc as we

the world is going to go through let's

go up and clear and we're going to run

and you see that message 4 is hello

so this is one way we have to do things

and do all kinds of crazy things and

it's really cool and if we try to build

this we're going to get the proper

message printed out you see the world is

good if we clear and run rooster we're

going to see hello world how are you

doing and this is really cool so from

now on if we need to store a string in

our program this is how we're going to

do it because this is much more

civilized and it is how you would really

like to type characters in your program

i have said that character arrays are

really special because you can directly

print them out with stdc out like this i

want to prove this so we're going to try

and declare another array so we're going

and we're going to make this an array

and we're going to initialize with one

two three four five this is going to do

and we're going to put our closing

semicolon and we're going to try and

print this out i'm going to say std

let's try and compile this and see what

we get it is not actually going to give

us a compiler error but it's not going

to print what we expect and let's put a

message here so that we know that it is

this thing we are seeing here so we're

going to say numbers and we're going to

and if a run rooster look out for the

output that says numbers here so let's

run rooster it's not a one two three

four five it's something we don't really

and we will get to understand what is

in the next chapter for now note that

you can't directly print arrays other

than those of characters if you try to

do that you're going to get weird

numbers printed out and we're going to

the next chapter so let's say that here

okay this is really all we set out to do

in this lecture i hope you found it

interesting character arrays have a few

things you need to be careful about and

we try to cover those in this lecture we

are going to stop here in this lecture

and the next one we're going to try and

go ahead and finish up here and meet me

there in this lecture we're going to

look at what could happen if you try to

manipulate data out of the bounds of

your array we have seen that when you

allocate space for an array the computer

is going to give you a bunch of memory

locations you can use to store your data

and it's going to be of the size that

you have specified or that is deduced by

the compiler so here is an example of an

array that is going to store seven

elements and we have green slots for

these elements and these are the

locations we are allowed to manipulate

in our c plus plus program if we try to

go overbound for example if we try to

modify something before our array or

it might be a memory location that is

owned by another program it might be a

memory location that is even being used

by the operating system so bad things

can really happen if you try to use data

that is outside the bounds of your array

let's try to look at a simple example

here here we have an array called

numbers we have 10 slots inside so we

are only allowed to modify the memory

locations for these 10 numbers and if we

try to access something outside the

bounds of this array something might

happen but some people say that c plus

plus is really funny because it should

be stopping you from doing something

like this but c plus plus allows you to

do this if you look at code here we have

an array we have 10 elements n so the

valid indexes we can really use are from

0 to 9. but if we try and access

something at index 12 the code is going

to compile and if we run it we're going

to get something printed out but that's

something this is going to give you

garbage data or you might be even trying

to read some restricted memory and your

program is going to terminate

immediately and we're going to say that

it has crashed if you try to write over

bounce the compiler is also going to

allow it but you don't own the memory so

other programs might come and change

that memory location and if you try to

read from it again you're not going to

get what you expect another thing that

could happen is that you try and modify

data that is owned by other programs and

you might imagine how bad that really is

so the message here is don't go over

your array balance and you're going to

be playing in the safe zone let's head

over to visual studio code and play with

us a little bit here we are in our

working directory the current project is

array balance we're going to grab the

and we're going to open this up in

visual studio code we are going to

declare an array and try to read beyond

the legal bounds of our array so let's

try and bring up a terminal here and we

are going to build this with gcc the

world is going to go through you're not

going to get a compiler error but if we

run this we can really get anything and

you see we have a number we don't really

know what it means and this means that

out of the legal bounds of your array

allows you to do this and the reason

they do this is because they expect you

the developer to know what you're doing

when you try manipulating things like

ray and now you know this and be careful

when you are working with arrays like

this so don't go overbound that's the

message we may also try to modify data

beyond balance so let's go down and put

in the code to modify thanks and i have

put a clear message here as a comment to

let you know that this is really

something you should be very very

careful about so we're going to try and

change that number to 1000 and we're

going to try and print it out and see

what we get but this memory location at

is not something we own so other

programs might come and write to this

location and if we try to read from it

again we might not get what we put in

here even worse this memory location

might be owned by other programs and if

they read they're going to get what they

didn't put in they're going to get what

you put in and this is something bad we

might try and really go crazy with us

let's put in a really huge number and

this is a good way to learn by the way

and let's try and print what we have in

there and we're going to say

and that's what we're going to say here

and we're going to build again the world

is going to go through you see that we

are doing something really crazy our

array has 10 elements but we are trying

1 million memory locations away and uh

this is really crazy and c plus plus

so let's clear and run did we world

let's make sure we have world so let's

and run rooster our program is crashing

because we are trying to access

that isn't really ours and you see it

okay for example if we have something

printed out after this let's say std

and then so that you can see it is

this statement here is not going to

print because once we hit this location

we're going to try and modify this and

the program is not going to be able to

do that it's going to crash the

operating system is going to notice that

we are trying to do something crazy and

it's going to say this program is really

crazy it doesn't know what it's doing i

am going to kill it and it is going to

stop that's basically what is happening

here so let's weld again with gcc

and run rooster you see that it's going

to try and do this it's going to try and

put a value in here the program is going

to end here and this is really bad

because memory locations you have

allocated for before here are not

properly released and returned to the

operating system and this is something

don't go overbound make sure you are

working within the legal boundaries of

your array welcome to this new chapter

and we are going to be talking about

pointers pointers are one of the

important topics in c plus plus and they

allow you to do some of the things very

conveniently and we're going to be

learning about all those tricky things

you can do with them in this chapter but

now i want you to have a basic

understanding of what a pointer really

so far we have been working with

variables like this we set up a variable

in our c plus plus code we get to a

point where we put a value inside that

variable and we could use it for example

we could print it out on stdc out or we

could even store a value or assign

another value to the variable we've been

doing that quite a lot but there is a

point we haven't really been talking

about those variables have an address in

memory and here for example you see that

is stored at location one zero zero

eight of course this is a simple example

but i hope it drives the point home all

the variables you use in your code have

some kind of address in memory

and we can grab that address and store

that in a special kind of variable which

is really a pointer so we can say that a

is a special kind of variable

that stores addresses of other variables

make sure you really understand this

here we have p var so it is a pointer

its type is end pointer and we denote

pointer using this star symbol after our

type if you see something like this

you're going to know that this type is a

pointer to end its name is going to be p

and its value is going to be the address

of another variable you see it is

storing 1 0 0 8 which happens to be the

address of our var here in memory

pointers and variables we've been

talking about can work hand in hand and

we're going to be seeing how this is

done in the next few lectures in the

chapter but the basic idea is really the

same here you see that we have a pointer

to it but you can have a pointer ready

to anything in your code you can have a

pointer to car you can have a pointer to

double you can have a pointer to float

even pointers to custom types we haven't

really talked about now but we will

learn about them later in the course

again a pointer is a special type of

variable in your c plus program that is

going to store addresses to other

variables that's what it really is and

we're going to start and see how you can

declare initialize and use them in your

code starting in the next lecture

go ahead and finish up here and meet me

in this lecture we're going to see how

we can declare and use pointers in our c

plus plus code in the last lecture we

say that a pointer is a special kind of

that can store addresses to other

variables in our c plus plus code and we

have seen a slide like this to drive the

point home now we're going to see how we

can actually use pointers in our code

here is a simple example of how you can

declare a pointer variable in your c

plus plus code you say ent you put a

to mean that this variable is not a

regular variable like we have seen

before it is a special kind of variable

addresses to other variables and here i

have to say that you have to be really

careful and only store addresses to

in your pointers for example this is a

pointer to end it can only store an

address of a variable of type and for

other types if you try and put in their

addresses in here you're going to get a

compiler error down here you see we have

another example and it's called p

fractional number because it's a double

and you see that our pointers here are

initialized using braced initializers

and this is going to initialize the

pointers with a special address that

really denotes that these pointers are

not pointing to anything yet okay you

can also say that explicitly and put now

ptr inside and this is going to mean

that these pointers are not pointing

anywhere you can't really use the values

at the addresses where they point this

is the message here don't use pointers

that contain null pointer all pointers

on a given system are going to have the

same size for example if you have a

pointer to end and the pointer to double

they are going to be the same size

because they really store the same thing

they store addresses to variables and

addresses to different variables even if

they happen to be of the same type on

the same system are of the same size

that's why all the pointers you're going

to use in your code are going to have

the same size and this is something you

should keep in mind and here is a simple

example to really play with that we have

a size of it printed out we have a size

of our pointers printed out and we're

going to compare these things when we

get to visual studio code in a minute

and you're going to see that all

pointers are of the same size a question

i get from many people is if the

really matters and i have to break it to

you it doesn't but i prefer to put it on

the left some people prefer to put it on

the right but definitely don't put it in

the middle i've never seen anybody do

this but it's going to work it's going

to be legal c plus plus code another

thing i see people do which is really

confusing is to declare your pointers on

the same line and do a comma like this

this is really going to be confusing and

now i want you to guess and see what is

happening here is either it var a

pointer or it's a regular end i want you

to keep this in mind i'm not going to

tell you we're going to try this out

actually in visual studio code and we're

going to figure this out together but

now i want you to try and think about it

we're going to leave this question

unanswered and we're going to answer it

in a little while but for now

don't really do this because it's

confusing and it's going to make your

code less readable if you have to do

something like this make sure you just

put them on different lines and it's not

going to be confusing for example if you

look down here you're going to know that

p number seven is a pointer other

interval is a regular end and there is

no room for confusion this time use code

like this and don't put things on the

same line like we have on top here okay

now we have seen that we can declare and

initialize pointers with null pointer

now is the time to see how we can put

actual data in those pointer variables

here we have a variable which is called

into var it is of type and and its value

we can also set up another pointer

underscore int and we can initialize it

with the address of another variable and

here is a new operator we haven't seen

before this ampersand variable here

really means the address of this ant

variable that's what we mean here so

we're going to initialize this p end

variable with the address of enter

variable and this is how we do it

if we go down here we print antivirus

we're going to get the value printed

down if we print the pointer directly

we're going to get the address of this

little guy printed out on the console

and we're going to see it okay so this

is how you can store things in your

pointer variables and what you have to

store and has to be an address of

down here you see we have another

variable called into r1 inside we have a

65 and if you go down here you see that

we are storing something else

in our point of variable here we had in

the address of into var now we are

putting in the address of into var1

using an assignment operator and this is

something you can definitely do it's

legal c plus plus it's going to work if

we print it out we're going to get a

different address printed out this is

how you can store values in your pointer

variables again you can't cross a sign

before different pointer types here we

have an eight pointer which is called

pn1 and we have a double variable it's

called double var we can't take the

address of double var and store that in

pnt1 this is going to be a compiler

error the variables whose addresses you

store in payment 1 have to be of type

and again the basic idea is that a

pointer is really a special kind of

variable that is going to store

addresses to other variables and if your

the variables whose addresses you can

store in this pointer to end can only be

ends if you try and put in doubles

you're going to be in trouble you're

going to get a compiler error and it's

not going to work now we're going to

head over to visual studio code and

actually play with these things here we

are in our working directory the current

chapter is pointers the current lecture

is declaring and using pointers we're

going to grab our template files and put

so put them in our project here and

we're going to open this in visual

studio code the first thing we're going

and initialize pointers and we're going

to use a pointer to end as a first

example we're going to set up an inch

pointer and we say in store we're going

to give it a name we're going to call

this p number and you can leave it like

this uninitialized but it is really

advised to always initialize your

pointers so we're going to do that with

a brist initializer which is going to do

that for us this is going to implicitly

initialize it with zero equivalent of

pointers and that happens to be null

pointer so we'll initialize okay so this

is what we're going to initialize with

and this is how you should do things you

can also do a pointer to double why not

let's do double pointer and we're going

to say fractional number pointer to

fractional number and we can also

initialize this with null pointer

once you do this the program is going to

be legal if we try to world at with gcc

like we always do the build is going to

be good but we don't really have any

if we run this program we are just

getting started we will get to see

things later for now just understand

that p number is a variable we have in

our code this variable can only store

addresses to other variables that happen

to be of type and if you try and store

in an address of a variable which is of

type double for example or flute you're

going to get a compiler error you

shouldn't do that the same for p

fractional number it can only store

addresses to other variables which

happen to be of type double keep this in

explicitly initialize with no pointer so

we can say end pointer and say p number

one why not and we're going to

ptr like this and this is going to work

one why not and say now pqr this is

going to work this is something you can

do you're going to see that if we

compile this the compiler is going to be

happy with this the world is good okay

now you know how you can declare and

initialize your pointers now we want to

that pointers to different variables are

on whatever system you are working on

it's not consistent across operating

systems or riffing systems but it is

guaranteed to be of the same size on the

i am going to go down and put in a piece

of code that is going to show us all

these things on the console and i am

going to click on this file icon here

some breathing room so that we can see

the entire thing here if you look here

we are printing the size of ant we know

that this is going to be a four

size of double this is going to be an

eight on our system here but we don't

know what the size of a double pointer

is or the size of an end pointer and

we're going to see that in a minute here

you see that we are also using the

pointer variables immediately this is

something you can do you see that visual

studio code is not complaining and we

can go on top here and boulder with gcc

the world is going to be good now we can

open up a terminal and actually run this

program here we're going to clear if we

our directory here so you see that we

and we can run this and it's going to

sizeofant is four size of double is

this is expected but pointer types are

of size 8 on my system they occupy 8

bytes in memory so it doesn't matter the

type we are pointing to a pointer to it

is always going to be 8 bytes in memory

this is something you should really know

and keep in your mind another thing we

have said that i want to play with right

is the location of the star symbol some

people say you should put it on the left

some people say you should put it to the

right i don't really think any of these

dense matters i prefer to put it to the

left but if you put it to the right it's

also possible it's going to work you see

that even if you put it in the middle

here which is really crazy the compiler

is going to take this we can run the

task to build this to make sure the

compiler is really happy and you see

that there's no problem the compiler is

going to accept this and we are going to

build successfully if you put your

declaration on a single line like this

what is other ant var going to be is it

going to be a regular end variable is it

going to be a pointer to end

we don't really know now and i don't

want to tell you we're going to find out

together so what we're going to do we're

going to print the size of these things

i am going to go down here and put in

the code and come back in a minute here

is our code typed out and we're going to

see the size of these things what we're

going to do is run the task to build

with gcc as we always do let's clear

and you see size of p number five is

because it's a pointer size of either

end is four and the same applies to the

so from this we can tell that other

interval and other ant versus x are not

pointers they are regular integers and

this can be really confusing so to avoid

this confusion i would advise not to

your thanks when you have pointers

inside like this because that's going to

be really confusing what you can do is

put them on separate lines and do

something like this so here it is very

clear that p number seven is a pointer

other eight var seven is a regular it

variable and there is no room for

confusion with this way of doing that so

make sure you put things on separate

lines like this and you're going to be

fine now what i want you to see is that

we can actually store data in all

pointers i mean valid data that is not

null pointer in this case we're going to

set up a variable a regular end variable

it's going to store a 43 inside and

we're going to set up another pointer

and initialize that with the address of

this it variable and this is going to

work properly what we can do now

is print the interval we're going to

print it out if we try to print the

pointer we're going to get the address

of this into var in memory and this is

something you need to see with your eyes

this is the first time we are printing

out an address that is stored in a

pointer and we're going to see that on

the console here what i am going to do

before we build and run this i am going

to comment out everything we've done

before because our console is now

so let's come and comment out everything

and let's go down again now if we print

we're going to see these two statements

and that's going to be easier to follow

on the console here the build is good so

and the var is 43 and its address in

memory is this number here it is in

hexadecimal so this is the address in

memory and we can print that out and see

what it is okay so this is really cool

but we can also change what is stored in

our pointer here for example we can set

up another variable call it into our one

and uh change pnt which is a pointer to

contain the address of this new variable

and we can do that now if we print

payment we're going to see that it

contains a different address and we can

so let's build with gcc again

we're going to go down and clear and run

rooster and we're going to see that now

we have a different address the one we

had ended in d e4 now we end in de0

these are different addresses and we are

storing different things in our pointer

this is really cool you can do something

like this and the next thing we want to

see now is that we can't cross a sign

between pointers of different types and

what i mean here is that for example if

we have two variables here one is a

pointer to end it is initialized with no

pointer and we have another variable

which is a double var it's going to be

and we can't do something like payment

equals address of double bar you can't

do something like this if you do it

you're going to get a compiler error and

you see that we have squiggly lines

in visual studio code this is a good

indication that something might be wrong

if we open the problems tab we're going

to say a value of double pointer cannot

be assigned to an entity of type 8

pointer so this is not something you can

do if you do this you're going to get a

compiler error be aware of this visual

studio code has warned us enough but we

a clear compiler error by building this

with gcc and we're going to get

basically the same thing you can't

cross-assign between pointers of

different types we are trying to assign

into a pointer to enter and this is not

going to work so let's comment this out

because we don't want this compiler

error now you know this and before we

close this lecture i want to mention

what is called the referencing and that

is the act of reading something

through a pointer so if we have an

address in a pointer we can go through

that address and actually read the value

contained in that address and we can do

something like this so if we have for

example an end pointer let's call it p

and two do we have a variable like this

so let's say we initialize this with

nodepointer and we have an end

variable and this is a 56 for example

and we do something like we do say

pnt2 we're going to make it contain the

address of int data this is something

you know you can do now now we want to

go through pm to 2 to read what is

contained in interdata because pn 2

contains the address of our integer here

so what we can do we can do stdc out and

say value and the syntax we use in c

plus plus is like this we say store and

we say our pointer variable we're going

to say pnt2 and now if we run we're

going to get the value here printed out

okay now if we try to build we're going

to build fine let's try with gcc

a previous run are cleared out

you see the bullet is good we can now

and we're going to see that value is 56

reading the value stored in the address

pointed to by our pointer here and this

is the syntax used and this is called

the referencing a pointer we are

basically reading something stored in

the address of a pointer this is what we

mean here this is really all we set out

to do in this lecture the lecture turned

out to be lengthy but we had a lot of

ground to cover and now i hope you have

a good grasp on how to declare

initialize and use your pointers to do

we are going to stop here in this

lecture in the next one we're going to

learn a little more about pointer to

character types because they are also

go ahead and finish up here and meet me

there in this lecture we're going to

explore pointer to characters

and you can declare a pointer to a

character just like this we have car

and we say p carvar to give it a

variable name we initialize this with a

null pointer and after that we set up a

character variable and it is called

corvar and we store in an a in uppercase

a after that we take the address of car

of r and assign that to our pointer

variable this is how we store data in a

pointer and we can go through this

pointer to access data in this character

variable if we do something like this

we're going to print a down here we

declare another variable we store in a c

assign the address of this new character

variable to our pointer variable and if

we print this again we're going to get a

c printed out this is really what we

have done in the last lecture we are

just extending that to character

pointers but with character pointers you

can do something really special what you

can do that is special you can

initialize that with a string literal

something like hello world which is

wrapped in quotes like this when you do

something like this the string here is

going to be expanded into a character

array and the first character of our

array is going to be pointed to by p

message here this is what we mean i

realize i might be throwing a lot of

things at you right now i am mixing up

arrays and pointers but they have a

really strong relationship and we're

going to learn about that in detail in a

think of it like this this hello world

string is going to be turned into a

character array and the p message is

going to point to the first character

in this array here this is what is going

to happen and this is going to give us

the flexibility of treating our

strengths as character pointers and this

is going to come in handy at many

one thing i should tell you though is

that some compilers will refuse to

compile this code for example visual

studio 19 that i have installed on my

computer right now is going to refuse to

compile this code and the reason is the

compiler is going to expand this

a character array of const car

and here what we are using to point to

that is not a cost car pointer

so this pointer here can be used to try

and modify data into an array of cost

cars and that's going to be disastrous

because if you try to modify that

that's going to fail and that's not

going to be good so some compilers are

going to try and protect you from this

and force you to use pointers that are

qualified with cost to really mean that

they are closed car pointers and to get

the code to work we will have to do that

and i will show you how we do that in

visual studio code but i have to tell

you this in case you just want to jump

ahead and try this code out if you get a

compiler error that's going to be the

reason now that we have our strength

stored in memory we can really print it

out like this if you print p message

you're going to get this ring printed

out but i want to give you a question

what do you think we will get if we

i told you that the compiler is going to

expand this hello world string into an

array of characters or to be specific an

and p message is going to be pointing to

so if we dereference p message we're

going to get that character printed out

in this case we will get an h and that's

what is going to happen here but

character pointers are special in that

if you print them out directory the

compiler is going to do its magic and

make it possible to print out the entire

string that is stored in p message here

that's how character pointers are

special and you really need to be aware

of this because this is going to come in

handy many times just to emphasize that

this is going to be expanded into an

array of constant characters if we try

something inside p message here for

example we try to change the h into a b

we can try to do that because p message

is pointing to the first character so we

can try to dereference and assign a new

value and if we do that we're going to

get a compiler arrow or even worse we

might get a crash at run time so this is

something you shouldn't really do and

your p message here as the cost card

pointer and that's going to prevent you

from doing things like this which may

turn out to be very bad but most

compilers are going to even prevent you

from compiling this thing in modern

times for example if you are using a

of visual studio you're going to get a

compiler error but i don't believe gcc

is going to give us a compiler error so

we will have to try this out and see how

it behaves but the message is if you

have to do something like this make sure

you use the cost car pointer and you're

going to be playing on the safe side

okay now i think you know enough about

character pointers what if we want our

users to be able to change this string

and make it be something else for

example change the first character here

into a b well in that case don't use

character pointers use regular arrays

like we have seen before so you can set

up an array like this it's going to be a

character array and you can initialize

it with the string literal and this is

going to allow you to modify things

inside so if we do something like this

we will get the message printed out and

the message is going to be tailored

because we changed the edge to be

a t and this is going to work so this is

something you really need to be aware of

but character pointers are very helpful

in many cases and in most cases you just

want to store the string and print it

out you're not interested in changing it

so that's why this is going to come in

handy in a lot of occasions now that you

know this we're going to head over to

visual studio code and actually try this

out okay here we are in our working

folder the current project is pointer to

car that's what we are exploring here so

we're going to grab our template files

and put them in place and we are going

to open this thing into visual studio

code and we're going to jump into here

and set up our first const car pointer

let's do a car pointer to see how this

thing behaves we're going to call this

message and we're going to initialize

this with our trusty message here hello

world okay once you do something like

this your string is going to be referred

by message let's try and compile this

and see that gcc is happy we can compile

and uh it's going to tell us we can't

really do that and this is really good

for base converting a string to constant

card pointer so what we are doing really

is making an array of const characters

and refer to it as a car pointer and

this is not going to work this is a good

thing so you can't really do this and

and let's try and see if visual studio

can actually do this we're going to

build with msvc in this case let's do

read to rooster before we do that we can

right click to add and say delete

make sure it is selected and hit delete

move to recycle bin in this case

now we're going to clear here let's

and we're going to build with gcc

we're going to choose the msvc compiler

if you're trying to build this

with errors and the error is going to be

basically the same thing this line here

won't work what we can do is make this

cost and make it super clear

that message here is going to point to

if we try to build again i think we're

going to be good now so let's try and do

we're going to build with msvc this time

and world finished successfully

now this is really cool and we can print

and we're going to say message

let's go back to gcc because that's my

favorite compiler and you see that the

compiler from visual studio is going to

clutter our folder here with a lot of

we don't want that what i'm going to do

i'm going to select all this collector

here and remove that and i'm going to

hit delete with the right click

we're going to go back to gcc and use it

the build is going to go through because

we qualified our character pointer with

cost here and everything is going to be

you know what is happening here because

this kind of problems can be really hard

to solve okay now that we have this we

can try and change something inside but

the compiler is not going to allow it so

if we try and do something like this is

not going to work because message is a

and we can't go through this pointer to

modify something so we're going to get a

compiler arrow this is something you

should know but we can add the reference

this pointer and print something that is

inside and i want you to guess again and

see that you can come up with what is

going to be printed if with the

reference message and print out when we

run this program if we have this thing

printed out here again we are the

and printing whatever result we get from

that remember that this string literal

is going to be turned into an array of

const cars and the first element of that

array is going to be pointed to

by this message car pointer here so if

we dereference this thing we should get

the h here printed out that's what i

the bolt is going to be good let's clear

see that message is h this is exactly

what we expect here now that we have

what if we really want this thing here

to work what if we wanted to allow our

this message thing and modify what is

stored inside because sometimes that's

useful okay we wanted to allow our users

to modify this trend if you want to do

that you can use row character arrays

and the way we do that we can say car

message one and we can make it an array

and initialize that with hello world and

once we do this we can go through the

angle bracket syntax and modify the

first character or whatever character we

really want to modify in this string

here in this case we are going to target

the first so we're going to say message

1 and we're going to grab the index 0

because that's going to be the first

character here and we're going to assign

b like we just said and if we print this

out say message one and uh put that out

we're going to see what comes out if we

run this program we're going to build

the world is good so we're good here

if we're on we're going to get below

printed down and we have successfully

changed this thing here so if you don't

want to allow modifications to your

strength use this thing here if you want

to allow modification to your strength

use this syntax here and this is really

in this lecture in this lecture we're

going to revisit our idea of a c plus

memory map we have seen that the c plus

plus development workflow really goes

like this we have a program typed out in

our ide we pass that through the

compiler and we get a binary executable

which is a binary representation of the

code we have in our c plus plus program

you can then run that program on an

operating system for example here i am

on windows if i double click on my dot

exe file for example our applications

rooster.exe you've seen me run this a

if we double click this program is going

to be loaded in our computer memory and

by memory i mean random access memory

the memory that is going to be actively

running things when they happen in your

computer is different from the hard

storage that can also be called memory

and this can throw off a lot of

beginners we are talking about ram here

when we mean memory random access memory

to be exact if you double click on your

program or open it on the terminal like

we've been doing the program is going to

be loaded in memory and it's going to be

stored in a special section of memory

called program area and so far we have

been thinking that our program is really

loaded in real memory on our computer

but that's not the case it is an idea of

the memory that the program thinks it

has but it's not the real thing and i am

going to explain but before we explain

let me elaborate on the reason why this

is done if we have many programs and

each program is going to use real memory

on our computer we could quickly run out

of memory because there are many

programs you might even have hundreds or

thousands of programs running on your

computer you may never have enough

memory to run them all if real memory

create what is called virtual memory and

it is a trick that pulls your program

into thinking it is the only program

running on your operating systems and it

owns or the address space or all the

memory on your computer that's what your

program thanks and the view that your

program has of that memory is called a

memory map each program is abstracted

into what we call a process you can

that we have been welding as a process

on the system and each process has

access to the memory range between 0 and

2 to the power of n where n is the

number of bits that your operating

system supports for example i am on a

64-bit operating system so the range for

my memory is going to be between 0 and 2

to the power of 64. and that's a lot of

memory my program is going to think that

it owns all that all and it can never

run out it's going to do whatever it

wants if you are on a 32-bit system

that's going to be between 0 and 2 to

the power of 32 and that's going to be

your virtual memory the amount of memory

that your program fans that it owns and

it happens to be the entirety of your

ram that you have on your system each

program basically thinks that it owns

the entire memory and it can do whatever

it wants okay so we have the rio memory

which is random access memory and we

have virtual memory which is going to be

between 0 and 2 to the power of n okay

so now we're going to update on the idea

of the program execution model because

now we know more we know about virtual

memory here is our c plus program it's

going to go through the compiler and we

are going to generate a binary file

which is going to be a representation of

how things are going to be laid out in

it is going to go through a section of

the cpu called memory management unit or

mmu for short so that mmu is going to be

basically transforming between the

memory map of each process and the radio

memory layout that we have in ram what

the memory management unit does is

representation we have in the memory map

and the real thing we have in ram the

entire program is not loaded in real

only parts of the program that are

really going to be used soon unloaded in

memory and this is going to make

effective use of the memory parts that

are not likely to be used are going to

be discarded from memory and stored on

the hard drive instead and this is

really cool please note that the real

way these things are done is really

complicated but it is buried down into

the logic of the cpu and whatever you

don't really need to worry about this as

a super plus programmer but there are a

few things you need to know as we are

about to see in this lecture so memory

management unit helps out in mapping

the memory map you have in your program

basically the idea that your program has

of memory and the real thing

that we have in memory okay here is a

slide that is going to drive this home

we have a few programs with their own

separate memory maps we have program one

if we execute them they are going to go

through the memory management unit and

the memory management unit is going to

assign them sections on the real

ram that we have in our computer and

they are going to be using that section

on the real random access memory that we

have on our computer the thing is your

program is going to really think it owns

but it's not just going to be using a

part of it and the memory management

unit is going to be transforming between

the idea that your program has and the

real memory that we have on our computer

and the memory map is a standard format

that is defined by the operating system

this is why for example you can't take

an executable that was set up on windows

and directly run it on linux this is an

operating system thing the memory map or

the structure of your program is defined

by the operating system that is going to

be running that program so all program

written for an operating system must

conform to the memory map that is

defined by that operating system so all

programs on windows if you had a way to

go in and look at the memory map they

are going to be pretty similar so we

have been talking about the memory map

well here is a slide that is going to

try and clear that out so we're going to

have a bunch of memory locations from 0

all the way to 2 to the power of m

and the memory map is really divided

into a lot of parts for example we have

the text section we have the data

section we have the heap stack and

and this is one view you can have on

this there are a few different versions

of this slide that you're going to see

on the internet but what is really

important is stack and hip for our

purposes here stack is what is going to

store our local variables thank the a

that we have here in main bc thanks we

had inside functions those things are

stored inside the stack section of our

besides the stack we also have the hip

which is going to be the location where

we get additional memory we can use to

make things better for our program we

also have the text section which is

going to load the actual binary of our

program so that the cpu can execute it

but we're not going to worry too much

about this section in this course

because it is out of scope for

what we are trying to do here we are

going to focus on stack and hip because

hip is actually going to be very

important from the next lecture when we

start talking about dynamic memory hip

is going to be additional memory that

you can use in your program if you run

out of stack memory and we're going to

see a few other reasons why you might

want to use this as we progress in this

chapter so our memory map is going to

have a lot of parts but the parts that

we really care about in this course are

stack and heap this is really all we set

out to do in this lecture i hope you

have a better idea of the memory map and

how this really works we introduced

another view that you can have on how

your c plus plus program is executed and

i hope you have a better idea of the

memory system and we are going to start

and see how you can work with dynamic

memory allocation which is going to

go ahead and finish up here and meet me

in this lecture we're going to start and

learn about dynamic memory allocation

and this is a technique we can use to

start using hip storage that we have in

the memory map of our c plus plus

program we can use that to get

additional memory we can use and do

stuff if stack memory isn't enough for

our purposes this is how we have been

using pointers so far for example we

have a variable we set up a pointer and

we store the address of the variable n

so we can go ahead and use this pointer

to manipulate the variable or do all

kinds of crazy things if you go down

here we have a pointer p number one

and we have a number one variable and we

can store the address of number one into

this pointer it's really the same thing

like we have on top here but the pointer

is not initialized at declaration here

and you have to make sure you put

invalid data and one thing i haven't

really stressed enough is that it is

really bad to try and use a pointer that

is not initialized for example here we

have p number two which is a pointer it

is not initialized it contains junk

and we try and write into it okay so try

to think about what we really are doing

here this is a pointer that we have set

up we haven't really initialized that so

it's going to contain whatever address

is possible it can contain an address

that is used by another program it may

contain an address that is being used by

the operating system it's not your

address to mess with and here we are

actually trying to mess with that by

storing in a 55 so this is going to

cause the crash possibly or even

corrupt data that is being used by other

people so don't do this another thing is

to try and use a pointer that is

initialized to know for example here we

have a pointer p number three and it is

braced initialized this is going to

initialize it to null pointer but we are

trying and storing in a value here so

this is also going to be bad it's not

granted what you're going to get

actually c plus doesn't give you any

guarantees this is called undefined

behavior so you're going to get a crash

and don't do it as a good practice the

first thing you should do is initialize

before you use them you can initialize

them with no pointer and make sure that

modifying valid addresses into those

pointers if you don't know what is in a

pointer don't use that pointer because

bad things can happen okay rule number

one don't try to use a pointer that you

rule number two don't try to work with a

pointer that is pointing to no ptr

that's going to give you bad things you

don't want to really deal with okay so

far we have been using memory that lives

on the stack section of our memory map

we were using variables that we have

declared in the main function we were

using the variables that we have

declared inside some functions and

that's all stuff that live on the stack

now we want to see how we can use the

hip okay let's take a closer look at our

memory map we have the stack we have the

and the differences between these two

the stack memory is finite so you don't

have infinite memory but the same is

true for the heap but hip is additional

memory that you can use if you don't

want to run out of stock memory for a

stack memory the developer isn't in full

control of the memory lifetime so if you

declare something on the stack for

example if you say int var1 and you

initialize that to 23 you don't control

when that variable is wiped out of

memory the variable is going to be

killed when the scope in which it was

and you developer don't really say when

the variable dies and sometimes you

when your variable dies so this is a

limitation we have with the stack memory

okay so for stack memory lifetime is

controlled by the scope mechanism we

just say that for heap the developer is

in full control of when the variable

comes to life and when the variable dies

and this is a benefit you might have

with heap storage and you might want to

use this and we're going to see how we

can use that in the next few lectures

okay so make sure you understand the

difference between stack and hip here if

you look at the example here we have a

variable which is called locoscope var

it is stored within this block delimited

by the curly braces and the variable is

going to come to life when this

statement is executed but it is going to

when we hit the closing curly brace here

so the lifetime of this variable is

controlled by the scope mechanism but it

is possible to use dynamic memory or use

memory on the heap and we're going to

see a syntax you can use to do that the

first thing we want to do it to set up

employer that is going to be pointing to

that heap allocated memory the way you

do that you set up a pointer here we

have p number four we initialize it with

but what we do to allocate memory is the

second statement here we say p number

the moment this statement is going to be

executed the operating system is going

to allocate a piece of memory on the

heap the memory is going to be large

enough to accommodate for an integer so

it's going to be four bytes long

and it is your memory now your program

can use it to do whatever it wants and

no other program on the system can use

this piece of memory so it is going to

be yours until you explicitly return

this piece of memory to the system and

we're going to see how you can do that

in a minute once this memory is yours

you can use it you see here we already

referencing the memory and the story

again is 77 and if we're trying to print

this 77 we're going to get it printed

out okay this is how you can use dynamic

things are not being stored on the stack

things are being stored on the heap i

really hope you understand this because

it is very important okay so here is our

view of stack and heap so if you use new

to allocate for memory stuff are going

to be stored in this hip section here of

your memory map here is another example

to try and understand the lifetime of

our variables docovar again is limited

to this scope it is going to come into

life when this statement here is

executed and it is going to die when we

run out of this scope here so if you try

executing code out of this scope locovar

is no longer going to be available you

can't use it but that's not the case for

locro ptr var because this is a pointer

and if you go out of this scope the

memory is still going to be yours if you

have a way you can access it and use it

you're going to be able to use it and it

is going to be yours until you decide to

return it to the operating system so we

have been talking about returning the

how do we do it well you use the delete

keyword in c plus plus here we have our

memory which is allocated using new and

so the operating system is going to give

us a new piece of memory it is going to

be four bytes because we're going to

store in an integer and we are going to

be pointing to that memory through p

number four here we can use this memory

however we want through the referencing

and do all kinds of crazy things and

when we are done with this memory we are

going to say delete p number four and

this statement is going to return the

memory to the operating system the

memory is no longer going to be hours

after this statement and a good thing to

do after you release your memory is to

no ptr so that other people know that

you don't really have any valid data in

that memory because if you try to use a

memory section bad things are going to

happen that's not going to be your

memory we're going to fall into the same

uninitialized piece of memory don't do

that so whenever you release memory also

reset it to no ptr to play it safe we

can also initialize our pointers with

dynamic memory when we declare them and

this is how you can do it we say p

number five and we initialize that with

new and this is going to give us a new

piece of memory on the heap and it is

going to be pointed to by p number five

we get the same thing here but uh here

we are just pointing in new values and p

number seven the memory locations on the

heap are going to be containing 22 and

23 for p number six and p number seven

and here we have a few examples of how

we can print the contents of these

and after you are done using your hip

memory you're going to release it using

the delete keyword and you are going to

reset that to no ptr to really play it

safe this is how you should use dynamic

memory allocated on the heap another

thing you should know is that it is

really bad to call delete twice on a

pointer so here we have a memory

location that we allocate on the heap we

we are trying to use it here in sddc

and if we delete it for the first time

that's going to be cool it is going to

be returned to the system but if you try

to delete it for the second time you're

going to get a crash don't do this this

is really bad okay now that we have a

slightly clearer idea about pointers and

dynamic memory allocation i think it is

time we went to visual studio code and

actually played with a few of these

concepts here we are in our working

directory the current project is dynamic

memory allocation we're going to grab

our template files and we're going to

put them in place dynamic memory

allocation let's do that and we're going

to open this in visual studio code the

first thing we're going to do is review

how we have been using players so far

we have been using them like this we had

a variable stored somewhere on the stack

again this is the stack memory that we

stored addresses of some variables you

know pointers something like this and we

could go through the pointer to

manipulate that memory location for

we can print the address of that memory

we can even the reference and print the

by doing something like we do here and

we are not printing here so let's say

that and say p number we can do

something like this and we have been

doing this quite a lot so far we can

also have a piece of memory that is

uninitialized and we store the address

of some variable in that piece of memory

and we can do the same thing for example

if we print p number one we're going to

get the value 12 printed out here and we

could run this so let's try and do that

we're going to bring up a terminal first

and close this pane so that we have some

breathing room and we are going to build

we're going to build successfully going

to clear and run rooster and we're going

to see that we have these things printed

out here the variable we have in here is

22 so we're going to get that if we

if we print pointer we're going to get

the address printed out we can also go

through the address of operator to print

the address of this variable here but we

can also print our value through the

referencing our pointer and we can get

access to it here down here we have a

pointer that is not initialized so it

will contain a junk address that you

shouldn't really use but we're not going

to do that because we're going to store

in the address of number one here and we

can manipulate the value here through

the pointer using the the reference

operator here and if we print this p

number one we're going to get 12 printed

out this is pretty cool okay so this is

how we have been using pointers so far

let's comment this out because we're

going to see some other things okay

before we really look at how dynamic

memory works we are going to show you a

few bad things you need to be aware of

so let's put in a piece of code for us

and here we are saying that writing into

uninitialized memory is really bad so

uninitialized and we are trying and

directly right into it through the

reference and this is going to be bad

visual studio code is not complaining it

thinks that we know what we are doing

here and it's not going to warn us but

this pointer could really be pointing

anywhere including operating system

specific memory and here you may be

modify things that your operating system

is going to need so clearly the

operating system is not going to be

happy about this and the bad things can

so now we have this memory location

we're going to try and write into it and

we're going to see what happens if we

run this program for now let's try and

take this little section here and

and we want to see what happens on the

program here the code here that we might

let's try and build it with gcc we're

going to run the task to do that

the build is going to be good you see

that we don't even get a compiler error

and if we're trying to run rooster you

see that the program is going to try and

run you know the operating system is

going to say this guy doesn't know what

they are doing and i am going to close

them you see that it's not even

this statement here let's go on top here

and put in an sddc out statement so that

where this program is failing

okay so this is what we have we have a

few statements other than and we want to

see if we actually get to run these two

where the program is actually failing

we are going to build it again with gcc

and run rooster you see that it's going

to say writing in a 55 but this

statement here is going to fail because

we are trying to ride into memory that

is not ours and the operating system is

going to stop us so our program is

crashing and it is terminating before it

even runs the things that are down here

hopefully you can see how bad this is

you have designed your program to do

things but it is going to stop

without having done any of the other

things that you have designed below so

this is really bad and another bad thing

you might have allocated some dynamic

memory beforehand and your program is

going to end before it even releases

that memory properly and returns that to

the operating system so this is bad you

don't want crashes in your programs and

don't ever try and use and reference

memory that you haven't initialized this

is one bad thing we're going to comment

this out i hope you really know how bad

this is and we're going to go down again

and uncomment what we have done here

and uh it's going to be another bad

thing because we are trying to write

initialized to null pqr okay here we

have a pointer this is called p number

three and it is initialized with no ptr

you can think of ptr as an address that

says i don't have any valid thing in me

don't use me that's what no ptr is

initialized to ptr but we are trying to

store something in here and you can

imagine how bad this is this is memory

that isn't really valid the memory

itself is saying i don't contain

anything valid don't try to use me and

if you try to use it bad things are

going to happen so if we try and compile

this program it is going to compile the

compiler is not going to stop us to do

and these are some things you need to be

aware of in c plus plus but if we try to

run it you're going to see that we are

also going to get a crash again let's

try and put a statement in front of this

failing line and uh below this line i

and both of the programs so that we can

see which std statements run and which

dot after our program crashes so we're

going to clear the world is good and run

rooster you're going to see it's going

to say what it's doing it's going to try

and fail and the operating system is

going to kill this program because it is

crazy it is doing what it shouldn't

really be doing so this is something bad

don't do it be aware of this thing okay

we're going to comment this out and

actually look at how we can dynamically

allocate memory from the heap and we're

going to put in a piece of code to play

it's not really complicated we have a

pointer we initialize it with no pointer

to say that this pointer doesn't point

to anywhere valid don't use it and we

calling new and when we do this the

operating system is going to give us a

new piece of memory on the heap

this piece of memory is going to have

the size enough to contain it so it's

going to be four bytes in memory and we

are going to be pointing to that piece

of memory using p number four here this

is what we are trying to say here the

moment we do this we own this piece of

memory and nobody else on the operating

system can use it so that's something

you should know once you have it you can

manipulate it through the pointer here

so here we can go through the the

reference operator and store in 77 and

if we print it out we're going to get

that printed out here okay this is

really cool this is the first time we

use hip memory and i am excited about

showing you this thanks we're going to

try and build this program and the build

is going to be good and we are going to

and if we run rooster we should see a 77

i'm going to get our 77 but this 77 is

stored on the heap now it is not stored

on the stack and this is really

really cool we can control when this

variable comes alive by allocating

memory on the heap and we exactly

control when this variable dies

if we want and we're going to see how we

can kill this variable from memory but

for now just take a moment and

appreciate how good it is to be able to

allocate stuff on the heap it is really

cool now that you have used the memory

it is really time to return it to the

system because we have no more use for

it the way you release memory to the

system is to call the delete keyword

and say the pointer pointing to the

memory that you are trying to release to

the system so we're going to say p

number four here let's bring this down a

little bit so that you can see the

entire story so we have a pointer here

and it is pointing to dynamically

allocated memory from the heap this

large because it stores an integer

we have it dynamically allocated we use

it here and it is time to return it to

the operating system okay i hope this is

clear the moment you call the delete

now the memory is going to be containing

some junk and you don't want to really

use that anymore if you try to use it

it's not your memory you're going to run

into trouble so for example after we

delete this memory if we try to use it

i'm going to show you here i think i can

let's say p number four and um storing

something notice that we are using the

the reference operator and let's try and

so let's build this with gcc as we

always do it is going to world compiler

is not going to stop you from doing

writing into memory that you have

released to the system but we're going

to see what happens so run rooster and

it is going to say done writing but you

see that the program has really crashed

because here we are trying to write into

memory that we don't really own and this

is bad don't do this so the moment you

delete the memory or the moment you

return the memory to the operating

system it is good practice to reset that

memory to no ptr so we're going to say p

make sure it contains no ptor

at least when we do this other people

have a chance to check and see that

that's valid memory before they use it

that's the use of resetting your memory

here so this is something you should do

again the flow to use dynamic memory is

really simple you set up a pointer that

is going to point to your memory

allocate the memory from the heap using

the new operator you're going to specify

the type you want to allocate memory for

the operating system is going to give

you that memory and you're going to be

pointing to that memory with your

pointer you are going to manipulate that

memory using your pointer and doing all

kinds of crazy things and after you are

done with that memory you're going to

release it to the operating system and

please remember to reset your pointers

after you have deleted them like this

that's going to make your life a whole

lot easier and other developers are

going to thank you for doing this

when they get to use your code because

your code is going to be much safer to

work with okay let's comment this out

and show you another example of what

cool things you can do with dynamic heap

memory we're going to go down and put in

a piece of code and show you that you

dynamically initialize your pointers at

declaration this is something you can do

the first one is not initialized so it's

going to contain junk volume p number

five if we try to print it we're going

to get some junk address print it out p

number six we're going to dereference it

and print the value inside so we're

going to see that and we can do the same

thing for p number six and p number

seven after we are done using the

pointers we are going to release the

memory here and notice that we are

resetting the pointers to no pointer to

say that they don't really contain

anything useful don't use them make sure

you have something valid and before you

use them this is the meaning here if

you're trying to run the program you can

guess what we're going to see so try and

guess and we're going to build we're

going to weld successfully going to

clear not clear and we're going to run

rooster and we're going to see that p

number five contains some junk address

okay and if we try to dereference that

we're going to get a junk value this is

really not useful don't use this value

because you didn't put this value in in

the first place you're going to see that

p number 6 is going to point to some

other address but we're going to have a

valid value inside because we have put

that n at initialization here the same

is true for p number seven it's going to

point to some address and we're going to

have 23 and because we put in our 23.

this is how you really use these

pointers another thing i want you to

know is that even if we have called

delete and reset these pointers they are

still available for use in our program

so if we want we can reuse these

pointers so for example p number five we

and use it to allocate new memory so we

okay so we can go down here and use that

this is going to be valid c plus plus

okay take a moment and look at it it is

and the visual studio code is going to

take this because it is valid c plus

plus code the memory has been returned

to the operating system and the pointer

has been reset to no ptr but we can

reuse this end pointer to allocate new

memory so we are allocating new memory

on the heap the memory is going to be

going to contain an integer and we are

to point to that new memory so this

pointer is being reused it was pointing

the memory that we allocated here which

was uninitialized and we are using that

memory location on the hip i really want

you to understand these things because

many beginners get them wrong and it is

hard to correct these things in your

mind once you have a wrong idea about

them in the first place so make sure you

understand this so if we print this

we're going to get the 81 printed out

we have allocated new memory we have to

remember to release it again so we have

p number five and we need to reset it to

once we do this we're going to be

playing it safe let's try and run and

see that we see the at1 printed out

we're going to build with gcc the world

and we are going to clear and run

rooster and you see that we see our 81

and we don't have any crazy crash for

example to prove that we don't have a

crash we can say that our program is

if the program has actually reached the

end before it dies we're going to build

and run rooster and you're going to see

that the program is ending well

the other thing i want you to see is

that it is really bad to call delete

twice on a pointer again it is really

bad to call delete twice on a pointer

don't do that okay we're going to see an

so we're going to allocate new memory

using p number five why not so we're

going to say p number five and we're

going to say new and going to allocate

new memory on the heap and we're going

to store in a 99 in that memory we can

print out the 99 so we're going to say

and after we are done using this memory

we are a good c plus plus citizen so

okay this is good it is going to work if

we will then run we're going to get what

we expect we should get a 99 printed out

last in our program before it ends and

we see that printed out here program

ending well this is really cool

but if we try to call delete twice

and try to boil you see that the

compiler is not going to stop us because

so this is something you need to be

aware of in c plus plus if we run this

you're going to see ah the program is

not going to end well the c plus plus

runtime or the operating system is going

to get here and see uh this guy is

trying to release memory twice and i

don't do that this is a bad program i am

going to kill it and it is going to be

killed the bad thing again is that

anything you have in your program after

these lines is not going to run because

the operating system is going to kill

your program at this line here so if you

had memory allocated that you planned to

release later on in your program your

memory is not going to be released

because those statements to release the

memory will never be run this is where

the program is going to be killed the

operating system is going to see that

you are a rug program and it is going to

kill the program so don't delete your

memory twice this is something you

should really watch out for and you

might think uh-huh i know this why would

i call delete twice in a single line

here well you may not do it like this

but your program might have multiple

where you have pointers pointing to the

same memory and if you try to delete

that memory twice you're going to get

this error and this is really good so

watch out for these kinds of things and

we're going to see different ways you

use to really make sure you are doing

things right in c plus plus this is

really all we set out to do in this

lecture giving you first-hand practice

on how to do dynamic memory allocation i

hope you found this useful we are going

to stop here in this lecture and the

next one we're going to learn about

go ahead and finish up here and we'd be

there in this lecture we're going to

focus on dangling pointers and show you

how they can be bad a dangling pointer

is a pointer that is pointing to a valid

address and we have seen a few examples

of this already but in this lecture

we're going to focus on that and show

you common solutions we can apply to

these problems here and download

pointers are really bad they are going

to lead you programs to undefined

behavior and we have seen that that can

many times there are three kinds of

dangling pointers we're going to look at

in this lecture the first one is a

pointer that is not initialized the

second one is a deleted pointer and the

third case may come if you have multiple

pointers pointing to the same memory

location and let's look at these cases

one by one here we have an example of a

pointer that is not properly initialized

this is p number five it is a pointer to

and it is not initialized it doesn't

really point anywhere and it is going to

contain junk address if we try to

dereference it we're going to get bad

things to happen because we don't really

know which address is stored in there

and putting something in there might

lead to a crash so this is something you

need to watch out for the second kind of

dangling pointer that can really lead

you to bad places is a deleted pointer

here is a pointer p number one it is

initialized with dynamic memory and we

can use it for example here we are

dereferencing the pointer and printing

the value inside and deleting the

pointer after we delete the pointer

don't really use it before you properly

initialize it with some kind of memory

if we try to do that this is going to be

undefined behavior and your program

might crash so make sure you don't do

something like this another case is if

you have multiple pointers pointing to

the same address and here is a simple

example to drive the point home we have

pointer three which is pointing to

dynamic memory here we are using new ant

in our braced initializer and we are

putting value 83 in that pointer

and here we set up another pointer p

number four and we initialize that with

another pointer and if we print these

things out we're going to get that they

contain the same address and they

contain the same value we're going to

and try to use p number four later we're

going to get problems because this

memory has been deleted by p number

but p number four is still pointing to

that and if it tries to use that it's

going to be deleted memory basically and

we're going to get undefined behavior so

be sure you know these problems and try

to avoid them in your programs okay

these are problems but how do we solve

them well there are a few solutions one

is to always initialize your pointers

the moment you declare a pointer make

sure it is initialized if you don't know

what you can initialize that pointer

with put in null pointer first and then

you're going to put in an address later

when you have a clear idea of which

address you can store in the second

solution is to reset your pointers to

now ptr after you delete the memory

that's the second thing you should do

every time you call delete that's going

to give other developers or even

yourself a chance to check and see if

contains a valid address before you do

that and for multiple pointers pointing

to the same address you have to choose

and make one pointer the master of the

and all pointers are basically going to

be slaves which can't release the memory

but they can read and do something with

that memory that they don't have the

task of releasing that memory and here

is how you can apply solution one for

example we have pointer number five and

we're going to brace initialize it this

null pointer the other thing you can do

is initialize the pointer with dynamic

memory like we are doing here with p

number six and this is going to put in

the value and we are going to be playing

now if your pointers are initialized

developers have a chance to check your

pointers against no ptr to see that they

contain something valid before they use

it and if they see that it contains no

ptr they are not going to try and use it

and this is going to be very safe for

the second problem with deleted pointers

we are going to reset our pointers after

we call delete for example here we have

pin number seven initialized with

dynamic memory and 82 is stored in we

can print it out all do things with it

when we delete the memory we're going to

reset it to null p2r so that other

developers or even ourselves can check

this memory against no ptr and if it's

different from no ptr we can use it if

it's equal to no ptr we're going to

leave it alone and do something else

this is going to be very safe if you

have multiple pointers pointing to the

same address like we have here then

you're going to have to decide which

pointer is the master pointer and other

all the other pointers are going to

check against the master pointer and see

that it contains valid memory because

the master pointer has the task of

deleting this memory let's go through

this and see how this could work in

so p number five is our master pointer

we are setting p number five and

initializing it with p number eight we

are creating things using p number eight

we can either use p number eight or pin

urban eye this is going to work but

before we use the memory location we're

going to check against the master

pointer if the master pointer contains

no ptr we're not going to use this

memory if the master pointer doesn't

contain now ptr we're going to use this

memory here okay if you go down you see

that the master pointer is going to be

releasing the memory and if we try to

use that memory after it was deleted

we're going to see that it contains now

ptr and we're not going to be using it

this is something cool and it is really

easy to implement this safety guidelines

in your programs now that you know about

this we're going to go to visual studio

code and show you this in action okay

here we are in our working directory the

current project is dangling pointers so

we're going to grab our template files

pretty quick and put that in our project

and we're going to open this in visual

studio code we are going to look at the

first case of a dangling pointer and

this is a pointer that is not

initialized properly like p number here

if we try to reference it we're going to

so let's see that and let's go down and

say that program is ending well just to

know that we didn't get a crash because

a crash is basically going to terminate

your program on the offending line

that's what it's going to do so if the

works well and ends well we're going to

gcc to build this program and let's open

run it we're going to clear the world

and we're going to run rooster

you see that the program didn't end well

it crashed and it crashed because we are

uninitialized memory when the operating

system is going to try and run this

thing it's going to see ah this guy is

trying to modify memory that doesn't

really belong to him it is a road

program i am going to kill it and it is

going to be terminated on this line here

you should avoid these kinds of

situations so don't do this we are going

to comment this out and show you another

offending event we can do in our program

and that is using a deleted pointer if

you do that you're going to get

something bad in your programs

so here we have a small example we have

a pointer to end we initialize this with

a dynamic piece of memory and we're

and we can print this out this is going

we delete the memory down here and we

try to use it after we have deleted the

memory so the operating system is not

going to be happy about this because

once the memory is deleted it is no

longer our memory so we have no business

the referencing pointer one and trying

to use that here and we're going to get

and this is something you should avoid

so let's try and build this and show you

this in action we are going to clear

and you're going to see that program is

ending well but in some cases it might

crash and hopefully this shows you the

that these things might put you into

sometimes your program is going to seem

working fine but sometimes when this

memory that we are pointing to in p

number one here is being used to do

something really important by the

operating system you are going to get a

crash so you're not guaranteed to get

the same behavior every time you run

your program some of you might be saying

aha the program is working here daniel

why are you making this such a big deal

well it is a big deal because you are

not guaranteed to get the same results

every time you run this program so be

sure you really avoid these kinds of

situations let's try and clear and run

the program again hopefully we're going

to see it crash but we're not okay so

let's clear and rebuild again

and see that we have a better luck that

and run rooster it is going to end well

but you notice that we are trying to use

a piece of memory that has already been

deleted and this is bad don't do this

make sure you don't do something like

this we're going to comment this out

again and show you another offending

thing we can do with our programs and

bad things might happen if you try to

have multiple pointers played into the

same address and that's what we have

here we have p number three and p number

four here p number three is allocating

new space and it is pointing to it we

have an 83 inside and a p number four is

initialized with p number three we can

do that so these two pointers are

basically pointing to the same memory

let's run this and show you that

we're going to comment out this delete

statement here and run the program first

to really prove that they are pointing

to the same addresses and they contain

the same values let's build and run

we're going to use gcc for that

and we're going to clear and run rooster

p number three the address is this and

it contains an 83 p number four contains

so let's see what happens if we try to

and using p number four later to try and

read stuff this is what we are doing

and we're going to see if the program

we're going to build again the world is

going to be good let's bring this up and

and you're going to see that the program

but we are using a deleted piece of

memory here and anything can really

happen okay so you might get garbage you

might have really any piece of junk

inside or you might get a crush in some

extreme cases so this is really bad

don't do it don't try to use a piece of

memory that you have already deleted

through a pointer and these are problems

you might run into in your programs if

you try to use dynamic memory allocation

let's look at how we can solve them

make sure you put a little ptr in a

pointer if you don't know what that

pointer is actually stored at okay let's

go down and look at solution one

solution one is to initialize your

pointer to no pointer every time if you

don't have a value you can put in use

null ptr that's what we are using here

implicitly but we can explicitly put

that end because it is good and before

you use a pointer you have to check and

see if it doesn't contain null pointer

this is how we do it if pointer six is

different from null pointer we're going

to use it if it is equal to no pointer

we're not going to use it and we're

going to be playing on the safe side and

you're going to see that the program is

going to end well here if we have a null

invalid address okay and that the user

is going to know that they are trying to

do something really bad so let's try and

so let's go and store a null pointer in

p number six to really try this out and

show you that we're going to get this

warning if we're trying to use it

and we're going to build with gcc and

we're going to clear and run rooster

you're going to see that invalid address

and the program is going to end well

and if we try to put this statement

somewhere where we're not shaking

no pointer we are going to get a crash

so let's comment this out so that it's

clear what it is we are running here

so if we run this we're going to get a

crash we have seen that but let's show

and really highlight that we are solving

the problem here if we run rooster the

program is going to crash because we are

memory but if we try and check against

no ptr like we are doing here let's do

that we're going to be playing on the

safe side because it's going to tell us

invalid address and we're not going to

get a crush and the program is going to

end well this is really cool so let's

try and do that again we're going to

the world is going to be good we can

clear and run rooster and the program is

going to end well okay so if we have a

value inside we're going to get that so

let's put that n and say new ant and put

in an 87 for example it doesn't really

so we're going to build again the work

is going to be good and we can run

rooster and you see that we are getting

a value here if we are not storing no

ptlr in p number six and you can do the

same checks against p number five but i

think this is really enough so this is

one way you can avoid dangling pointers

the next thing we're going to look at is

if we are using a deleted pointer and

again the solution is to set a pointer

after we delete it here we have p number

seven it has 82 inside we are using it

here and printing stuff out we're going

to delete it after we are done using it

the first thing we do is to reset it to

no ptr when we do that other people or

even ourselves have a chance to check it

against no ptr and we're going to know

that it doesn't contain anything

for our program and if we do something

we're not going to run into all these

and our program is going to have

across different runs and this is really

cool so we're going to run this we're

going to get things printed out and the

program is going to end well because

right now we are checking against no ptr

we can even be explicit in showing the

warning here we can say invalid memory

access and if you run this program

you're going to really know this so

let's finish this up and we're going to

bolt and the bulk is going to be good if

we run this and run rooster we're going

to know that we are doing any valid

memory access after we have deleted the

pointer and this is going to save you

from possible crashes that you might

experience if you don't do this so this

is a second solution you might want to

and i'm going to comment it out and show

you how you can get away from the

multiple pointers pointing to the same

address we are going to go down and put

in the code it is what you have seen in

the slides and it is really nothing new

so we have pointer eight and pointer

nine here and p number eight here is

p number nine is initialized with

whatever we have in p number eight so

they are going to be pointing to the

same addresses here but we have made p

number eight the master pointer so it is

the only pointer that is going to be

able to delete this memory location even

if we have multiple pointers pointing to

okay so every time we want to use this

memory we have the option to check

against the master pointer and see that

we have some valid data inside if it is

no pointer we're not going to use that

and we're going to be playing on the

safe side this is really what we are

doing here if we run this we're going to

see that the program is going to end

the world is going to be good and if we

run rooster we're going to see that we

get things printed out we're going to go

through p number eight we're going to

print stuff we're going to go through p

number nine we're going to print stuff

and if we try to use the pointer

memory has been deleted we're going to

get a clear warning that we are trying

to do something really bad and this is

really what you should aim for in your c

plus plus programs that use dynamic

memory allocation and pointers

this is really all we set out to do in

this lecture i hope you know how you can

avoid these problems with dangling

pointers we are going to stop here in

this lecture the next lecture we're

fails to give you the memory that you

want to allocate on the heap and that's

possible go ahead and finish up here

and meet me there in this lecture we're

going to explore what happens when new

fails in the last lecture we saw that we

could use the new operator to allocate

for new memory on the heap and use that

to do stuff and in most cases the new

operator is going to succeed but in some

rare cases it is going to fail and when

you don't do anything about that failure

your program is just going to crash and

you might want to do something about

that i have to say that it is very rare

for new to fail in practice so you're

going to see a lot of code out there

that just uses the new operator it

checking if the operation actually

failed or succeeded so this is a very

rare case but if you need to handle it

we're going to see how you can do that

in this lecture here is a simple example

that is going to try and force the new

in the first segment here we are using

the new operator but we are using a

syntax that is going to try and allocate

a lot of integers in one go you see that

it is an array but we haven't really

seen how we can use an array like this

so just think of this code as a piece of

code that is going to allocate a lot of

integers in one go and we're going to

i have to say that this may give you an

error on some compilers saying that you

are exceeding the array size if that's

the case no problem we're going to find

another way to get this new operator to

fail we are going to put a thing like

this in a loop and we're going to loop a

lot of times enough to exhaust the heap

that is allocated to our program here

and when that happens you're going to

see that the program is going to crash

and it is bad so new can fail and if you

need to play on the server side you're

handle that problem and we have two ways

we can handle this problem we can go

through the exception mechanism this is

a built-in way we have in c plus plus to

check for arrows and handle them we can

also use the std no throw setting

in our new operator and force it not to

throw an exception and it's going to

give us no pointer if the allocation

fails i know this might sound cryptic

right now but we're going to see an

example shortly and you're going to

understand this let's look at how we can

use the exception mechanism the

exception mechanism is there in c plus

plus to let you handle problems when

they arise and the way you use that you

wrap code that is potentially going to

and try and catch blocks you see here

inside the loop we are saying try

and inside the tri blocks we have the

code that could fail we have our new

and in the catch block you see we have a

catch block here we're going to

and we have a way of catching the

problem and if you look at this thing we

have in this parenthesis after catch we

have an ex variable and we can ask it

leading to this exception happening in

our code you can think of this like this

i realize we haven't really talked about

exceptions we are going to talk about

them later in the course when we have

enough tools to really understand what

think of them as a tool to handle

when the new operator fails and you're

not going to crash your program your

program will keep running it will go

through the end but the new operation

that you wanted to do here will fail and

you will be able to catch that and this

is a good thing if you don't want to use

exceptions you can use the std no throw

and this is a new version of the new

operator you can use to tell the c plus

plus system to not throw an exception

when the operation fails it is just

going to return no pointer and you can

check for that and know that memory

allocation actually failed this is what

we're going to talk about in this

lecture i hope you have an idea about

this we're going to head over to visual

studio code and actually try this in

action okay here we are in our working

directory the current project is when

we are going to grab our template files

like we always do and we're going to put

them in place so when new fails that's

the lecture so we're going to do that

and open this in visual studio code

pretty quick and we are going to try and

allocate a large piece of memory in one

go so the way you do that we can do say

let's call this data it really doesn't

matter and we're going to say new and

and we're going to say that we want a

let's try and do that and we're going to

we know when we are ending this program

properly so let's try and compile this

we're going to bring up the terminal and

we are going to weld with gcc as we

always do and the build is going to be

good let's try and increase this number

and push it to a really big number and

have made visual studio code mad here

array is too large so they can't really

a really large array in here okay so

let's bring this down a little bit

and if we're trying to compile the

bullet is going to be good and if we run

rooster you see that the program

is going to not end well okay so this is

really a case where new fails we can't

on the heap storage that is allocated to

this program here remember when we

revisited the memory map idea we saw

that each program is going to have its

own memory map the memory map is going

to have a lot of sections inside we have

the stack we have the heap our hip is

not infinite so we can run out and we

just ran out with this allocation that

we did here and our program is going to

terminate immediately you see that it is

if this is not working for whatever

compiler you are using we can go and do

this through a loop so what we can do we

comment this out and we can really loop

many many times enough to exhaust the

memory that is allocated for this

in the memory map in the hip section

that's what i mean and if we do this at

some point the program is going to fail

and we're going to get the same problem

we're going to build with gcc

and we are going to clear and run

rooster and we're going to see it's

going to loop loop loop and it's going

the failure in a minute and we need to

find a way to solve this problem we have

seen that we have two options let's

and uh look at those solutions here the

first option is to go through the

exception mechanism we can also use the

std no throw option we're going to try

the exception mechanism first and uh

is wrap possibly offending code in try

and catch blocks and we're going to say

try here and put a block and we're going

catch and we're going to say std

exception and we're going to put an

ampersand symbol here just use this like

this and we're going to get a chance to

really explain these things when we have

enough tools to understand this for now

think of this as if i have code that is

like the new operator here i am going to

and if something goes wrong we're going

to get the error in the catch block this

is the way we do these things here so

for example i can take my loop here

and i know that this line of code could

so i am going to wrap that inside try

and catch blocks so i am going to grab

let's do that and align this a little

and we are going to take the potentially

in the try block and when the operator

something goes wrong and we're going to

catch the problem in the catch block

this is what we mean here again we don't

have enough tools to understand why we

are doing this thing here what is the

meaning of this ampersand symbol we're

going to learn about that later in the

course but for now we want to put

together something good enough for this

program not to crash like it was doing

right here okay we're going to catch the

arrow and say something went wrong

and we're going to print out what

actually went wrong we're going to say

a function called what on this

let's hide this pen here because we want

to see clearly what is happening here

this is how you can prevent your program

from crashing and it is going to end

well because now we have handled the

problem and that we haven't caused a

like we were doing down here now we're

going to try and build this code let's

bring it up a little bit so that it is

and we're going to weld with gcc the

bolt is going to be good and we're going

to clear and run rooster and it is going

to do its thing it's going to keep

and it's going to say something went bad

it's going to hit a point where all

these allocations are going to fail and

if we really wait for it it is going to

end and we're going to see that it's

let's try and hit ctrl c and terminate

it because we don't want to wait for

down to 100 and increase this number

let's see if that actually works so

we're going to boil for now we just want

to see that the program is not really

so we're going to run rooster and you

it's going to keep running and at some

it's going to fail to allocate memory

and it's going to say something went

wrong but if you keep going down you're

going to see that the program is ending

so what is happening here is that

the new operator actually failed

but we code the problem and could handle

it in here so what is called handling

you're going to handle it in whatever

makes sense in your program if we were

for example trying to set up a color in

widgets in your application and the

color fails and you fail to set up the

color you may show your user interface

in black and white and keep running your

program instead of getting it crashed

this is just a way to show you

when new fails this is one way we can

solve the problem so we're going to look

the exception mechanism is the first

so we're going to comment this out

because we're going to see another way

and let's do that we can also use the

std no throw setting on our new operator

allocating for new memory so we're going

to do that and we're going to bring up

we're going to reuse that for this here

we're not going to be using the

exception mechanism so we're going to do

something like this get rid of the try

and catch block but we're going to still

so what we can do is pass the new

operator a parameter and say std no

throw and when we do this if new fails

we are going to get no pointer stored in

data here so we can check this against

data is different from null pointer

and we can do whatever we want to do we

get it allocated and we can try and

so what we're going to do is run this

through our compiler through gcc

and you're going to see that the world

is going to be good and you see that

visual studio code was giving us a

squiggly line because it can't really

understand this but this is going to go

through the compiler and it is going to

so let's try and run this program

we're going to ignore visual studio code

for now because the world was good we

could build with gcc and we saw that

this was welding successfully so we can

let's clear properly and run rooster and

it's going to say data allocated a few

other times and the program is going to

end you see that the program is not

crashing because we are also handling

the problem but we are going through a

new mechanism to do that and that's

using the std no throw option with our

new operator here this is really all we

set out to do in this lecture i hope it

is very clear that the new operator can

fail and you have a couple of options at

your hands to handle things when new

fails you can either go through the

exception mechanism by using try and

catch blocks like we did here or you can

use the std no throw option we are going

to stop here in this lecture and the

next one we are going to learn about no

go ahead and finish up here and meet me

there in this lecture we're going to

explore the concept called null pointer

safety and this is a series of measures

you take to make sure that when you are

using a pointer it contains a valid

address if you don't have a valid

address inside you don't use that

pointer and we do that through a series

of checks we can do against the null

pointer for example here we have a

pointer that is initialized to null

implicitly through braced initializers

and what we can do is check if p number

null pointer and this is how we say it

in c plus and if it contains no pointer

we're not going to use it we're going to

say it points to an invalid address this

is something you can do it is simple in

nature but it is going to save you lots

of trouble this is one version we can do

this on but we can also directly plug in

p number and use it like this if it

contains no pointer we're going to get

the message printed out that we have an

invalid address if we have something

other than no pointer we're going to

have a valid address and we can do

something with that this is going to

work because a pointer can also be

implicitly converted into a boolean

expression that our if statement expects

here and it is going to work exactly how

we want here so we're going to see this

in a minute when we hit visual studio

code before we do that though i want you

to be aware that you can call

delete on a pointer containing no

pointer without doing the check here it

is going to be okay we have seen many

rules about pointers and many students

will develop an intuition that you have

to check for no pointer before you do

anything on your pointer and they even

do that before they call delete i have

to break it to you that it is safe to

call delete on a pointer that contains

null pointer so you don't need to do

something like we have here say and

check if p number one and then delete p

number one and reset that to low pointer

this is really overkill you can call

delete on the pointer and it is going to

be fine even if it contains no pointer

now we're going to go to visual studio

code and see these things in action here

we are in our working directory the

current project is no pointer safety

we're going to grab our template project

and we're going to put that in the

current project that we are interested

and we are going to open this in visual

studio code open folder and we are going

to put in a verbose no pointer check

what we are doing here is nothing new we

have a pointer called p number it is a

pointer to ant and it is initialized to

null pointer through implicit

initialization here using braced

initialization and we are checking to

see if it contains null pointer if it

we're going to say it contains an

invalid address if it doesn't we're

going to say that it has a valid address

and you see that we are using a negation

here you can do this however you want if

with gcc let's see what we get

the vote is going to go through

and if we run rooster we're going to see

that p number points to an invalid

null pointer but if we try and set up a

new variable for example and say p

and let's use dynamic memory we have

learnt about that and initialize that

with a 7 for example and when it points

to a valid address we're going to print

whatever is in there we know how to do

that so we can say p number and we're

going to print whatever is inside and

say p number through the reference end

and we're going to say stdndl now the

pointer is not going to contain

no pointer because it contains the

of the memory that was allocated on the

but once we do that we have to remember

to release this memory so please

remember to release your memory after

you are done using it so we're going to

say delete p number after that and we

need to reset it to no pointer in this

case it really is useless because nobody

is going to be using this pointer

anymore the program is about to end but

it is a good practice to do this even in

this case because once this way of doing

events is burnt into your memory it has

become your habit you're going to be

writing cipher c plus plus code now

we're going to try and run this so we're

going to build again the bold is going

to go through and it is going to say

we have a valid address in memory which

is this guy and what is inside is a

seven and now we are writing cipher c

plus plus code through null pointer

safety here we can also do a direct

check using p number without checking if

it is equal to null pointer because this

is verbose but it is something you will

see in practice you can also do

something like this and say if p number

and you're going to get exactly the same

thing so if we have some valid

address inside we're going to print

that let's print the same thing as

and if we build and run we're going to

clear because the world is good let's

clear and run rooster you see that we

get exactly the same thing and if we

didn't initialize this guy with the new

dynamic piece of memory we're going to

get that the memory is invalid the

address we have in the pointer is going

to be invalid and we're going to print

that out through our code here

okay the last thing i want you to see is

that it is okay to call delete

on a null pointer and we're going to say

that here so we're going to go down here

and put in a piece of code we are

setting up a new pointer p number one

initialized with no pointer if we call

delete on it this is going to work

really well and you're not going to get

a crush or anything this is valid c plus

plus code so if we're trying to compile

this it is going to work fine and you

do a no pointer check before you delete

like this because that's overkill you

see that the program both successfully

and we can clear and run it and we're

going to get exactly the same things we

had before so some people are going to

they're going to check for no pointer

and they're going to say if p number one

for example is not equal to no pointer

and they're going to say something like

delete here and they're going to do

and this is going to work but it is

really overkill you don't need to do

this test because it is safe to call

delete on a pointer even if it contains

no pointer in the first place so you

don't need to do things like this this

is going to work just fine don't be

afraid to call delete on a pointer

because it might contain null pointer

this is really all we mean by null

pointer safety and i hope i gave you a

few examples to make this pretty clear

we are going to stop here in this

lecture the next one we're going to

go ahead and finish up here and meet me

there in this lecture we're going to

and a memory leak is when you have lost

access to a piece of memory that was

dynamically allocated to your program

you basically lose the pointer that was

pointing to that dynamically allocated

piece of memory here we have a few

examples of that for example here we

have p number which contains a

dynamically allocated piece of memory

which is going to contain an integer

it's going to be 4 byte the value inside

is going to be a 67. this p number is

our only key to manipulate that memory

and it is the key through which we even

go to release that memory and return

that to the operating system but notice

we are setting up a new number variable

it is an integer and it is allocated on

the stack because this is a local

variable it's not a pointer it's not

dynamically allocated and we take the

address of number and assign that to our

pointer the moment we do that

we have no way to release the memory

that was allocated to p number in the

and if we do that the operating system

is going to think that this memory is

ours but we don't have a way to release

this memory anymore because the pointer

helping us access this memory has been

repurposed to point to this number

variable here i hope you see that

and the memory leak is something like

this when you lose the pointer that

would otherwise be used to release the

memory and your program is basically

going to keep using this memory and the

operating system is not going to have a

way to reclaim this memory so it is

useless so you are no longer using this

memory because you can't access it and

do things with it and the operating

system can't use it either because it

fences your memory hopefully you can see

that this is a really bad situation and

you should avoid these things in your

application so do avoid memory leaks

this is one situation in which we can

have a memory leak here is another

example where we have double allocation

we have a pointer p number one it is

pointing to dynamically allocated memory

again and the value inside is a 55.

if we use this pointer to allocate new

memory the first memory that we were

pointing to is going to be leaked

again it is the same thing we have lost

access to the first memory now we are

pointing to the second dynamic

memory that was allocated to contain the

44 here and again this is a memory leak

your program has lost access to the

memory containing 55 here and the

operating system also thinks that you

are using this memory because you didn't

explicitly return it to the operating

system through the delete operator again

memory leaks are bad do avoid them in

your programs here is another simple

example of a case where you might have a

memory leak you go in a nested scope

like this and allocate a new piece of

memory dynamically of course and point

to that through p number two here but p

itself is a pointer and it is a local

variable nested in this scope

when this scope ends p number two is

going to die but the dynamic memory

itself is not going to die you just lost

access to it and you can't access it

again this is a memory leak and you

should avoid this in your programs

memory leaks are really bad and in

extreme cases they might even lead to

your program crashing if your program

keeps running for an extended period of

time think of programs like those

running in servers for example they can

even run for three months without

stopping and if your program is

increasingly leaking memory the

operating system is going to think that

you are taking too much hip memory it's

going to terminate your program like we

in the lecture where we learned on

conditions where the new operator failed

so if you allocate too much memory then

your program can really take the next

operations you're going to do with new

are going to fail and your program is

going to terminate the message here is

memory leaks are bad you should avoid

them in your programs and whenever you

think that you're no longer using a

piece of memory make sure you delete it

and return it to the operating system

you're going to be writing much safer c

plus plus code we're going to head over

to visual studio code and actually try

this here we are in our working

directory the current project is memory

leaks we're going to bring in our

and we're going to put them in place in

the lecture on memory leaks and we are

going to open this in visual studio code

we are going to clean this up a little

bit bring this up here we have a

variable called p number it is a pointer

to end and we initialize that with the

address of a piece of memory that is

allocated dynamically on the heap we

store a 67 inside and here down you see

we set up another variable on the stack

again this says a stack variable

it lives on the stack it's not on the

heap and we text the address of this

thing and assign that to our pointer

here the moment we do that we have no

more way we can access this dynamic

memory and we have leaked it and this is

really bad the thing is this program is

i don't think compilers have a way to

stop you from making mistakes like this

so you really have to be careful and

make sure that you are not leaking

memory in your program so if we run this

program it's going to run it's going to

run and finish let's say that it is

ending well okay so we're going to build

and see this run the build is good so we

can clear and run rooster and we're

going to see that the program is ending

leaking memory here because the

dynamically piece of memory that we

wasn't released to the system and when

we did this assignment here we just lost

access to it so the operating system is

going to thank this memory belongs to

this program that is ours here but your

program is either not going to be using

this piece of memory because we have

that would allow us to go and do

something useful with this memory here

so this is something bad and you should

avoid it the second example of memory

leaks is when you do double allocation

on a pointer for example here we have

pin number one again and we are going to

of a piece of memory that was allocated

dynamically on the heap the value inside

is going to be 55 but we are using this

pointer again to make it point to a new

piece of memory containing the address

of the newly allocated piece of memory

on the stack on the heap i mean and this

is really bad because again once we do

this we lose access to this memory here

the program here is not going to have

access to it and the operating system is

going to thank we own this memory and it

is going to be bad and uh down here

maybe you can go and say delete number

one p number one but this is not going

to release the memory here it is going

to release the memory here with the 44

and the memory containing 55 here is

going to be leaked let's be good c plus

plus citizens and reset our pointers

after we delete so we're going to say p

number one equals no pointer and we are

going to be playing it safe here and

again we just lift memory here and it is

something you should avoid in your

programs if you run this program it is

going to run just fine so let's see that

because i don't want to leave you with

if i run rooster again it's going to end

well but it is going to be leaking

so we don't want to leak memory avoid

this like a plague we're going to

and show you that you can also leak

memory when you have some nested scopes

in your programs okay let's go down here

and put that in and here is a simple

example we have a nested scope nested

inside the main function and inside the

scope here we are setting up a new

and it is going to be pointing to

dynamically allocated memory and that

memory is going to contain a 57.

the only key we have to this dynamic

memory is this p number two pointer here

but this p number two pointer lives on

the stack itself so when the scope here

is going to end p number two is no

longer going to be accessible and the

memory is going to be linked if you

really want to play it safe you can go

do whatever you want with the dynamic

memory and when you are done with that

you can delete that piece of memory here

while you still have access to p number

in the scope where this thing was

if you hit the end of this scope you're

going to lose access to this pointer and

you will be losing access to this

and you're going to be leaking memory

because you're not deleting it even if

you want to delete it you won't be able

to do that because you don't have a key

that is going to lead you to that

dynamic memory so if we try and do

delete p number two here this is not

going to compile because we don't have

access to p number two p number two is

scoped inside this nested scope here

this is what i mean so be sure you are

aware of this memory leak problem the

cases we have seen here are really

extensive enough to give you an

intuition on how this is bad and you're

going to be avoiding this new programs

and you're going to be on your way to

become a better c plus plus developer

this is really all we set out to do in

this lecture to learn about memory leads

show you a few examples of them i hope

now you understand them we are going to

stop here in this lecture and the next

one we're going to learn about

go ahead and finish up here and meet me

in this lecture we're going to look at

dynamic arrays and these are arrays you

can allocate on the heap and they're not

going to be stored on the stack like we

have seen before the arrays we have

learned about so far have been living on

the stack we want to see how we can

allocate arrays on the heap if we happen

to need that in our applications arrays

are allocated on the hip with the new

operator we can also use the sdd no

throw version of the new operator if we

don't want exceptions in our c plus plus

programs here is a simple example of how

you can do that we have a pointer called

p salaries it's going to be a pointer to

double and it is going to contain the

address to the dynamic memory that we

allocate on the heap which is going to

of doubles of this size here okay this

is an array that is going to be

initialized with junk values because we

explicitly so this is something you need

to be aware of okay p students is also

going to be containing the address of an

array that is going to be allocated on

the heap we are using the sdd nothro

version of the new operator because in

this case for example we might not want

exceptions and we're going to say that

it is an array of events it's going to

be this size but we are using breast

initializer so this is going to be

all the values inside are going to be

initialized to zero this is what we mean

here we also have a p scores array we

are using the std no throw version of

new and it is going to be this size and

initialized with one two three four five

the array is bigger than five the

remaining slots are going to be

initialized with zeros just like we saw

with the arrays we have learned about

previously that we're stored on the

stack this is really how you work with

these things and i hope it is super

clear again we are calling the new

this is going to allocate however memory

space is needed to store these things on

the heap so if this array is going to

contain 10 elements we're going to

allocate enough space to contain 10

double elements on the heap and we're

going to be pointing to that with the p

salaries pointer that's what we mean

here once you have your dynamic array

allocated on the hip you can try to do

things with it for example we can try

and loop through the squirrels and print

them out here you see that we are using

the angle bracket syntax and the

pointer arithmetic syntax it is going to

work equally well you can choose

whatever you want but i just wanted you

to see that you can use both versions

here the next logical thing to think

about when you talk about dynamic memory

allocation is how you release the memory

to the operating system when you're no

longer using it and this is the syntax

to do it with arrays you say delete you

put angle brackets and you say the

pointer that was used to allocate that

memory in the first place and after you

do that you have to remember to reset

the pointer to null pointer because you

are a good c plus plus citizen and this

is really all we had to say in this

lecture this is how you dynamically

allocate a raise on the hip before we

head over to visual studio code and play

with this though i want you to keep in

your mind that arrays you allocate

dynamically on the heap are very

different from the arrays that we have

learned about before and that's because

they don't work with std size and they

don't work for range based for loops

and that the reason for all these

limitations is that when you do

something like this the array really

decays into a pointer and it loses

information that would otherwise be used

to deduce the size that is used by sdd

size and there are other things that are

used by the range base for loop that

they lose when you store and refer to

them using a pointer like this that's

why we have this limitation keep this in

mind if you are using a dynamically

allocated array on the heap you're going

to be using other techniques to deduce

its size and it is not going to work

with a range base for loop so we will

have to use other kinds of loops that we

have learned about in this course and it

this is really all i had to share in

this lecture now i think it's time we

went to visual studio code and actually

here we are in our working folder the

current project is dynamically allocated

we are going to grab our template files

and we're going to put that in the

current project and open this in visual

studio code like we always do and we are

going to go down and put in some starter

code we can play with here we're going

file icon to remove this pane

and we're going to try and show the code

here and again you see that visual

studio code is freaking out when it sees

the std no throw version of the new

operator here but it is going to work

when we hit the compiler okay so we are

allocating three arrays on the heap

dynamically and we are going to be

storing the addresses to these arrays

and these pointers for example p

salaries is going to store the address

to this dynamic array which is going to

be leaving on the heap and it is going

to be the same case for p students here

and p scores i don't think there is much

to explain here because we have already

learned about arrays we know about the

size of an array we know that it is a

piece of contiguous memory location that

is going to be storing variables of the

same type this is really what we're

so let's try and compile this and see

that it actually goes through our gcc

compiler and it is going to work fine

and another thing you should notice is

that this is really compiling even if

what we are using to store the size of

the array is not const remember for

stack arrays or static arrays that we

we had to make sure this guy here is

a requirement and if you didn't fulfill

that your code wouldn't compile now you

see that with dynamic arrays the code is

actually compiling even if it's not cost

and this is something you should be

aware of let's build this again i just

and the world is good if we go down and

run it we're not going to see anything

really because we're not having any

output in this program but this is how

space for a dynamic array on the heap

now let's try and print some of the data

in this course here let's go down here

and actually do that we are going to do

a no pointer check because we want to

make sure that memory was actually

allocated for the p scores array

and after we do that we're going to loop

and we're going to be printing whatever

element is at each iteration the index

at each iteration and you see that we

can either use the angle brackets

notation or the pointer arithmetic

notation it is going to work equally

let's bring up our terminal we haven't

opened one and let's go down and clear

and we're going to be printing the data

first using the angle brackets notation

second using pointer arithmetic and you

see that it is working pretty well

one thing you should have noticed now is

released the memory that we have

allocated here and this is something

really bad so we're going to see how we

can do that we have allocated space for

salaries p students and scores so let's

go down and do that and we're going to

and we're going to have angular brackets

because this is an array we are

releasing memory for or to be exact a

dynamic array which was allocated on the

and we're going to reset that pointer

to no pointer because we are good c plus

plus citizens so we're going to do that

no pointer and we're going to do the

space for a dynamic array so the angle

the square brackets i should say and we

are going to delete p students i think

yes so we're going to say p student

and we're going to say p students and

we're going to reset this to no pointer

and we're going to do the same for p

let's grab this here that's what we want

no that's not what we want we're going

to say delete and say square brackets

ourselves and we're going to say p

scores and we're going to release that

and reset this to null pointer now we

are really playing it safe and our

program is going to release the memory

that we allocated in these three

if we build the program it is going to

go through well so we're going to build

and run rooster and it is going to run

pretty well you see that for peace

we initialized the first five elements

and the remaining elements were

implicitly by the compiler to zero and

you can see that here i don't think i

explained this but this is my chance to

explain this i hope you understand the

next thing i wanted to explore before we

close this video is the difference

between static arrays and dynamic arrays

a static array is an array you allocate

on the stack like we have been doing

before and you do it using a syntax like

let's say scores why not and it is going

to be an array that says it is going to

and we are going to put in our values in

and we're going to go all the way to 10

let's put in a 10 here and we're going

this array is cool and you can loop

through it you can do all kinds of crazy

things with it but i am going to

emphasize two differences we have with

dynamic arrays one is that this guy is

going to work with sdd size so we're

okay this is going to work if we compile

we're going to get a good world at least

i hope yes the world is good and if we

we're going to get scores the size is

the other thing is that you can use a

range based for loop to loop through

this guy here so for example we can say

auto score s for score in scores

and it is going to work so let's go down

and say what we are doing here or we can

even say a single line to separate fence

here i don't want to be confused so i am

going to do something like this so that

i know where my output here is going to

so i am going to build this

with gcc of course the world is going to

i am going to see that the size is 10

and i am going to print my elements here

okay let's see how these things behave

when we use a dynamic array we are going

to set up a similar array but on the hip

which is going to leave on the hip this

array here is the static array in that

it is going to live on the stack you

have to be aware of these differences

okay we're going to do another one which

is going to leave on the heap and the

way we do that we say end pointer let's

say p scores one to make sure this is

different from p squares that we have on

top here and we're going to have 10

elements inside and we can even

initialize this guy exactly like we are

doing here but the data is not going to

leave on the stack the data is going to

if we do something like this first let's

make sure that the code compiles we're

and watch the compiler output here the

bolt is good so this is valid c plus

we can try and use hdd size on that and

we're going to go down and do that

and if we do that we're going to say p

one size and say p scores if we try to

pass this pointer here you're going to

see that visual studio code is going to

freak out because this won't work

array here has decayed into a pointer

when we refer to it using a row pointer

like this so we can't really use it

so if we look at this we're going to get

a weird compiler error but this is going

okay so you can't do this with dynamic

arrays this is one limitation the other

is that you can't use dynamic arrays

like we are using a range based for loop

here so if we grab this loop and try to

work with it on p scores for example

this is something somebody might want to

pscores1 okay and try to print something

inside you're going to see that this is

not going to work the compiler visuals

video code is not going to like it first

and if we try and run this through gcc

we're also going to get a weird compiler

arrow and the problem is going to be

that p scores is really not an array it

is just a pointer that is pointing to

some location in memory that's all it is

and it doesn't have information that

could be used otherwise to loop through

like we can do for a real static array

that is leaving on the stack again let's

be super clear here and say that this

on the heap you have to understand these

things but this is really not a big

limitation because you can store the

size of this guy in some variable and

refer to it if you need that and you can

loop through the array exactly like we

did here using size and it is going to

work pretty well so don't be afraid to

store your arrays on the heap if that's

what you need in your application it is

going to work pretty well you just have

to be aware of some limitations that

come with doing things this way here

this is really all we set out to do in

this lecture i hope you have a better

idea about dynamic arrays you set them

up like this the size here doesn't have

to be cost like we have with static

arrays and they have a few differences

compared to static arrays that were

stored on the stack and that std size

doesn't work for them and they don't

work with range based for loops other

than that dynamic arrays are ridiculed

and you should use them when that helps

whatever it is you are designing

welcome to this new chapter where we are

going to be talking about references

references are a way you can set up

alliances for your variables and have

other variable names you can go through

to modify that same variable for example

here we have a variable called var it is

an integer it leaves at this address

here and the value inside is 33.

if we set up another alliance to it as

var elias we can go through this var

elias variable and use it in pretty much

the same way we use the original

valuable and this is going to come in

handy in many situations as we are about

to see in this chapter we are going to

start in the next lecture and see how we

can declare initialize and use

go ahead and finish up here and meet me

there in this lecture we're going to see

how we can declare and use references in

our c plus application again a reference

is an elias variable that you can use to

reference an original variable and use

that reference in pretty much the same

way you use the original variable let's

see how that can work in c plus plus

here is a simple example we have two

variables one is an integer we have 45 n

the other is a double we have 33.65

we want to set up references to this

variable and the syntax is ridiculously

for the edge value its reference is

going to be something like ant ampersand

you put the ampersand symbol you say the

name of the reference and you initialize

this with the value in the variable that

you want this to reference so reference

to h value is going to be referencing

our integer here and we can use this

name to reference this variable here and

it is going to be like we are using the

original variable which is interval here

we're going to see how this works in a

minute we can do the same using

assignment initialization and down here

you see that we have an example for the

double value and we have a reference to

it once we have these references we can

the original variables for example if

you come here you see we are printing

stuff out if we print any value we're

going to get the value printed out if we

print double value we're going to get

the value printed out we can also print

through references you're going to see

that they are going to print exactly the

same value as we have in the original

but the interesting thing is going to be

if you print the addresses through the

original values and print the addresses

through the references you're going to

get the same addresses printed out which

is really going to say this to variable

names are almost exactly the same thing

in c plus plus and this is really cool

you can use the reference as if you are

using the original variable name in your

c plus plus code we're even going to try

and go through the sizes and print them

out and you're going to see that they

are going to be exactly the same thing

and we are going to see how important

this can become in c plus plus code as

we go through this chapter okay now that

we have the reference declared we can go

through that and modify the value and if

we do that the changes are going to be

reflected in the original variables and

if we print stuff like this again we're

going to see that the changes are going

to be reflected in the original

variables okay if you modify the

original variable the changes are also

going to be reflected in our references

and this is exactly what we would expect

from our references okay so this is

really all there is about references

they are alliances to your variables and

you can use them pretty much the same

way you use your variables let's head

over to visual studio code and see some

of these things in action here we are in

our working directory the chapter is

references and the lecture is declaring

and using references we are going to

and we're going to put them in place and

we are going to open this in visual

studio code we are going to set up a new

variable let's call this data or it's

data this is going to be much more

descriptive and we're going to

initialize this with a 33 why not and

we're going to do a double and say

double data and we're going to put in a

and we're going to set up references to

and again a reference is an elias that

you can use in pretty much the same way

you use the original variable so we're

going to set up a reference to int data

reference mean reference by putting the

ampersand symbol here and we're going to

yeah and you initialize that

with the variable name you want this

and uh here we want to reference into

data so we're going to pass in into data

and this is going to be it our reference

is declared we can do the same for

double and we're going to say it's a

reference we're going to say rough

double data and we're going to reference

devo data here so let's do that okay

let's bring up our terminal and see if

we can compile this code here we're

going to compile with gcc like we always

do and let's close this then on the left

some of the space here the world is good

so this syntax is valid c plus plus

so what we can do is read values from

all these things and show you that they

really are the same things so we're

going to print stuff out and i am going

to put here some code and i am going to

come back when i have typed this i don't

want you to suffer watching me type

these things okay here i have the code

type down and you see that i am just

going to print dana through the original

variables i am going to print the actual

data and print the address of the

variable and do the same for the debo

data which is of type double

how convenient and we're going to print

references we're going to print the

reference and the address of the

reference and we're going to do the same

thing for our ref devil data here let's

so we're going to run the task to do

and we are going to clear the book is

good and run rooster if we run rooster

you see that let's put a separate end

line here so that we see the entire

i really like to see my fans easily

so let's do that and build again okay

the build is good we can clear and run

rooster now and we're going to see the

original data and data is 33 the address

is this guy here we have demo data the

value is 55 and this is the address if

we look at our references we have

exactly the same thing the addresses are

even the same it really is like we are

using the original variable and this is

really cool it can allow you to pass

using references and whatever you are

using when you have sent this data for

example to some other file or some other

function you're going to be

affecting the same data okay so you're

not going to be making copies and we're

going to see how cold this can be

especially when we get to working with

functions this is going to be super cool

okay now we have seen that the

references are really referencing the

original values let's try and modify the

the original values and see that the

references are going to pick up the

changes let's do that we're going to

take 80 data and change that to

111 and we're going to take the apple

why not and after we do this we're going

to print data again so we're going to

use that again here and we should see

so we're going to weld with dcc the bolt

as you see here and if we clear and run

the value is 55 let's put a separation

line in here this is cramped and it is

really hard to see what is happening

here so i am going to put an std endl in

here and weld again so let's do that and

the book is good so we can clear and run

rooster again and now we see things

separated out and it is easier on the

eye here we have empty data to b33 and

the depot data is 55 and we are going to

print our references which are going to

pick up the same things because a

reference is really analyzed to

the original variables but if you go

down you're going to see that the data

has actually changed and together has

and nabodana has changed to 67.2

and the interesting thing is that the

references have also picked up those

changes because they really are

referencing the same things in memory

it's like we are using the original

read these things like we are doing with

references here and this is really cool

here we have used the original variables

to modify data but we can also modify

the data through references and the

original variables are going to pick up

those changes so let's do that we're

going to say ref data and we're going to

1014 or 12. this is going to do we're

going to do ref double data and put in

another large number let's say 1000.45

why not and we're going to print the

data again so we're going to grab

this and print stuff out again so we're

going to go down and put in the code to

print stuff and you see it's going to

use the original variables and the

references and we should see the changes

reflected in our terminal here

and we're going to weld with gcc as we

the bullet is going to be cool we're

going to clear and run rooster we're

going to see that we have 33 and 55 the

references are going to pick that up

that's what we have here we're going to

111 and 67 through the original

variables and the references are going

to be picking that up and we're going to

use references and modify data you see

that the original variables are also

picking that up because we are really

modifying data in the same memory

location that's why these changes are

being shared between references and the

original variables and this is really

all we set out to do in this lecture to

show you how you can set up a reference

and prove that the changes we do either

through original data or references are

reflected between these two guys meaning

references and the original

we are going to stop here in this

lecture in the next one we're going to

do a comparison between pointers and

references because they seem to be doing

go ahead and finish up here

and meet me there and this lecture we're

going to be looking at the similarities

and the differences between references

and pointers okay we know that a pointer

is really something that is going to

store the address of the variable and we

can go through that pointer and modify

the original variable or really do

things with that but in the last lecture

we saw that we could also do the same

thing with references so why have these

and what are the differences between

them here is a simple slide that i put

together to put the important points

about references and pointers together

the first thing is that if you use

references you are not going to go

through the star symbol to the reference

and get to the value you are

manipulating so that's going to really

feel like you are using the original

variable but with pointers you are going

to go through the referencing so that's

another thing about references is that

you can't change them to reference

something else later but with pointers

we saw that we could do that we can

change a pointer to point somewhere else

if it happens to be a non-const pointer

the other thing is that for references

you have to initialize them at

declaration you can't declare a

reference and not initialize that if you

do that you're going to get a compiler

error and we're going to see that in a

minute but for pointers you can declare

a pointer and not initialize it and it

is going to just contain a junk address

and if you try to use that uninitialized

you are going to be setting yourself up

for trouble so we saw that so these are

the main differences between pointers

and references and now we are just going

to be looking at how these translate in

code here is a simple example we have a

variable called double value which

happens to be double and we have a

reference to it and a pointer to it so

you already know these concepts

now if we want to read the value in here

through our pointer and references we're

going to be using two different syntaxes

if we go through the reference we can

use this reference variable name

directly and read the value or change it

ref double value to print that out this

is going to work but if we want to go

through the pointer we will have to go

through the referencing and this is

you know sometimes people don't like

this syntax they think that it is not

direct enough so they prefer to use

references to do these kinds of things

but pointers are still important as we

will see later as we progress in the

course so this is one difference with

references you don't have to go through

the dereferencing mechanism to use this

star here to print stuff or even

manipulate the data inside you just use

the variable name and it is going to

work with pointers you have to reference

because if you don't the reference

you're going to be referring to the

address stored in this pointer this is

the first difference and we see that the

same applies if we are trying to

write data into our variable if we go

through the pointer we will have to

dereference and use this dollar symbol

if we are using a reference we can do

that directly as if we are modifying the

original variable so this syntax is much

more readable the other difference is

that we can't make a reference

reference something else but we can

change a pointer to point to something

else let's look at an example here we

have ref double value which is a

we are doing an assignment to this thing

here we are saying either double value

to our reference but what we are doing

here is not making ref double value

reference this other variable we are

just grabbing the value in other double

value and assigning that to our

reference and the value in either double

value is going to be reflected in the

original value here so this is what we

are doing we are not reassigning to our

reference to make it reference something

else we are assigning the value to the

reference as it is now and it is going

to be still referencing the same

variable in memory if you print out the

address in memory you're going to see

that the address of the reference here

hasn't changed so this is something you

should keep in mind but we know that a

pointer can point somewhere else if we

have a pointer here for example p double

value we can reassign it another address

and make it point to that new address so

in this regard we can think of

references as cost pointers because cost

pointers can't also be made to point

somewhere else and if you're trying to

do that for example here we have a cost

pointer it is called cost p double value

and if we try and make it point

somewhere else through this assignment

here we're going to get a compiler error

okay so this is really all in terms of

the comparisons that we had to make

between references and pointers now

we're going to head over to visual

studio code and see how these things

work in real code so here we are in our

working folder the current project is

comparing pointers and references we are

going to grab our template files and put

and we are going to open this project in

visual studio code like we always do we

are going to go down and put in some

starter code and let's align this a

so and we can close this pane so that we

have some breathing room here we have a

variable of double type and we set up a

reference to it and a pointer to it this

is how we do this thanks you already

and we can try and read through

the original variable through the

reference and through the pointer and

see how these syntaxes differ and how

one might be better than the other for

example if we look at how we are using

the reference it's really like we are

using the original value here we don't

have to do reference if we try to print

the pointer directly like this without

the referencing this is going to print

the actual address stored in this

pointer it's not going to print the

actual value stored in the address

pointed to by this pointer i really want

this to be clear so this is the syntax

we can use for reading stuff either

through references or pointers we can

also use these syntaxes to write stuff

into our variables for example here we

can go through the pointer and we have

to the reference and we can go through

the reference to really do the same

thing and we're going to see that our

syntaxes here are going to pick up the

regardless of whether we write through

pointer or a reference because all these

things really are going to be

referencing the same location in memory

let's try and bring up a terminal here

and we are going to world with gcc let's

do that the build is going to be good

and we're going to clear and run rooster

and you're going to see that at first

that's going to be the value we can get

it through original value the reference

or the pointer through the referencing

and the address is this one here

if we change the value through the

pointer we're going to see the changes

reflected here and if we change the

value through the reference we're going

to see the changes reflected in here so

this is how you can use pointers and

references to do these things here and

you can really choose what makes sense

for your application they mostly do the

same things but some people say that the

syntax to the reference the pointer here

is really ugly that's why most people

prefer to use references like this but

references have other benefits as well

as we're going to see as we progress in

the course another thing i want you to

see is that you can't change a reference

to reference something else in memory

for example here we have our reference

which is ref double value if we try and

make it reference something else

we're not going to get that result let's

so we're going to set up another double

make our ref double value reference this

the syntax that comes to mind is saying

double value and assign that the some

double value here now let's see what

happens if we do that we're going to try

and print whatever we have in memory

ref double value here let's grab this

and go down here and say that we are

changing the reference making the

reference reference something else let's

say that so if we try to build this

let's see what we get we're going to run

and we're going to try and run this

clear not clear and we're going to run

the last line of output here say 78.45

but the address is still the same so we

are still referencing the same memory

with our reference and what we just did

here was just grab the value in some

and assign that in here but the

reference is referencing the same memory

location it's been referencing so in c

plus plus you don't have a way you can

to make a reference reference something

else the only chance you have to make it

reference something is through

declaration here and that's the reason

you can't declare a reference and not

initialize it if you do that you're

going to get a compiler error so let's

try and do something like this we're

going to take out this double value and

the moment we do this you're going to

see that visual studio code is going to

be unhappy you see the squiggly line and

it is going to say initial value of

reference to non-cos must be an l value

okay if we take out the initialization

altogether it's going to give us a

better error i think reference variable

requires an initializer so every time

you declare a reference you have to

initialize it and we should do like we

just did before here and we're going to

be fine again you can't declare a

reference and not initialize it if you

do that you're going to get a compiler

error and the reason is that

this is the only shot you get to make

your reference reference something else

okay if there was a way for you to

bypass this and let the compiler compile

this you would never get another chance

to make this guy actually reference

something and it would really be a

useless reference so make sure you

understand this you can't make a

reference reference something else and

if you try to do something through a

you're going to be assigning the value

of whatever variable you have to the

reference you're not going to be making

the reference referencing something else

the reference is going to keep

referencing the same variable in memory

as we have seen here so let's say what

we were trying to do here but we know

that we can make pointers reference

something else so here we have a pointer

this pointer called the p double value

and it has the address of double value

but we can set up another variable

okay so we can make that reference this

other variable here and let's do that

you're going to see that our pointer now

is going to be containing another

which is our new pointer and we're going

the address of some other double value

and if we print the data now and go down

we are going to say make the pointer

point to something else that's what we

are doing here and we're going to say

the same thing here through a comma and

if we print this try to guess what we're

the pointer is going to contain a

completely new address because we can do

and we're going to see our data here

let's make sure we see the entire fan

okay i think this is the data we have

there's no harm in that so we have our

fence that we have seen before but what

is going to be important here is that pw

value now contains a new address

okay so this is really important and you

have to understand that so we made the

pointer successfully point to something

else and if we change the data in the

we're not going to be affecting the data

we have in here in double value we're

going to be affecting the data we have

and some other double value here let's

do that we're going to change the data

through the pointer so we're going to

say p double value and we're going to

and now we can print the data and see

that things have changed in memory and

we can print this to see the differences

here but before we do that let's also

print the address of the original

variable and the address because for now

we are just printing only the address

through the pointer so what we can do

here is grab htdc out and say

address of double volume and we're going

to put that out through htdc out here

we're going to do that and we're going

to print the address of the reference

ref double value and we're going to put

that out as well i'm going to say

and we're going to say std endn and

after that we are going to grab the

entire thing here and print it out after

we modify the value in the pointer

i hope this is going to show thanks in a

clear way so we're going to weld this

with gcc let's do that the build is good

so let's clear and run rooster and what

you're going to see is that

the original variable is living at

which we can see in our reference but

the pointer now is pointing to something

no wonder that the changes we did

through the pointer are not being

reflected in our double value because

are living in different memory locations

i really hope you see that and this is

really all we had to share in terms

of the differences between pointers and

references i hope you have a clear

picture of what these two things are and

we are going to stop here in this

lecture this one we're going to see how

the const key world works with

go ahead and finish up here and meet me

there in this lecture we're going to see

how the const key world can be used with

and again the idea is to set up an alias

to a variable and make it const so that

we can't go through it to modify the

original variable this is the syntax we

used to set up a non-const reference

that we have seen so far so for example

we can say int age put in a value 27 in

this case and set up a reference to age

with the age variable once we do this

riff edge can be used to modify

this edge variable here and whatever is

inside for example we can go through ref

age to increment the age and if we print

the edge now we should get a 28 printed

out because this reference is going to

change these two things at the same time

or another way to say this these two

things age and ref age are referencing

in your computer so if you change one

the other is going to pick up the change

we can also set up accounts reference

and the syntax is ridiculously easy you

say constant reference like this and

your reference is suddenly caused and

you can't go through it to modify the

if you need something like this in your

application this is how you do it you

can also duplicate the behavior with

count references with pointers and for

that we can use a construct like const

end pointer cost this is going to set up

a cost pointer to cost which we can't

use to modify the value that we are

but it can't also be used to point to

something else so this is going to

simulate the behavior we have with

references and you can do that if you

want and please know that we have no

such thing as constant reference cost

this is going to give you a compiler

error because we have no such concept in

c plus plus and my head is hurting right

now trying to think about what this

would even mean and another thing i want

to make clear before we head over to

vg's video code and play with us is that

the const key world is going to apply to

that you apply it to for example here we

have cost reference age which is going

to be a const reference but this doesn't

mean that the edge variable here has to

okay it can be cost or it may not be

cost but the cost here applies to this

variable name constraint age and we

can't go through this variable name and

modify the age if you're trying to do

that we're going to get a compiler error

now we can head over to visual studio

code and play with us here we are in our

working directory the current project is

reference and cost we're going to grab

our template files pretty quick let's do

and we're going to put them in place

and we are going to open this in visual

studio code we are going to review the

references we have seen so far in this

little example here we have the edge

variable it has a 27 inside and it is a

net and we have a reference to it

and this reference is not const so we

can go through this reference modify the

age and if we do that this is going to

work and if we print the edge here we're

going to see that it has turned into a

28 and we can try and print this through

the terminal so that you can see this

for yourself so let's run the task to

and if we do that you're going to see

edge is 27 now it is 28 and we have

successfully modified data through our

but if we change this reference to be

const we won't be able to do that

anymore so let's try and make it a const

if we do that we're going to get a

compiler error if we try to do something

like this because this is now a const

reference we can't go through it to

modify our data here and we're going to

get a compiler error here we have visual

studio called complaining here but if we

ignore that and go through the compiler

we're going to see that we get the same

compiler error we can't implement a read

only reference which is this ref age

here so this is what a cost reference

really is you can't go through it to

modify the data that is being referenced

and another thing i want you to really

understand is that this const keyword

here has nothing to do with the original

variable this is a constant reference we

can't go through it to modify the edge

variable but this doesn't matter if age

is either const or not const the

constants here applies to this variable

name here so this cost h may be cost if

it's cost it's going to work equally

well and we're going to still get a

compiler error here if it's not cost

it's going to be the same the cost we

have on our reference applies to this

reference variable name here this is

what i want you to understand okay this

is what a cost reference really is

another thing we want you to see

is that we can simulate the same

with pointers so let's set up a const

pointer to const on this edge here and

we're going to see that we can have the

same behavior but for that we're going

to have to comment this out because we

don't want noise output and we're going

to go on top here and comment this out

and say what we are intending to do we

can say that we are simulating reference

behavior with pointers and the way we're

going to do that we're going to say

const and pointer cost and we're going

and we're going to initialize this with

our age variable or the address of our

age to be super clear okay so we have

our pointer set up let's try and go

through it and modify the age let's see

what happens we the reference because

this is a pointer and we're going to say

ph and say plus plus or even change this

to another age let's say 45 and if we do

this we're going to get the same

compiler error so if we build this

let's clear here clear not clear

and above again we're going to get

another compiler error saying that we

can't modify something that is read only

assignment of read only location this

pointer can't be used to modify the data

in this age location here so this is the

same behavior with references because

the reference by default can't be made

to point somewhere else we had to make

this pointer also a const pointer

preventing us from making it point to

other locations so this is how you can

simulate references with pointers and

this is really all we set out to do in

this lecture i hope you found it

the main idea was to let you know how

you can work with cost references and

once you have your const reference you

can't go through it to modify the

original data if you do that you're

going to get a compiler error

welcome to this new chapter where we

will be doing cool stuff with text data

we have seen that we can model a

character array and store in a bunch of

characters and we could for example call

this character array message and

manipulate it in memory in this

structure we will see that this is

actually the way text data is stored in

c plus plus and we have a lot of

facilities built on top of this

character already construct to make it

easy to work with text data we will see

that we can use character arrays to

model c strings which are a facility we

use in c plus plus to handle text data

and we will see that there are a few

built-in facilities we can use to

manipulate that we can get the length of

a string we can concatenate strings and

put them together we can copy strings we

can search for data inside strings we

can do all kinds of crazy things but we

will see that c strings are not that

easy or convenient to work with for

example you need to keep track of how

big the string is in memory you need to

also remember to make sure it ends

correctly and we will see the details

about that in this chapter long story

short c strings are not safe or

convenient to work with in c plus plus

and c plus plus provide another type

that really builds on top of character

arrays but it gives us an easier

interface to work with and we can just

focus on storing in the data and doing

stuff with it in our c plus programs and

the big idea about what we're going to

be doing in this chapter is learn about

the facilities we have in c plus plus to

handle text data in our c plus plus

programs in the next lecture we're going

to start and show you how you can

individual characters in a character

go ahead and finish up here and meet me

in this lecture we're going to be

learning about some facilities in the c

that can help us manipulate characters

and here are a few things you might want

to do with those facilities for example

you might want to know if a character is

alphanumeric or if it's a number or a

character you might want to know if it

is alphabetic you might want to know if

it's a blank character you might want to

know if it's a lowercase or uppercase

character depending on what you want to

do in your application of course there

are facilities to check if characters

are digits there are even those that

help us you know transform characters

make them lowercase or uppercase and

these examples here all of these are

cppreference.com so you can go there and

find the documentation here is the same

link opened in my browser you see that

they leave in the cc type library so you

need this included if you want to use

them and you see that there is quite a

bunch of them we are going to cover just

a section of them and i will leave you

to use the documentation if you need to

use any more of these guys our first

example here is going to help us check

if a character is alpha numeric and the

function we're going to use from the c

plus plus standard library is std is l

and you just pass it a parameter of a

character and it's going to tell you if

a character is either alphanumeric or if

it's not if it is alphanumeric you're

going to get a value that is different

from zero which can be treated like a

true if it's not you're going to get a

value that you can treat like a zero and

how do i know this well we can check the

documentation so if i come back to our

and there is a function here is i'll num

i can open it in another tab and it is

going to tell me what this function does

checks if the given character that you

pass as a parameter here is an

alphanumeric character as classified by

it's going to tell us if the character

alphanumeric or not you give it a

character and what you get from it is

the return value here it's going to

return a non-zero value if the character

is alpha numeric so this non-zero value

which is an integer because that's what

we get out of this function is going to

and if this character here is not alpha

numeric we're going to get zero that we

can treat like a false this is really

cool and if you go down here you're

going to find a few examples i don't

want you to worry about this c local

say more about the meaning of the

characters that you are storing in

memory but for now we're just going to

be happy with the defaults and use this

function as is it is going to work

enough well okay here is our function

again so here c is alphanumeric we

different from zero because c is

alphanumeric and the second example here

is not alphanumeric so we expect to get

a value that is equal to zero and we can

use the return of this function

in a test for example we can say a

character we put in a star here it is

called input car and we say f is al num

and we pass this character we're going

to print out this character is alpha

numeric if it's not we're going to print

is not alpha numeric you can do that and

you can do all kinds of crazy tests in

your c plus plus applications here is

another example that we can use to know

if the character is alphabetic so it's

going to return a value different from

zero if the character is a an alphabet

character a through z that's going to

return something different from zero and

if we pass something that is not for

this second line here or the seven at

the third line here we're going to get a

value equal to zero because that's not

alphabetic we have another facility to

help check if a character is a black

character and we see an example that

here we have a character array called

message we have a couple of blanks

inside and we can hunt for them using

the ease blank facility from the c plus

plus standard library here we have a

variable that is going to keep track of

how many black characters are in here it

is initialized to zero and we're going

to loop around okay and we're going to

look by the amount equal to the size of

the message array here we can use std

size again because this is a row array

it is a static array and we can use sdd

size it is going to give us how many

characters we have in this array you

already know this and if we get inside

we are going to try and check and see if

is a blank if it is we're going to print

that out and we're going to increment

our blank account by the time this loop

is done we will have printed out a lot

of blank characters if we happen to

have them in our message and at the end

we're going to say in total we found

however many blank characters this is

if we run this program and hopefully you

this can be in text processing

applications if that happens to be what

you are working on we're going to run

this example in visual studio code in a

minute here is another example that we

can use to check if a character is

lowercase we have an array of characters

here inside we have some text

and we have a few variables to keep

track of how many characters are

lowercase or uppercase we're going to

set up a loop which is going to be a

range based for loop and we know that

we're going to increment the lowercase

count if it is uppercase we're going to

increment the uppercase count this is

and we are going to print that

information when the loop here is done

okay we still have a few examples ahead

the current one is going to check if a

character is a digit if you want to do

that you can use this and we have a

character array here and we're going to

have for digits inside this message here

so we're going to do basically the same

thing we're going to set up a variable

that is going to keep track of how many

digits we have in this message we are

going to loop around using a range based

for loop we're going to check if the

current character is a digit and we're

our variable here if it happens to be

the case and at the end we're going to

say how many digits we found in our

message here it is this simple the last

example we're going to look at is to

help us turn a character into lowercase

or uppercase and here is an example that

is going to help us play with us we're

character array called home the feeling

of belonging and we will set up a

destination character array

that we're going to store whatever we

here you see a loop that is going to

turn our message here into uppercase

and you see we're going to loop around

by this amount the size of original

and we're going to be grabbing each

and turning that to uppercase this is

what std to upper function does the

result of that is going to be stored in

our destination string and by the time

we are done here original string is

going to be however it was but uppercase

string is going to be stored in our

destination array and if we print it out

we should see this thing printed in

uppercase we can basically do the same

thing and turn the string into lowercase

and our destination string is going to

be now lowercase and you're going to see

that this works out pretty well

now that you have a basic understanding

about how these things work we're going

to head over to vg studio code and play

with us okay here we are in our working

directory the current project is

we are going to grab our template files

like we always do and we're going to put

this in place and we're going to open

this in visual studio code pretty quick

and we are going to go down and put in

our first example this example is going

to be using the std is al num facility

and this is going to be checking if the

character is alpha numeric we're going

to see what we get from this if we print

this out we're going to check if c the

character c is alphanumeric we're going

to see what we get and we're going to

check if this character here i don't

know how to pronounce it i'm sorry

we're going to check if it is

alpha numeric we're going to see that

and we're going to use this in at

condition we're going to check and see

if our star character here is

alphanumeric and we're going to print

that out we're going to say it is alpha

numeric or it is not from the

documentation we know that this thing

library so we may want to include that

but it is possible that it is coming

from iostream here that's why we don't

visual studio code complaining here as

an example if we try and comment out

this is not going to make sense anymore

okay so the include needed to use these

guys here is coming from io stream okay

so we're not going to include that here

we are going to open up a terminal

and build this with gcc and you're going

to see that the block is good if we go

down and clear let's clear properly and

run rooster we're going to see that c is

alphanumeric because we have a one the

one can be treated like a true and the

character here is not alphanumeric

and you see that the star here is also

not alpha numeric and we know this

through our test here and you see that

with this facility here if you want to

get true or false from this function you

can turn this into booleans using static

cast but we're not going to do that here

you already know that we can comment

this out for now and look at another

cctype library there are many of these

we're going to look at quite a few of

them we're going to comment this out and

go down and put in a code here and this

is going to check if a character is

alphabetic so if it is an alphabet

a from z lowercase and uppercase

c is alphabetic the character here is

not alphabetic and seven here is not

alphabetic so for the first one here

we're going to get something

not equal to zero we should get a one

that's what they use in most cases for

this we're going to get a zero the

second one and for the third one we're

going to also get a zero this is what we

we are going to build with gcc of course

and we are going to clear and run

and we're going to get that c is

alphabetic this guy is not alphabetic

and seven is not alphabetic if we change

and both again you're going to see that

the results are going to be what we

let's clear and run rooster this is

going to be exactly what we expect but

you see that it is not a one and this is

not guaranteed to always give you a one

it is guaranteed to give you something

different from zero if the character is

alphabetic and zero if not and we can

we can say f sdd is alpha and if we're

boiled the both is going to be good and

we're going to clear and run rooster and

you see e is alphabetic i should put a

space here i do encourage you to change

these characters up and see what you get

here and see how you can use this that's

in tests that's the best way to learn

okay before we continue i do encourage

you to try and run these methods through

different compilers for example here we

also have an msvc compiler from

microsoft setup so we can use that and

try to build this thing here but before

we do that let's bring up our pen here

we don't want to override it we're going

and i am going to remove this and move

and i am going to clear whatever i have

and i am going to go there i am going to

and i am going to choose world with msvc

i am going to use that it is going to

build my thang you see the output here

and it should say that the world is good

in a minute world finished successfully

microsoft is going to give us a lot of

output here but no problem the build is

in our folder here you're going to see

that we have these files one of them is

if we run it we are going to get the

outputs that we expect and you see that

it is exactly the same thing we got

i am telling you to try and use

different compilers because some

compilers are going to flat some of the

or those that start with c as unsafe

because there are some tanks that can

really throw you off about them and

we're going to learn about them in this

chapter as we move forward just know

that it is a good idea to try these

things on different compilers and see

the errors you get and make yourself

for now we're going to move on and we

gcc because that's my favorite compiler

you can use whatever compiler you want

the next example is going to check if

the character is blank let's close this

and give ourselves some breathing room

we're going to bring this down a little

bit and we're going to check if the

character is blank the facility for that

and if it's a blank character we're

going to get something different than

zero and we can use that in a test like

this and if it's not a black we're going

to get something equal to zero and this

test here is going to fail so what this

example here is going to do it's going

to count how many blank characters we

message here and we're going to print

the counter of that on the console using

this line here so let's go through this

loop and see what it does the first

thing we do is initialize blank count to

0 and we are using an integer and

because this is a count i think blank

count is of wrong type because it can be

negative so to really be safe in our

program here we should make this

this is better okay so let's use size

because this is a size and size t is a

good type to keep track of sizes in your

c plus plus programs so make sure you

is go in the loop at each iteration

we're going to check if each character

at each iteration is a blank if it is

we're going to fall in here and say that

we found a blank character at this index

and we're going to increment our blank

account and by the time this loop is

done we're going to have the blank

account stored in this blank account

variable and we're going to print that

now we can build with gcc let's do that

we're going to world with our gcc

and the world is going to be good can

it's going to say we found a blank

and in total we have found nine blank

characters do we have that many let's

count so one one blank character

we have two here we have three we have

eight and nine if you count you're going

to find that we have them and the first

one is at index five so index zero is h

one two three four the first one is at

index five and this is doing exactly

what we want we can go down and check if

a character is uppercase or lowercase we

can do that through an example like this

and the facility is going to be std

lower and std is upper we have a message

we're going to loop around using a range

based for loop and we're going to check

if each character is either lowercase or

and if the test is good we're going to

jump in the loop and we're going to

increment lowercase count which are a

few variables to keep track of how many

uppercase and lowercase characters we

have in here and again these variables

are going to store counts so it is

to use a size t or some unsigned integer

type but now we're going to use size t

because it is good so we're going to

keep this stored in here and we're going

to build this and see what we get

before we run we want to clear

and we are going to build with gcc

the bolt is going to be good we're going

and you see that the original strand is

this guy here what we're going to do

we're going to print whatever character

we are at i'm going to put a space in

front of that and we're going to see

increment this is the output why do we

have this method here because we are

each character and we are not printing

the upper case ones we are printing

lowercase ones that's why you see

this guy here this is really interesting

you can keep this in if you want i am

going to keep this on the important

message is that we found lowercase

characters and uppercase characters and

we have five uppercase characters if we

go in and count we're going to find that

two and three and four and five five

uppercase characters and if you count

the lowercase characters one by one i am

sure that you're going to get a 47 like

we did here we're going to comment this

out because this was just an example

i am leaving this in here so that you

can use this as a reference if you want

we can also check if a character is a

and we're going to use std is digit to

check that the return type is going to

if the test succeeds if it fails we're

going to get a zero and we can use that

like this so we have a message here

stored in the character array called

and we're going to loop around checking

if each character we are at is actually

a digit or not if it's a digit we're

going to say found a digit i'm going to

say whatever digit we found and we're

going to increment the digits count and

we're going to store that information in

this digit count variable here we don't

want to make it an end so we're going to

and we're going to build and run this

and see how many digits we found you

know it is this number here i'm not

we're going to let our program figure

this out so rooster and we're going to

find two two and one so we found three

digits and it is exactly what we expect

we're going to comment this out and show

you another example and in the last

example we're going to be showing you

that you can change the case of a

character if it's lowercase make it

uppercase if it's uppercase make it

lowercase and you can do things like

that we have a message here stored in

our character array called original str

we set up another array which is going

to store our message that is transformed

and we're going to loop around turning

everything we come across uppercase

the way we do that we're going to say

and we're going to pass in the character

that we want to turn to uppercase if we

do that we're going to get an uppercase

character out of that and we're going to

array at this index here it is this

simple after that we're going to print

the original strand and the uppercase

string we should get that printed out

and we're going to do the reverse and

we're going to grab the original

strength loop over it and at each

iteration we're going to get whatever we

and turn that to uppercase to lowercase

and the result of that is going to be

stored back in our destination strand so

we're going to overwrite whatever we

have in our destination string here and

after that we're going to branch the

lowercase string and we should get that

printed out this is how the example

works and if you have any problem

understanding this i am always around

please do ask i will do the best i can

to help you out for now we are going to

with gcc the builder is going to be good

we're going to clear and we're going to

run booster and we're going to see that

the message is here it is turned

uppercase it is turned lower case and

this is how you can do these things here

so we have looked at a few of this

facilities from cctime i don't really

want to look at all of them because that

would be really boring i hope you have

an idea about how they work and if you

want to look at all of them all you have

to do is come to the documentation here

open it up and look at the documentation

and in most cases they are going to have

examples down here that you can look at

for now we are going to stop here in

this lecture this is really all we set

out to do to play with many of these

facilities from the cctype library in

the next lecture we're going to look at

how we can manipulate c strings and by

that we mean concatenating them or

putting them together copying them out

and doing all kinds of crazy things

go ahead and finish up here and meet me

in this lecture we're going to look at

the facilities from the c plus plus

standard library to play with c strings

all of these are going to be leaving in

the c string library you can go and

check it out at cpp reference and we're

going to start and look at a few

examples of some of the things we can do

with this library i mean c string the

first thing we're going to look at is an

example of how we can check the length

of a strength here we have a character

array called message one it is a

character array and you see that we made

it const we also have another array that

is pointed to by pointer you know that

if we do things like this this array is

going to decay into a pointer and there

are a few things we can do with that for

example we can't use it with std size

and we can't use a range based for loop

to loop through this message to thank

sdr then is going to help us check the

length of this thing here so we can use

it for example if we do hdd sdr lam

message one we're going to get the

string here this is not going to count

the null character though so the null

character that is implicitly added in by

the compiler is not going to be counted

in here you're going to see this in a

minute when we hit visual studio code to

play with this thanks but this facility

can work regardless of whether you are

using a row array like this or even for

pointers like this and it is really cool

so we can use it like this we're going

to get it printed out please note that

we can also use the size of operator to

get the same thing so it is going to

work almost the same way but the size of

operator is going to include the null

character you need to be aware of this

the good thing about str lan here is

that it still works for a decade arrays

so if we use it on message 2 we're going

the correct output we're going to get

the number of characters in here which

and we can also try and print out the

message two but here we're going to get

the size of a pointer printed out okay

that's how hdr lan works it lets you

evaluate the length of a strand here is

another example and it is str cmp or

string compare it is used to compare

strings what you're going to do with

this facility is give it two strands c

and one is this guy here l h ace or left

hand string i think that's what this

stands for and we're going to give it a

right hand strand and by the way these

signatures are copied straight from the

documentation so that we can look at

this in one slide to make it really easy

to follow this is going to return a

negative value if the first guy happens

the second guy in lexicographical order

so it is something like a comes in front

of b c comes in front of d or something

like that if the two strands are equal

zero and it's going to return a positive

if the first guy appears after the

okay and we're going to try it out we

have two strings alabama and la bama

here and they are stored in character

arrays that are pointed to by these two

pointers string data one and string data

two and we can do something like this

below here so we're going to print

and we're going to say std string

compare and we're going to pass in the

first string and the second string for

now i want you to pause a little bit and

try to guess what we're going to get

the first string is alabama the second

one is blah blah so the first one comes

and we see that we're going to get a

negative value if the first guy comes in

front of the second guy so alabama comes

and we would expect to get something

negative from this thing we are doing

and again if we try and change them up a

little bit you see that alabama still

so we're going to get a negative value

pointed out and we can change these

things up to see what we get it is

really simple if you know how to use

them we can also use another version of

string compare which is going to let us

specify the number of characters that we

we can specify that we want to compare n

characters in this case it is three

characters and it is going to compare a

section of the strings that you specify

as a first and second parameter here so

for example if we change string that i

want to be a a i a and string data two

to b a a a n c a and we are comparing

three characters in here so we are

comparing aaa to aaa we're going to see

that they are equal and we're going to

get a 0 printed out here you're going to

see that this is exactly the case when

we get to play with us in visual studio

we have a facility that we can use to

search in a string and search for a

character the facility for that is sdr

chr and it is going to find the first

occurrence of a character in a string

and the documentation for this is right

and please note that this example is

straight from the documentation

okay so we have a message here

it is a character array and it is

pointed to by a const car pointer called

hdr and we have a target character that

and the result is going to be stored in

the result character array here and we

have a variable called iterations that

is going to keep track of how many

iterations we did to find our target

here the way this guy works it is going

to return a pointer to what you find

if it is found for example in here if we

find this first t this function here or

this facility is going to return a

if it doesn't find what we want it is

going to return a null pointer that's

how it works and you can see that in the

documentation here we are going to take

advantage of how it works in this while

loop here and the way you use this

facility you give it the strength you

want to search in and you give it the

character that you are looking for so if

we look at how it works in the while

loop here we are going to call the

and we are going to store the result in

our character pointer here and if we go

inside we're going to hit the first

character here at the first iteration so

we're going to find this t here and when

we find it the result of this is going

to be stored back in result here

i hope this makes sense so we're going

to find it we're going to print it and

we're going to increment result to make

it point to the next character this is

pointer arithmetic in action here

and after we do that we're going to

increment the iterations so we should

have one iteration by now and we're

going to jump into the loop again so the

string we search in is going to be

so we're going to try and find

an uppercase tn and it is going to find

this uppercase t here so it is going to

point to it and the pointer to this t

is going to be stored in this result

here okay and we're going to jump into

our body here we're going to say that we

found this t we're going to print it out

and we're going to increment results if

we increment reserved now research is

going to be pointing to the h here

say how many iterations we did to find

our thing we will have printed out the t

that we have found and we're going to

jump to the next iteration which is

in the reminder of the string here it's

not going to find it of course it's

going to return no pointer and the test

here is going to fail and we're going to

fall down here and say how many

iterations we found i realize this

example can be really confusing i am

going to try and explain it again when

we hit visual studio code for now note

that this facility can help you find

characters in a string that's the

message here there is also another

function that helps you find the last

occurrence of a character in a string

for example here we have a character

it is a path to a file on some limit

and we have an output character pointer

which is going to store the pointer to

the character that we found okay if we

find the character we're going to store

in the pointer to that character if we

don't find it we're going to return no

pointer i think that's how this thing

so what we really want here

is to hunt for the file name in this

path here and this is really interesting

so we're going to search for the

backslash the last one and this string

here and it is going to find this guy

here because that's the last occurrence

in our input string here once we find it

we're going to get a pointer to this guy

stored in the output character pointer

here and we're going to print it out

what we're going to do we're going to

use pointer arithmetic to move this

pointer to the next guy because that's

what we really want we want to print

starting from the edge here and that's

what we're going to get when we print

now that we have looked at all these

examples i think it is time we headed to

visual studio code and actually played

with them okay here we are in our

working folder the current project is c

string manipulation that's what we're

going to work on we're going to copy our

template files and we're going to put

and we're going to open this in visual

studio code pretty quick let's include c

string because that's what we're going

to be using many of the things we're

going to be playing with in this lecture

are documented in this piece of

documentation here so you can come here

and get more details than we could even

cover in a course like this let's bring

this up a little bit and we're going to

go in our main function and put in the

first piece of code we can play with the

str land facility is going to find the

length of the strength and it's going to

work regardless of whether you are using

a row array like this or even if you are

using the character pointer to point to

your array and this is pretty cool so

here we have strlen message one we're

going to print that out we're going to

print how many characters we have in

we're going to also use the size of

operator to try and compare these things

but please know that the null character

is going to be included if you use

this is very important to know

but one interesting thing about hdr lan

is that it is also going to work if you

and something that is pointed to by

pointer so even decayed pointers

are going to be usable here and this is

pretty cool so we can also try and print

the size of message 2 which is pointed

to by a row pointer and we're going to

see what we get but we know that we're

going to get the size of a pointer

because that's what it really is message

two here is just a pointer okay let's

and we are going to bring up our

and i try and build this with gcc we're

going to do that so we're going to use

the world is going to go through

and we're going to clear and run rooster

and this is going to give us what we

size of message 1 is 17 because sizeof

the null character htrlen message2 you

that is pointed to by a pointer and this

is really useful if you happen to need

the size of an array like this you can

use hdr then and you're going to get the

size of data in there but know that the

null terminating character is not

counted if you use hdr ln here and size

of message 2 is going to be 8 because

that's the size of a pointer on our

system here so know that this guy is

we are going to comment this out the

next thing we're going to look at is

strcmp which can be used to compare

so it works exactly like we say it's

going to return something negative if

the first string happens to come in

front of the second string in

for example here we have a few variables

we have alabama and blabama there are

and we have a couple of other strings

stored in row arrays like this and by

doing this i want to prove that this

facility is going to work regardless of

how your array or your c string is

stored so we're going to use that here

c string pointer 2 by pointers

we're going to try and compare whatever

with string data two string data one has

alabama string data two has blah blah so

if we compare these guys we expect to

get a negative value out of this thing

because alabama comes in front of

blabama in our alphabet so a is in front

of b so we're going to get a negative

value out of this and we expect to get

the same thing in the second example

here which is going to be using what we

so make sure you understand this and

we're going to try and build this to see

that it passes through our gcc compiler

and run rooster and you're going to see

i want you to play with this thanks and

try and change for example the 8 with c

okay we're going to try and build but

before we do try to expect to see what

you get c comes after blah blah

if we look at this description here we

should get a positive value because

the second guy in lexicographical order

so we should get a positive value

for the first thing that we print here

okay let's weld and see if that's the

case we're going to build successfully

we're going to clear and run rooster and

you see that the first guy prints a one

cla gamma comes before blah blah

and the second one is going to

still be a negative one because we still

whatever we had before in there okay

this is how you work with this thanks

let's turn this back to alabama

working on this and the next piece of

code we are going to try and modify

whatever is stored in string data 1 and

string data 2 and print the comparisons

for example we have alabama and album

and by the way we are able to modify

because it is a pointer to a strength

and notice that this is not the

conspirator so we can really change

where this guy is pointing and that's

what we are doing here but we can't do

that with string data 3 and string data

4 because these are arrays and remember

you can't change where an array points

so this is going to compile nice but if

we try and do the same thing with string

let's do that you're going to get a

so we're going to put this guy here and

and we should see visual studio code

complaining here because this is not

allowed you're not allowed to make an

point to another location and this is

character array or cost character array

in memory that we want this pointers to

point to or this array to point to and

this is not possible so we're going to

get a compiler error if we do this this

is something i wanted you to know that's

why i set up this example here so if we

run this we're going to see the first

or i think i should comment that out

or let's not comment it out now if we

run this program we're going to get the

output for obama and alabama printed out

and alabama comes after alabama so we

expect to get a negative one because the

first guy here comes in front of the

second guy so we're going to get a

thing we are doing here let's try in

the builder is going to be good so we're

going to clear and run rooster and we're

going to see that we have a negative one

here alabama comes in front of a lab

so this is cool so we can try and put in

many other examples for you to play with

i am going to do that because i don't

want to type all this thanks and we're

going to print the results out for

example we put in india and france we

put in kigali and kigali and we're going

to get things printed out here so let's

build this so that we don't waste time

we're going to clear and we're going to

and we're going to see that we get these

things here alakama comes after alabama

india comes after france we get a one

shigari comes together with kigali and

we get a zero you can try and put in

whatever you want these are just a few

examples for you to play with and by now

i hope you really understand how this

function works or this facility works so

we're going to comment it out whatever

so we're going to comment all this out

so that we don't have noise output in

whatever we want to do next and what we

want to look at next is this function

here which is going to compare

strings in the same ways but we're going

to tell it to compare however many

characters in the string and you see

that my string here has been commented

up i can quickly take it and bring it

down here let's do that i can't find

let's find that and copy it down

and we're going to find them here so i'm

and bring that down here so that i can

compare these things so let's come down

here and print and put in our

declarations for this strengths and you

see that visual studio code is happy now

so what we're going to do is compare a

set of characters in these strings here

okay so we're going to compare any

characters in our strengths so we're

going to compare allah to blah here and

allah is going to come in front of black

so we're going to have a negative one

printed out here but if we change the

strengths to aaa and aaa here and

compare the first three characters we're

going to get a zero printed out because

the first three characters are equal and

again the special thing about this

function is that it allows you to

a number of characters you want compared

in these two strings so you can say i

want to compare three strands you can

say i want to compare four strings or

just make sure that you don't go over

the size of the string and if you do

that it's not going to make sense what

you are trying to do here if we go down

here we're going to change n to 5 and

we're going to be comparing all these

things in here and we're going to get

the first one comes in front of the

second one because i comes in front of n

in our alphabet if we change the data to

o is going to come after n and we're

going to get a positive number printed

out here we're going to try and run this

so let's run the task to build with jcc

the bullet is going to be good and we're

going to clear and run rooster

and we're going to see that alabama

comes in front of blabama because we are

comparing the first three characters

if we have aaa in here and we compare

the three characters you're going to see

that they are equal we get a zero

and n here we're going to get a negative

one because i comes in front of n

if we use o here and n we're going to

get a one because o comes after n this

is really simple to understand now that

we know how to use the first version of

string compare this version is just

going to allow us to specify how many

characters in the string we want

compared so we're going to comment this

out and we are going to go down and do

another example that allows us to search

and the method we use to do that is std

so this guy is going to find whatever

target you want to find and if it finds

that it's going to return you a pointer

to dot's target if it doesn't find it

it's going to return you no pointer so

we set up an array here and we store

that in a location that is pointed to by

the pointer to character here and we say

whatever target we are looking for in

this case we want to find this t here

we are going to set up another character

array that is going to store our results

the result is really going to be a

pointer which is going to be pointing to

something valid if we find the target

and it's going to be no equator if we

didn't find the target and we set up

another variable which is going to store

how many iterations we did we should

really make this an unsigned integer or

size t so let's make that here and we're

going to loop here so the first time

we'll open here we're going to call this

guy we're going to say i want to find a

and result here and the result is going

to be pointing to this line here because

we did the assignment here so it's going

to go and try to find the t it's going

to find the guy here at the first index

and the test here is going to succeed

when it succeeds it's not going to be

equal to no pointer it's going to be

and it's going to succeed and return the

pointer to be stored in resort after

this guide returns the pointer is going

to be stored in the result here and

that's going to be a pointer to this

team and we're going to jump in the body

here i really want you to understand how

once we get to the body we're going to

say uh-huh we found our target that's

going to be our t print it out and it's

going to start at this location

okay and we're going to print starting

from the t here because that's what our

result here is pointing to after we do

that we're going to increment the result

to make it point to the next character

if we do that with pointer arithmetic

now we're going to be pointing to the r

i hope this makes sense and we're going

to increment our iterations so we're

going to say we have done one iteration

and we're going to try and run this

again and by the time we get in here

we're going to have this string here in

which we are searching for a t

and it is going to be found starting at

this second t here there here

it's going to store the pointer to it to

resort here or i should say the search

is going to be successful so we're going

to find the pointer to this t

and return it from this function here

and the pointer is going to be stored in

pointer here we're going to jump in the

body and we're going to print we found

the target starting at this t we're

going to print that out and stdc out is

going to print until it meets an old

character so we're going to print this

thing through the end and we're going to

put a slash n which is going to move us

to the next line after we do that we're

and uh result now is going to point to

and we're going to increment iterations

now we're going to have done two

iterations by now and we're going to run

the loop again this time the loop is

going to fail because starting from here

and that this function is going to

return no pointer and this test here is

going to fail okay we are going to

return no pointer no pointer is not

going to be different from no pointer so

this is going to fail and we're going to

fall down here and say how many

iterations we're going to find so in

total we're going to do two iterations

and we are going to find two t's and

we're going to print whatever we find

here make sure you really understand

and i put in this example on purpose

because it is a little complicated but

it is going to really bring your game up

in how you use these functions from the

c plus plus standard library and you

really need to know this if you have any

be sure to ask me i will do the best i

can to help you out so we're going to

build this and run this we're going to

build with gcc as always and we are

going to clear and run rooster and

you're going to see that we are looking

we are going to say we found t starting

at the t here so we're going to say try

okay we're going to print all the

message out and the second iteration is

starting at this location here and we're

going to do two iterations in total

we're going to comment this out and

again if you don't understand this

please go through it again and if you

still don't understand be sure to ask me

i am going to do the best i can to help

you out and some of you might be asking

why did we go through the trouble to

and the explanation i can come up with

is that you don't really want to modify

this guy here because somebody is going

to look at this thing and say

this is the message i have in sdr here

but if you try and modify this in the

loop it's going to be messed up because

you're going to be incrementing it and

doing all kinds of crazy things on it so

you don't really want to modify this so

a better way to even do this is to mark

this as a const pointer and we know how

to do that so we can say cost here and

if you even try to increment htr

somewhere you're going to get a compiler

so let's make sure we see that for

example we try and do plus plus sdr

we're going to get a compiler error

because this is a const pointer by now

we're going to comment this out and show

you something that might throw off many

of you guys so we're going to comment

this out and i am going to bring that in

and we are going to do basically the

and use str in the first place here

okay this is how we're going to do this

we're going to have our string we're

going to have our target we're going to

have our result here which is equal to

null pointer and we have our iterations

which is an integer let's make this a

size t and what we're going to do in

here we're going to use htr to search

okay and we're going to basically do the

same checks we're going to jump in here

and say we found the target starting at

result and we're going to increment hdr

here because it is not a constrainer now

try to go through this thing here and

see how many times you're going to loop

okay go through it and when you are done

we're going to try and run this we're

going to build with gcc the build is

going to be good we are going to clear

and run rooster and you see that this

guy is going to look 25 times

and this is crazy why is this happening

what we really are doing here we are not

assigning the result in this trend that

okay let's try and go through this a

couple of times so the first time we're

going to do our search okay so we're

and if we find our target we're going to

return the pointer to the target

if we don't find it we're going to

return a null pointer the first time

we're going to find this t here okay and

we're going to return a pointer to it

okay so after we do this we're going to

and we're going to say we found t

starting at this location here that's

going to work and we're going to

implement str okay notice that we're not

if we increment sdr it's going to point

to the next character which is r here

and we're going to increment our

iterations and we're going to start in

we're going to search in here

and we're going to be searching from

and we're going to find the t starting

at this location we are going to find

this t here and we're going to

return that and store that in reserved

but the problem is that what we are

incrementing here but the problem here

is that we are incrementing one by one

we are not jumping to this t here and we

by assigning the result into the same

variable that we are searching in okay

so this is going to loop 25 times and it

is not really good and some of you might

try to set up something like this and it

is really not going to be good try to go

through this and you're going to see the

reason why it is looping 25 times okay i

wanted you to see this don't do

something like this and we are going to

comment this out the next thing we're

going to see is how we can find the last

occurrence of the character and this is

a really cool example i like it it is

going to do something very practical we

are going to take a path which is going

to be an array basically stored in this

input array and we're going to strip off

all the things we don't need and we're

going to hunt down for the file name

from a full path and this can be useful

in whatever application you are doing so

we are going to hunt for the last

occurrence of a backslash character

chr facility in the ziploc squad

standard library and you can find the

documentation on this guy here i'm not

going to go there you should really

practice to go there and read what these

things do that's why i am living in the

lens to the documentation you should go

there and read and if you have a problem

you can ask me i will do the best i can

so this line here is going to hunt for

backslash it's going to find this guy

here and we're going to store a pointer

to that in our output character pointer

here after we do that we're going to say

if we found something useful if this is

not no pointer we're going to print that

out but we don't want to print starting

from the backslash we are going to use

pointer arithmetic and move to the next

character which is going to be this h

here so if we print this out we're going

to have hello cpp printed out because

sddc out is going to print until it

the last now character and that's going

to be after the last p here because this

is a c string let's roll here okay we're

going to build this the build is going

to be good we're going to clear

and run rooster and you're going to see

printed out here okay this is really all

we set out to do in this lecture i

apologize that it turned out to be

lengthy these things can take long to

explain and i really wanted you guys to

have as many explanations as i could

we are going to stop here in this

lecture the next one we're going to see

how we can copy and concatenate

c strings using the facilities from c

string here go ahead and finish up here

in this lecture we're going to look at

a few more facilities from the c string

library and those are going to allow us

to concatenate and copy strings over the

documentation for what we're going to be

talking about can be found here if you

go there you're going to fall on this

link here and you're going to

find that c string was originally in the

c standard library as string dot h but

in c plus plus we can use it like this

we have a couple of functions we can

copy stuff we can concatenate we can get

the string length we have seen this but

now we're going to look at things that

allow us to copy and concatenate stuff

that's something you may want to do a

lot the first example we're going to

stdstr cat which is going to allow you

documentation here and see more about

this facility here and you're going to

see all about it for now we're just

going to play with it we're going to set

up two arrays one is going to be called

it's going to contain hello the other is

going to be source here and it's going

to contain worlds notice that these are

row static arrays that are stored on the

and uh that's how we set them up here

okay so we can concatenate strengths

using the syntax like this we're going

to say hdd hdr cache we're going to say

the destination string and we're going

to say the source string we want to copy

from okay so after we do this the

destination is going to contain

these two strings joined together and

before you do this you have to be sure

that your destination strength is big

enough and this is a problem because you

have to really keep track of your

destination strength and it is easy to

put in many more characters that can

really fit in the destinations rank

that's the reason many of these

functions here are considered unsafe by

many compilers i don't think you can

compile this on visual studio it's going

to stop you from doing this because of

you have to keep track of things

yourself but i am just showing you so

that you know how to avoid these

problems if you happen to be on a

compiler that doesn't protect you from

this so we're going to append goodbye

world to whatever is in dust and down

here if we print this we're going to

have hello world goodbye world printed

out we are going to play with this in a

visual studio code in a minute don't

worry if any of this doesn't make sense

yet here is another example of how we

can join strengths through strcat

we have two strengths and we set them up

with a simple characters like this you

can do this and put in your own now

terminating character this is a legal c

plus plus could and notice that this

array is a dynamic array it's going to

leave on the hip because of this new

operator here we also have a source

array which is also going to leave on

the hip it is 30 characters long so it

is really long and we're going to try

and concatenate stance here but before

we do that we're going to check their

length we're going to print them out and

we are going to concatenate the syntax

is the same you are going to say hdr cat

you're going to specify your destination

and your source you're going to be

copying stuff from and you are going to

store the result in destination here

what this is going to do it's going to

grab whatever is in source and copy it

so it's going to copy the entire thing

here from source and it's going to

append that to whatever we have in

destination starting from the last null

character here so it's going to

overwrite from this null character and

it's going to basically copy everything

and the destination here and if we print

whatever we have in destination here

the phoenix kind of printed out and

you're going to see that this is going

to be the case when we hit visual studio

code in a minute you can also use a

version of the sdr cat version that is

going to allow you to specify

how many characters you want to

concatenate from the source string in

this case we have destination which is

hello and we have source which is there

and down here you see that we do hdr and

cat we save the destination we save the

source and we say how many characters we

want copied from the source here and we

say six characters so we are going to

count from the source we're going to say

one two three four five six we're going

to grab this their string with this

space here and we're going to append

that to the source and that's what we're

going to get in here we're going to say

hello space and there and that's what

we're going to have printed out here if

we print dust we can also copy stuff and

the str cpy function here is going to do

that and here we have an example that is

going to try and drive this home for you

we have a source strength which is c

plus plus is a multi-purpose programming

language okay guest three here is going

to be the same length as the source we

made sure of that in here because we're

going to grab the length of the source

strength please remember that sdrlam is

the null character that's why we are

adding a one here to account for the

noun terminating character here okay

after that we're going to jump down here

and say htr cpy dest 3 and source 3 we

are basically going to be copying from

in destination here that's what we are

doing if we print destination we're

going to see that now it's going to

contain whatever we had in source and

this is how you can use these methods

with which we can specify how many

characters we want copied from the

source here we have a source string

which is hello we have a destination

string which is zest 4 and we are going

to copy stuff we're going to copy from

the source we're going to paste in the

destination and we are just going to

copy five characters what this is going

to do is copy everything from the source

and paste in our destination and it is

going to override whatever we have in

the starting indexes in destination here

so we're going to have a b c d e here

replaced by hello and if we print this

here we're going to have hello f printed

out this is how these things work and if

you wonder how i know how these things

work i just come and read the

documentation here for example htr and

cpy here if we click on it we are going

to get the documentation this is going

to say copies at most count characters

source including the null terminating

character to the character array pointed

to by desk that's what it does we have

the destination we have the source and

we have how many characters we want

copied and they say a few things you

need to be careful about this guy here

one thing that you usually care about is

the return value you see that the return

value is going to be the destination

strength so if you want this pointer you

can use it and you can go down and look

at a few examples here and play with

them to really drive the point home okay

now that you have an idea about how

these guys work we are going to head

over to visual studio code and play with

right away okay here we are in our

working folder the current project is c

string concatenation and copy that's

what we are doing here we're going to

copy our template files and uh jump to

our current project and put them in

place we're going to open this in visual

studio code pretty quick we are going to

include c string because that's what

we're going to be using here we are

going to bring this up a little bit and

we are going to put in our first example

destination and source and you see that

we tried and made sure that they are

large enough to contain however many

characters we want to put in

and they are row arrays stored on the

stack because they are set up like this

and again you can check out the

documentation here if you want to know

how this function works and we are going

to call strcat here to concatenate the

source to our destination here so if we

do this we're going to have world here

concatenated to what we have in hello

here and we're going to have hello world

in place for example if we try and print

this out i'm going to try and do that

after we do the first concatenation here

let's do that that's going to be better

to show you how these things work okay

after the first function here runs we're

going to have source concatenated to

destination here so what we're going to

have is hello world stored in

concatenation here is going to append

goodbye world to whatever we have in

destination here so what we're going to

have printed down is if we print that of

course is hello world and goodbye world

okay we're going to have this written

down let's try and run this and actually

make sure that that's the case and then

we're going to see how this function can

be unsafe for some compilers we're going

to build this with gcc you see that it's

and if we run this we're going to have

hello world hello world goodbye world

printed out this is what we expect and

this function here sdr cat is going to

have whatever you have in source and it

is going to append that to whatever you

have in destination and for this to work

you have to be sure that the destination

is modifiable for example if it was an

array of cost core let's do that and

show you the compiler error we should

get a compiler error because now

destination is not modifiable it is an

array of cost characters and we can't

the destination array is modifiable and

in this case it is okay please note that

some of these functions can be treated

as unsafe by some compilers but i tried

this out on both on gcc and the compiler

from microsoft and they work pretty well

so you can try them out here to prove

that let's go and try and build with the

compiler from microsoft we have it

so we're going to run the task to build

and you're going to see that the world

is going to be good the world finished

successfully and if we go and we're

and run rooster you're going to see that

it is going to do exactly the same thing

but some compilers might give you

warnings or errors if you try to do

something like this and the reason is

you really have to be careful using

these functions because if for example

destination array is not large enough

you may do some crazy things running

over the balance of your array and it

can be really bad for example if we try

and make destination array here for

example a size of three it is possible

to do that and you see that we get a

warning from visual studio code and if

we try and build this with gcc let's try

and remove the garbage we have from

visual studio first now that this is

clean we can uh try and build with gcc

let's do that our compiler we're going

to choose gcc and you're going to see

that it's going to give you an error

it's going to actually protect us from

doing something like this but in some

cases some compilers are not going to

stop you from doing this but any

compiler that really respects itself

it's going to have these safety checks

in and it's going to protect you from

doing something crazy like this okay

this is how you can do concatenation

using hdr cat like we did here let's try

and weld and see that now we are

building fine because i don't like these

red lines here the world is good and we

are all fine now i am going to comment

and we're going to see another example

of how we can concatenate stuff we are

going to go down here let's bring this

and we are going to put in our simple

example exactly the same thing we saw in

character arrays they are dynamic arrays

but we initialize them with characters

like this and we make sure to put in our

terminator we have our source strength

femix king and it's going to have a

and what we're going to do we're going

to take soros and concatenate that to

our destination so what is really going

to happen we are going to overwrite the

null terminator here and we're going to

start pasting in things from source here

so after the concatenation is done what

we are doing here we are concatenating

we are going to have fire lord the

phoenix kang stored in our destination

and notice that we made sure that

large enough to contain our characters

here and if we print it out we're going

to have the thing printed out we can try

and weld with gcc that's going to go

through let's bring this up the bulb is

if you go down here the build is good

we're going to clear and run rooster

okay this is the output here you see

that the destination is eight characters

long if we count one two three four five

six seven eight remember sdrl lan

doesn't count the null character so this

is what we expect eight characters the

source is going to be 17 characters if

you count all this that's what you're

and if we concatenate them now this

in the eyes of hdr land and you see that

we print the destination and it is

exactly what we expect fire lord the

phoenix gang okay we're going to comment

this out i just wanted you to see an

example of this and the one thing i

really want to stress in this example

is that strcat is going to start

overriding whatever is in dust starting

at the last null character okay so this

guy is going to be overridden by the

comma here and we're going to start and

putting stuff and that's what we're

going to see here let's comment this out

because we want to move on and show you

a few other examples okay the next thing

we're going to look at is a new version

of str cat that allows you to specify

from source for example here we have two

strengths destination and source and

here we are basically saying i want to

concatenate six characters from source

and put them at the end of the

destination here and what it's going to

do it's going to grab one two three four

five six it's going to grab this entire

thing and it's going to append that to

hello and we're going to have hello

there stored in the destination and the

return value is going to be a pointer to

destination 2. and how do i know the

return value well i know that from the

documentation if you go in your favorite

stdstr and cat and you're going to see a

link here if you click on it from cpp

reference it's going to give you

everything you need to know about this

function here it's going to append

source to destination and and count

characters are going to be copied so the

third parameter here is going to be how

many characters you want copied and

pasted into our destination

and the return value is going to be dest

okay if we try this out we're going to

see hello there printed out we're going

to print it out directly and we're going

using the destination pointer that is

going to be returned from this guy here

so if we try and build this we're going

to build with gcc the bullet is going to

be good we're going to clear and run

rooster and you're going to see that we

have hello there twice here and this is

we are going to comment this out and we

are going to go down and look at sdr cpi

i should say sdr cpy which is going to

copy stuff from the source and paste

those in the destination and one thing

you should know is that the copy is

going to happen starting from the start

of the destination array here we have

two arrays one is called source three

the other is called destination three

destination 3 is set up on the heap

using the new operator so it is a

dynamic array and you see that we make

sure that it is the same size as the

we are using sdr lan to figure out how

many characters we have in here

and remember that sdr land doesn't

account for the null character so we are

adding one to account for the null

character that's what we are doing here

and after that we are going to do std

str cpy and what that is going to do is

copy stuff from source to destination

character by character so we are

basically going to have this guy pasted

into destination here and if we print

things out we're going to see that

destination contains the same thing as

source here if we built this with gcc

let's do that the build is going to be

and run rooster and you're going to see

that the destination has exactly the

same thing we had in the source and if

you need to copy stuff from arrays sdr

cpui is going to be very helpful

we are going to comment this out because

we still have a few things we want to

so let's comment this out we are going

to go down and see that we can also use

a another version that allows us to

specify how many characters we want

copied from the source okay in this

example here we are using std str and

cpy and this n here means that we can

specify the count of characters we do

the current function is doing here okay

so we are specifying i want five

characters copied from source and i want

those pasted into destination here

that's what we are saying here and the

source is going to contain hello

destination is going to contain the

world and the copy is going to happen

starting at the first index here so

we're going to have hello override

whatever we have in a b c d e because

that's five characters here and the dust

is going to contain hello f if we print

it out let's build this and see if

that's what we're going to get we're

going to build with gcc the build is

we are going to clear and run rooster

and you see that that's exactly what we

okay this is how these methods work

there are many more functions you can

from the c string library and again if

a list of them all you can go through

favorite search engine and search for c

and we can specify cpp reference here

let's try and do that okay we can find a

link to that we can click on that and

it's going to open up and show us many

more functions we can use and if you

need to know about a special function

you can click on it and see what it does

and if you go down you're going to find

even an example of how you can use it

for now we are going to stop here in

this lecture and this is actually going

to be the last lecture we see on c

strings the next one we're going to

start and look at std strength which is

a compound type that makes working with

go ahead and finish up here and meet me

there in this lecture we're going to

start and learn about hdd strength which

is a type that is going to make it super

easy to work with string data we have

seen many ways we can work with

character arrays by now we can use row

rays we can point to them with pointers

we can even allocate arrays on the hip

but all these character arrays had a few

problems that are really a pain in the

neck to deal with on a daily basis

one of those problems was that you had

to keep the size in check you have to

elements you have in the character array

and that was defining the bounds that

you can work in if you go over bounds we

have seen that that can cause crashes of

your program and you don't want that

another problem was that we had 3d to

remember to keep track of the null

character if we don't have it in place

we're going to have problems when our

string is printed out and it's really

annoying to always have to think about

these little details when all you really

want is to store a strand so c plus plus

offers a high level type that we can use

and it is going to hide all these little

details underground and all we have to

do is put in our string and use it and

we can be on our merry way and do

whatever we want to do with string data

in our c plus plus application so that's

what we're going to do we're going to

have a type that is going to wrap on top

of the ugly array computations we have

been doing on character arrays we're

going to call that std string and we're

going to be able to do many of the

things we were doing with c strings but

in a much better way we can concatenate

we can search we can copy we can do all

kinds of crazy things really but it's

going to be in a way that you don't have

to worry about these little details

about array bounds the null character

you're going to just use it for what you

want which is storing character or text

data okay so that's what we're going to

be doing in the next few lectures we're

going to be learning about std string

and how you can use it in your c plus

plus applications and it's going to make

your life a whole lot easier we are

going to stop here in this lecture the

next one we're going to see how you can

declare initialize and use std strength

in your c plus plus application go ahead

and finish up here and meet me there and

this lecture we're going to see how you

can declare and use hdd strength in your

std strength is a type that is going to

wrap on top of arrays and give us a

store string data without having to deal

with the ugly little details like

keeping track of array bound remembering

to keep in check the null character and

things like that to use std strength you

will need to include the string library

and after you do this you can declare

and use your strings just like this here

we have a series of examples just to get

you started on this you declare your

strengths just like you declare any

other time you specify the type on the

left the type is going to be std

strength by the way you'll have to

remember to use std column column like

this and we will have a chance to

explain why in a few chapters ahead but

for now we're just going to think of std

strength as a type so we declare a

string type we call it full name and we

can leave it like this uninitialized and

it is going to be an empty strand we can

also put in our string and initialize

that with a string literal and it is

going to work another way of doing this

is initializing a string with another

string which we are doing down here you

can also set up another string and

initialize it with part of another

string literal so for example message

here is going to be hello and it's only

going to grab five characters from this

string literal this is something you

if it makes sense for whatever

application you are doing here we can

also initialize our strength with

multiple copies of one character and

this is the syntax to do it you say

the name of your variable you say

however many times you want the

character repeated and you say which

character it is just like this we can

also initialize a string with part of

another existing string so for example

here we have saying hello and it is

initialized with part of what we have in

greeting here so we're going to start at

0 1 2 3 4 5 6 on the w here and we're

going to grab five characters so one two

three four five and that's what we're

going to use to initialize this saying

hello here and if we print it out we're

going to see that this is going to be

exactly the case so hopefully you can

see that it is easier you don't have to

use pointers you don't have to use

arrays and the best part is std strength

can grow automatically if you happen to

store in more characters than you

initialized it with in the first place

and that's pretty cool so now we're

going to head over to visual studio code

and play with us so that you can see for

yourself okay here we are in our working

folder the current project is declaring

and using std strength which is what we

are doing here we're going to grab our

template files pretty quick and we're

going to go and store in the files and

we're going to open the folder and we're

going to include the strength library

let's do that okay this is how we do it

and now that we have it included in our

project we can start declaring and using

types in our c plus plus program we are

going to go down and put in the code to

play with this a little bit so you can

declare an empty string like this and

it's not going to have anything inside

you can declare a string and put in a

string literal like we are doing here

and std string knows how to handle this

so it's going to store it inside using a

character array but we don't have to

really worry about that character array

is going to work we're just going to use

std string here we can set up a string

using another string in our initializer

part of a literal to initialize the

this string literal here we're going to

grab part of it and we're going to grab

five characters and use those to

initialize our message std string here

and this is pretty cool we can also use

multiple characters to initialize a

string like this we say however many

copies we want of this character in this

string here and it is going to be

exactly what we want so it's going to be

and we can initialize the string with

part of another string and this is

really cool and it may come in handy in

many applications so for example here

saying hello is going to contain

world here and we are saying that this

is what we want by saying we want to

start at index six in this string here

so if we go zero one two three four five

six this is going to be our character at

index six and from this index we're

going to grab five characters so we're

going to count one two three four five

and that's going to be what's stored in

this string here and if you don't

believe me we can print all these things

out and they are going to be exactly

what we expect and by this you can even

see that we can print std strengths

very conveniently like this and this is

very cool okay so we can try and weld

this with gcc the build is going to go

through so we're going to bring up a

terminal so that we can run this and

we're going to clear and let's see what

run rooster here so we're going to print

the full name the full name is empty

okay so we're not going to see anything

because it is empty we're going to see

planet planet is this thing we have in

here planet where the sky is blue so

this is what we expect we can say

preferred planet and put in the text for

the planet here so we're going to get

and if we have a message and say hello

first characters in this string literal

message is going to say hello which is

what we are saying here let's go down

and look at where the message is going

to be for ease which is what we have

here and we can initialize saying hello

with part of what we have in greeting

and we have targeted this word string

here and it is what we see here and this

is pretty cool the good thing about hdd

string however is that you can

store in more characters than we

initialize this guy with so for example

here we have this message here but we

planet let's go down here and say it

we're going to change std string at run

time so we're going to say planet and

we're going to assign something to it

we're going to put in whatever was in

there first and we're going to paste

that in multiple times let's do three

times i think that's going to be enough

or we can even bring this back so that

we see the entire thing here doesn't

really matter all we want is for this

thing to be larger than it was initially

in a planet here so we're going to

remove these quotes because they are

making things ugly for us and now it's

going to be a valid strength let's wait

for visual studio code to realize that

and it's going to remove these squiggly

lines now we are good std string is

automatically going to take care of the

to make this string grow we don't have

to worry about that and if we print

planet now we're going to see the same

details and taken care of okay this is

really cool and it makes it super easy

text and string data like you see here

so let's build again so that our changes

reflected in our output we're going to

clear and run rooster and we're going to

see that planet is now really large okay

this thing the size of this thing at

runtime and this is something we

couldn't do with arrays so for example

if we go down here and use a row array

to do something like this this code is

going to run but try to think about what

is really happening here we have an

array which contains this text here

and it is pointed to by this cost card

pointer that we have if we try and do an

assignment like this this is really

going to be to make it point to another

character array in memory and this piece

of memory here is basically going to be

wasted because we think we have our

this is not the case with std strength

because std strength when we do

something like this the initial memory

planet here is going to be returned to

the operand system and a new memory is

going to be allocated to contain this

new thing so the waste we're doing here

by just leaving this in memory and not

using it is not being done here so if we

try to print we're going to get the same

output but inside and how our memory is

managed hdd string is better in that the

memory that was used to initialize this

here with array what we really are doing

is just make this planet pointer point

to another string and leaving this to be

wasted in memory this is what we are

doing here and we can avoid that with

in this lecture we're going to learn

about the one definition rule and this

is a rule that says definitions can't

show up more than once in your entire c

plus plus program or in some cases a

definition can show up more than once in

a translation unit we are going to look

at the one definition rule in the

context of freestanding variables

functions classes member functions and

static members in our classes in most

cases a definition can't really show up

more than once in your entire c-plus

plus program but we have exceptions to

this rule and the exception is for

classes a definition for a class can

show up in multiple translation unit and

we need to create objects of those

classes so each translation unit really

needs to see the definition for the

class and we are going to try and make

this super clear with examples once we

hit visual studio code okay so it is

time to head over to visual studio code

and shed some more light on the one

definition rule here we are in our

working folder the current project is

one definition rule we're going to grab

our template files like we always do

we're going to put them in place and

we're going to open this little guy in

visual studio code let's do that i'm

going to drag and drop and we're going

to have our main cpp file here we're

going to clean it up that's what we

and now we want to explore the one

definition rule in the context of

variables so we have a freestanding

and that's going to be the same variable

we had in the last lecture we're going

to initialize this and this is really

good we can use it we can go in main and

use it however we want we can print the

and if we won't run this program it is

going to work but the one definition

rule says we can't have more than one

definition for anything and for this

variable here we have seen that this is

and a definition so we can't have more

than one definition for the weight name

here for example if we try and grab it

and copy and paste it here so we're

going to try and build this program

we're going to see that we have a

problem and the problem is going to say

of double weight and it is not going to

help even if you take this and put that

in another file so let's create another

file to really show you that we're going

to call it some other file that cpp and

we're going to grab our redefinition

and you're going to see that if we try

we're going to get the same problem

we're going to have redefinition so

what is the problem here the compiler

error is a little bit different but it

is going to say multiple definitions of

and it's going to say one is defined in

the main cpp file so this is a linker

error this was caught by the laker

because the redefinition is showing up

in multiple files so the linker was

linking this program and it needed to

see a definition for weight and it had

seen one definition in the main cpp file

and it has seen another definition and

some other file and this is a problem

the linker doesn't know which one to

choose so it's going to throw an error

and you can't really have multiple

definitions for a variable in your c

plus plus program and this is the one

definition rule and the context of

freestanding variables like the weight

here but this is the same in the context

of functions if we go down and put up

our add function here we're going to say

and double b here and we're going to put

the definition below the main cpp file

we can copy this and put this in the

code here i'm going to remove this

little thing we don't want it we're

going to put in our body and we're going

to return a plus b here okay so this is

our function it is working we can take

out what we had here because it has

served its purpose you can say double

result and we're going to add up 10 and

20 like we did in the last lecture

no problem and we can try and print out

if we build and run this program it is

going to work without a problem because

we only have one definition for the add

what is the problem here we have weight

defined multiple times we're going to

comment out one the definition for

and we're going to build again

now the build is good and we can run

kill our terminal here and bring up

another one and run rooster you're going

to see that the result is 30 and the

program is working just fine but if we

set up another definition for add even

if we put this in the same file

we're going to get a problem because we

are violating the one definition rule

you're going to see the problem here

we're going to see redefinition

redefinition of the add function this is

not allowed your program is not going to

compile we see the compiler error here

even if you put the definition in

another file that's not going to help

we're going to take this and put this in

and try to compile the program

we're going to get a linker error and it

is going to say multiple definition of

the add function and this is not allowed

this is a linker error in this time if

we comment out one definition let's do

that we're going to comment out the one

in the main function this is going to

work and we want to be violating the one

definition rule so this is good the

and run rooster we're going to see our

result here so the one definition rule

says you can't have multiple definitions

freestanding variables or even functions

and reserve that if you do that you're

going to get a compiler error let's look

at this in the context of classes we're

going to do a class we're going to say

struct and we're going to call this

mostly we're going to call this point

and we're going to put in a few member

variables one is going to be mx the

and this is going to be our definition

but what you're going to see

is that it is possible to have multiple

definitions for classes for example if

have a copy of this in another file

we're going to do that we're going to

and we're going to try and build this

program you're going to see that it is

working we have multiple definitions of

these guys we can go in main for example

and we can up weld and see that the

program is going to work okay so if you

go in here for example and try to print

p1 and the print x we're going to do

that we're going to say p1 mx we're

going to be able to use this because

this is a struct the member variables

are public by default we can do this

p1y my let's do that and we can say

stdndl what is the problem here we need

to put our output stream operator

i think now the compiler is going to be

we're going to see that if we run the

program we're going to see our things

here and we have some junk values inside

because these things are not initialized

but if we initialize them to zero using

the braced initialization here

and we should see zero inside so let's

clear and run rooster now we have 0 in x

and y for our object here this is

working fine and we have multiple

definitions for our class but the

definitions can't show up in a single

translation unit for example if we took

and brought that back in main and put

our structure here if we try to weld the

compiler is going to complain because

now we have multiple definitions for the

same class in the same translation unit

we can have multiple definitions but the

definitions have to show up in different

translation units and that's what i want

redefinition of our point struct and it

is not good it is going to violate the

one definition rule okay now that you

have seen this we also want to see this

that also has some static member

variables we're going to take this out

because we have already seen this and

we're going to bring in our person class

like we used in the last lecture we're

going to add in a new header file it's

what did we do is this folder let's

remove this we didn't want a folder

we're going to delete this folder we

and we're going to just add a file

that's all file here and we're going to

put in the content the content is going

to be our personal class let's close

this so that you can see more of this

class here okay so we have our person

class here we have our include card we

have our person class definition we have

a constructor and we have a printer

phone function we have our member

variables and down below here you see

that we have a static variable which is

person account we need to put in the

definition for these guys so let's go

down and do that we're going to put in

constructor we're going to go on top

here and include our person header file

and we're going to put in place our

constructor we can go down and do that

we can say person and say person

that's going to be our constructor we're

going to go back to the class and grab

the parameters because i don't want to

so let's do that we're going to put them

we are going to put in our initializer

list i think we should also delete a

parenthesis here we're going to go down

and put in our initializer list we're

going to say full name we're going to

initialize this with name param

and we're going to also put in our age

and we're going to initialize this with

edge param the parameter we have from

the function and this is going to be all

inside the body we're going to implement

the static variable we're going to say

increment person count okay now select

that here and this is going to be good

we also need to initialize our static

variables so we're going to say ends

person person account let's do person

account and we're going to initialize

this to maybe eight like we did in the

last lecture and this should be all we

need here so if we build and run this

program i think it's going to run

let's select the main function here

and what problem do we have here let's

build and see we're going to let the

we're going to see that the world is

good and we can create person objects

and really use them in our program so

let's come down here and delete whatever

we had we're going to include the person

and we're going to go down here and

create a person object we're going to

p1 and we're going to specify the name

and we're going to say that they are

and we can preach information about this

person we can say person principle and

if we try to build this program let's

the world is going to be good as you see

and run rooster we're going to see jon

35 years old so this is working just

multiple definitions for the same class

in the same translation unit here for

example if we come in the main function

notice we are including a person so this

is bringing in the definition for a

person we have in our person.h here if

we also try to declare another class

even if we don't put anything in the

compiler is going to complain because we

have two definitions for the same name

which is person here if we try to build

i think we are going to get a compiler

error saying that we have a definition

you see we have a redefinition of person

so this is not allowed we can't really

do this but notice that this person

class is included both in some other

file which is a separate translation

unit and main we have it included here

so it is really in a separate

translation unit we have the definition

for the class in separate translation

units and that's not a problem but if

you try and put the same definition

multiple times in a single translation

unit you're going to get a problem and

you need to be aware of that what i want

you to see right here is that you can't

also have multiple definitions

for your static variables and the member

functions of your class for example if

and also put that in our main function

we can do that why not we're going to

come in our main function here and we're

going to put the same definitions here

now we're going to have a problem

because the linker is going to see two

definitions for the static variable and

the constructor for a person here and

this is going to be a problem you can't

really do that if we build we're going

a problem we're going to see

we have multiple definitions for the

constructor and we have multiple

definitions for person account and this

is not allowed you can't really do that

you can either remove the one from some

other file.cpp for example if we comment

let's do that we can come on top here

and comment this out and try to build

the program now the program is going to

work because we have one definition for

these guys you see the world is good we

can even run the program to show you

that it works or we can remove the one

in the main cpp file and we can leave

this alive so let's go back in the cpp

file the main cpp file i should say and

remove this and if we work we're going

to see that this is going to work and

compliant with what the c plus plus

standard expects us to do in our c plus

plus programs if we're around we're

going to see that this is going to work

and this is really cool this is really

all i wanted you to see in this lecture

the one definition rule which says that

you can't have multiple definitions for

the same name in your entire c plus plus

program but for classes we can violate

this rule a little bit and make the same

definition show up in multiple

translation units we are going to stop

here in this lecture in the next one

we're going to learn about linkage

go ahead and finish up here and make me

in this lecture we're going to learn

about functions a function is a reusable

piece of code that you can use multiple

times to do different things it can take

input and once it has input it can do

some processing and when the processing

is done the function can optionally give

you a result you can think of a function

as a machine which can take input and

give you some output when you give input

to the machine the machine is going to

do some processing and then it's going

to give you the output and the output is

going to be dependent on the input that

you gave to the machine this is really

how a function works in c plus plus and

once you have the machine set up you can

really reuse it however many times you

want let's look at how a function looks

in c plus plus the syntax is this you

first specify the return type which may

be and double or whatever after that

you're going to specify the function

and after that you're going to have a

pair of parentheses inside this

parenthesis you're going to have your

parameters which is going to be a comma

separated list of things you pass to the

function and after all these parameters

you're going to have a pair of curly

braces and inside those curly braces

we're going to have the body of the

function we're going to be doing our

processing in the body and when the

processing is done we can get the result

of the function through this return

mechanism here so if we want to get

something out of the function we have to

return that thing and it is going to be

visible to whoever used this function

here is a simple example of a function

with no input and output the syntax is

going to be this void means that this

function is not going to return anything

and you notice that our pair of

parentheses is empty because we have no

input in this function we have our curly

braces and inside these curly braces is

going to be the body of this function

it's going to do some processing and

when processing is done we return out of

this function now remember that i said

that this function doesn't return

anything because it is of void type here

but we can return and i'm going to show

you the exact syntax of how you can do

that okay so we can have many functions

in c plus plus but each function has to

be unique otherwise you're going to have

problems in your c plus plus programs a

function is going to be unique based on

its signature and the signature is

plus the function parameters if we go

back to our example here and try to

figure out the signature of this

function it's going to be function name

and plus the parameters and you see that

we have no parameters in here so this

signature is going to uniquely identify

this function in our c plus plus program

if we set up another function that has

this same function name and doesn't take

any parameter we're going to have

problems even if we happen to have a

different return value for the function

and don't worry if this is not making

sense yet we will see a lot of examples

and i am sure by the time we are done

with this lecture you will be a master

at using functions okay now that we have

seen how we can declare or define a

function in c plus plus let's see how we

and when you call a function in most

cases you will want to get something out

of that function so suppose here result

var is a variable that is going to catch

and we're going to call the function

with the syntax like this we're going to

say the function name we're going to put

our pair of parentheses here and we are

going to pass in the arguments or of the

values of our parameters this is the

syntax it is going to call the function

and the result of the function is going

to be assigned to this result var

variable of hours here is how you can

call a function that doesn't take any

parameter the parameter list is

basically going to be empty and now

we're going to look at a few examples of

how you can really declare functions in

your c plus plus program for example

here we have a function called into bar

it doesn't return anything so we can't

catch the result of this function and

it's going to have one input in the form

of an integer so the parameter is called

h here it's an integer and inside the

function we are going to test if

somebody is old enough to enter a bar so

we do a test to see if the age is

greater than 18 if it is we're going to

tell them please proceed f the h is not

greater than 18 we're going to tell them

you cannot enter this is an example of a

function you can set up in your c plus

plus programs here is another function

that is going to compute the maximum

between two numbers it is going to give

us a result so the return value is an

integer here the function name is max

and we're going to put in our list of

parameters and again these are the

parameters when you are defining your

this comma separated list of things we

have in this parenthesis are called

parameters and when you call the

function the values that you pass in the

places of these parameters are called

arguments so these are a few terms that

can really throw you off and i just want

you to be super clear about these things

once we have the signature of the

function set up we jump in the body and

we do whatever we want this function to

do so we're going to say if a is greater

than b then a must be the maximum we're

going to send it that back to whoever

called this function or in other words

and if a is not greater than b then b

must be the maximum and we're going to

return it that's what we're saying here

here is another example of a function

that doesn't have any output and doesn't

take any input it doesn't return

anything because the return type is void

and it doesn't take any input because

the parameter list here is empty and the

body of the function we're just going to

greet somebody and tell them hello there

and we're going to return out of the

function notice that for avoid function

we can either omit the return statement

here or we can just put it in like this

say return and the semicolon and

whatever c plus plus compiler you are

using is going to accept this as valid c

here is another example of a function

that returns something but doesn't take

any input the return value is going to

be an integer but we don't need to pass

something to this function when we call

it it's just going to give us output we

can call it and get our lucky number and

use that however we want in our c plus

plus application i think we have seen a

lot of examples of how we can set up

functions now let's see how we can call

these functions here is a simple c plus

plus program in the main function we

just set up a few variables a value b

value a and b here and we use those

variables to call functions remember we

set up an inter bar function the

function looked like this and it was

testing to see if somebody's age was

greater than 18. if the age is greater

than 18 they are going to enter the bar

if the edge is not greater than 18 we

won't let them end the function takes

input but it doesn't return anything so

we can call this function like we do

and you notice that we're not catching

something out of this function we're

just going to call it and we're going to

give it input which is 22 here and the

function is going to do its thing so

it's going to let us in because our age

is greater than 18. down here you see we

are calling the max function here we are

giving it two inputs a value and b value

and it's going to return something and

the return value of this function is

going to be used to initialize this

maximum number variable here this is

what we are doing if we go down we see

that we can call the maximum function

directly and use its return value in an

sddc out statement here and this is

going to print out the maximum between a

and down here you see we have the

function say hello which is going to

just greet somebody and not return

anything here is another example of how

you can call the lucky number you say

lucky number you pass a pair of

and this is going to return the lucky

number and print it out in this htdc out

statement here down here we set up a few

variables a and b and we are going to

use them to call the maximum functions

you see we call max a b or we can even

pass in number literals like we are

one thing i want you to be careful about

is implicit conversions that might

happen when you are calling you

suppose we have a minimum function like

we see here which is going to be taking

in integer parameters but here we are

calling the function with f and g

which happen to be of double type like

we see on top here so what is going to

happen is the compiler is going to

notice that what you are passing in is

not really what the function takes but

the compiler knows that it can insert a

transformation from double to integer

and it is going to do that without your

involvement so be really careful about

implicit conversions and make sure they

are working to your advantage otherwise

you're going to have really hard to

debug problems in your c plus plus

one other thing i want you to be aware

of is that if we have a function set up

like this this function is going to be

taking parameters as copies so if you

have two variables for example c and d

and you call this function with those

two variables you're not going to be

manipulating those two variables what

you will be working with inside the body

of this function are going to be copies

of the parameters that you passed in

here so if for example you happen to

increment either of the parameters for

example here we increment a and we

the changes we make here inside the body

of the function are just going to be

affecting copies we have inside the

function here and these copies are going

to die the moment we hit the end of this

function here this is something i want

you to be aware of and we will play with

that in more detail when we hit visual

studio code in a minute here is a simple

example of how you can call that

function we have two variables h and i

and we are going to print them out after

that we're going to call the function

we're going to store the result back in

mult results but the important thing is

that we call the function here with h

remember in the body of the function we

are incrementing h and i as arguments

but the changes we do inside of the body

of the function are not going to be

visible when the function returns if we

print h and i here we're just going to

see the same thing we saw before we call

i realize this is a lot of information

to take in now we are going to head over

to visual studio code and actually play

okay here we are in our working

directory the chapter is on functions

the current lecture is first hand on

functions we are going to grab our

template files like we always do we're

and we are going to open this in visual

studio code let's open the folder

and we are going to go in the correct

and choose first hand on functions here

this is what we want to open and we are

going to open our main cpp file and

and the first thing we want to do is to

set up a function that takes a single

parameter and doesn't give back any

result so the function is going to be

interbore we have seen that the function

is not going to return anything so it's

going to be void its return type is

going to be void the name of the

function is going to be interbar and

what we want to pass in here is a

variable to represent the age of

somebody and we know that the age can

really not be negative so it is

advised to at least use an unsigned

integer type so we're going to use

unsigned end and the parameter name is

once we have our parameter list we're

going to put in the function body and

remember the function body is going to

now this is a valid c plus plus function

it's not going to return anything it's

going to take a single parameter whose

type is unsigned and its name is

interbar we can get inside the function

and actually do whatever it is we want

to do so once we go in we're going to

test and see if the age is greater than

18 do something if the age is not

greater than 18 we're going to do

something else let's do that we're going

age is greater than 18 we're going to

tell them the age and tell them that

they can actually go in this is logical

and we're going to say else and in the

we're going to say something else

we're going to tell them sorry you are

too young for this and we are going to

get out of this block here and this is

really our function again let's try to

analyze the syntax here we have the

return type this is required in c plus

plus if you don't put it in you're going

to get a compiler error because you

can't have a function without a return

type in c plus plus you notice that we

have our squiggly lines here visual

studio code is not happy so we're going

to tell it the return type we're going

to save the function name after that

and after the function name we're going

to pass the parameters we can have any

number of parameters or inputs to the

function but in this case we just have

one because it is enough for our

purposes after that we have the body and

inside the body we do whatever it is we

want to do in this function here because

this function returns void we don't

really need to explicitly return from

this function here but this is an

exception only for functions that return

void for other return types you will

have to put in the return statement but

even for void functions you can put the

return statement if you want and you can

and you're going to put a semicolon

after this this is also valid c plus

plus syntax okay now we have declared

the function it is a valid c plus plus

functions let's try and call it we're

going to go down in main because that's

where we want to be calling our

functions for now and we are going to

say interbar we're going to call the

function and you use the function name

to call it and you're going to put in a

pair of parentheses and pass an argument

to the function again what you pass to

the function when you call it it's

called an argument but what you pass

through the function when you are

defining it like we did here that's a

okay so function parameters when

declaring functions and when you are

calling the function what you pass are

arguments and now we need to pass in

some age to this function and let's say

22 and if we do that this is going to be

notice that we have this squiggly line

it is because we forgot a semicolon here

c plus plus requires to have a semicolon

after each statement and now we have a

valid c plus program that is declaring a

function and calling a function down

here in main we can try to build it

let's use gcc to do that the world is

going to be good you see world finished

successfully and we can bring up a

terminal and actually try to run this

function here let's clear and run

rooster because our program is going to

be called rooster like we have been

doing all along and at the output is

please proceed notice that we have this

function defined once but we can call it

multiple times so for example if you go

and we try and build again let's build

the builder is going to be good we can

clear and run rooster now it's going to

say you are 15 please proceed why is

what are we really doing here uh if age

is greater than 10 we say 10 here we

should say 18. sorry for this we're

and now it should behave accordingly so

you are 22 please proceed you are too

young for this no offense because the

age is 15 here you can keep calling this

function and you're going to see things

printing out you can even call this

function in the loop i can't really

resist so let's do that we're going to

i and say start from 0 for example or 1

and we are going to say while i is less

20. we're going to increment uh you

already know how to use loops so we're

going to be using this as an example

comment out all these guys in front

because we don't want them to print

and what we're going to do is call the

function with whatever iteration we are

notice that we have a size t here and

the function is going to be taken

an unsigned integer so we're going to

have implicit conversions from size t

to end or if we really want this to not

cause any problems we can change the

type of our parameter to be size t this

is also valid c plus plus code let's say

watch what is going to happen this is

from 1 all the way to 19 and it's going

to be calling this function with

whatever iteration we might be at so

it's going to look from 1 all the way to

tell us we are too young for this but

for 19 it's going to let us in because

we will be old enough to enter a bar

let's try this i think it's going to be

fun we're going to weld with gcc

and run rooster ah sorry you're too

young for this you too young with us and

that once we hit 19 it's going to tell

us we are young enough to enter a bar

and we're going to go and and have as

much fun as we want so this is really

how you can declare a function remember

a function is uniquely identified by its

signature and the signature is really

the name of the function and the

parameters that you have in here okay

once you have the function declared

you're going to do whatever you want in

the body you are going to optionally

return something from the function and

once the function is declared or set up

you can go in main and call it and do

whatever it is you want with it okay now

i think we are mature enough to try out

a few other functions let's go down and

put in another function which is going

to compute the maximum of two numbers

the signature of this function is going

to be its name here and the parameters

notice that we are taking two parameters

because we want to be computing the

maximum between two numbers and this

function is going to return something we

want to get the maximum out of the

function and use it to do something else

so this is the declaration of the

function once we hit the body of the

function we are going to compute the

maximum we're going to say if a is

greater than b then a must be our

maximum so we're going to return that

and if a is not greater than b then b

must be the maximum we're going to

return b as our maximum here this is

what the function is doing we can go in

main and call it let's go down and

comment this out because we don't want

noise output from these guys so calling

interbore that's what we were doing now

we are calling max so we're going to go

down and set up a variable call it

result why not and we're going to

compute the maximum between 10 and 20

why not okay so let's see what we get

and we're going to print the maximum

max as resort okay now if we build this

program and run it try to guess what

we're going to get we're going to call

and what we pass in here are arguments

again we are not passing parameters here

we are going to pass in 10 and 20 as our

arguments and when we call the function

control is going to jump to the body of

the function and we are going to fall

inside here the arguments we're going to

pass in are just going to be copied in

the function and we will have them

through these names a and b so we're

going to test and see if the first

parameter is greater than the second in

this case the first parameter is not

greater than the second because the

first one is 10 the second is a 20.

let's go down and see that and the test

here is going to fail and we're going to

run whatever is in the else block here

and we are going to return b as our

b is going to basically be the result of

and that result is going to be assigned

to our research variable and we're going

to print it out with this sddc out

statement here so let's try and build

this we're going to build with gcc again

the world is going to be good we're

going to clear and run rooster you see

that maximum is 20. if we try and change

this for example make the first

let's see what maximum we get

going to clear and run rooster we're

going to say that maximum is 100 and

again you can call this function however

many times you want for example we can

call it again and say result equals

max using two variables that we have

and go on top and declare these two

variables why not we're going to say and

x and we're going to put in it 22

and we're going to say end y and put in

and now if we print the result we're

going to get 44 because that's the

maximum that was assigned back to our

research variable here let's weld again

we're going to run the task to build

you can clear and run rooster you see

max is 44 and this is really how you can

declare and use a maximum function like

we're going to comment this out because

we have a few more functions we want to

try out let's go on top and put in

another function and again notice that

before the main function here this is a

requirement of a c plus plus compiler

because before you use the function the

function must be declared somewhere so

we need to go before the main function

and declare our functions here the

function we're going to do now is say

hello here it's not going to take any

input and it's not going to give us any

output it's just going to say hello and

die off we can go down and call it this

is going to be super easy calling hello

and we're going to call it say hello see

that even visual studio code knows about

this function we can call it like this

it's going to be activated so we're

going to hit the body of the function

we're going to say hello there and the

function is going to return or die off

please know that you could omit this

return statement for functions that

return void so if we comment this guy

out the function is going to work

equally well you can use this however

you want now we're just going to build

with gcc and see this function run

the build is good we're going to run

rooster and it is saying hello there

let's go down and look at another

the next function is going to be lucky

number it's not going to take any input

but it is going to give us an output in

the form of an integer so we can call it

let's go down and comment out saying

hello here and say that we want to call

and we can go down and set up a variable

let's do that we're going to say int

are going to brace initialize this guy

so it's going to be initialized to zero

and we're going to say result

equals lucky number and we're going to

take the result returned by our lucky

number function and assign that to the

result variable and we can print it out

if we want so we can say sddc out and

and we're going to put that out here say

and if we build and run this program

we're going to get this guy printed out

we should see a 99 because that's what

we are returning from our function here

and resort is 99 as you see in the

output here so this is really how you

your functions a function has a unique

signature so for example into bar here

if you go down mats has its own name and

the parameters that it takes in if you

go down say hello and lucky number are

different in their own ways if you try

and set up another function that has the

same signature as max here your compiler

is going to freak out let's try and do

that we're going to set up another

function it's going to have a void

return type we're going to call it max

because we want to match this signature

and we're going to give it two

and we can do whatever we want in this

function notice that we have a squiggly

line if we open our problems tab here

you're going to see that visual studio

code has a few problems with this

because we are setting up a function

with the same signature twice let's try

and different make this a net and see

what we get right now we don't seem to

have a problem but if we get to run this

program we're going to have problems

let's go down and actually activate the

code to call the max function to really

because you need to know so we're going

to comment out calling lucky number and

we want to call max we're going to

and we are going to build this with gcc

notice what we're going to see uh-huh we

have problems here we have a compiler

error saying re definition of int max

one might think what if i name my

parameters differently here for example

using different names like this is not

going to solve your troubles because if

we try and uh bold again we're going to

get the same compiler error this is not

going to change your thing we don't have

enough tools to really understand this

problem but know that you can't have two

with the exact same signature in a

single c plus plus program and we're

going to learn more about this later but

note that the signature of a function

must be unique to it throughout your

entire c-plus program if you remember

this simple rule you're not going to

have many problems so let's try and weld

again to make sure we have no more

the bolt is good and we can run the

program to see our maximum printed out

rooster and max is 44 it is exactly what

the last thing i want to do in this

lecture is make it super clear in your

mind that what we pass to functions we

are copies so let's go on top and set up

a simple function the function is going

to increment and multiply it returns a

double type the name of the function is

increment and multiply and it is going

to take two parameters and a double a

once we hit the body of the function

we're going to increment a and b

the arguments that were passed to the

function and we're going to multiply

them and we're going to store the result

of that in a reserved variable the

result variable is what we're going to

return to the function and whoever

called this function is going to use

that to do whatever they want what we

really want to see is that the changes

we do inside the function are not going

to be visible to the arguments that we

pass to this function here to really

make this super clear let's go down in

main and set up a few variables we're

going to have a double h and the double

i the values are going to be three and

four we're going to print them out and

we're going to call our increment

multiply function notice that we pass h

to the function and the result of the

function is going to be stored in uh the

anc mult resort variable here but the

return value is really not important

is if the changes we do to the arguments

are going to be visible on the outside

of the function here so remember we have

h and i here we pass them to the

function once we hit the inside of the

we're going to increment a and b

and we are going to return from the

if a which was a 3 and b which was a 4

have been incremented to 4 and 5. that's

what we want to see so we're going to

boil this and run this so let's use gcc

to do that the bulk is going to be good

and notice what we have here let's go

down and look at the variables again

we set up h to contain a 3 so before we

okay so that's what we're going to print

here once we hit the inside of the

we are going to say what we have inside

the function before we do the operation

before the increment again a and b are

four so these are copies we have inside

do the increment and after we have the

increment a and b are going to be four

but once we hit the outside of the

with this guy here we're going to see

we didn't really affect h and i when we

did this increment here what we affected

are copies that were passed to a and b

and this is something you need to know

because some people will think that

h and i in my argument list here i can

manipulate h and i what you are

manipulating are copies that were made

by the compiler to pass the arguments to

the function here this is something you

need to keep in mind and we will learn

more about this but i wanted you to

learn this firsthand and this is really

all we set out to do in this lecture i

hope you have a better understanding of

what a function is and what you can do

with it in c plus plus we are going to

stop here in this lecture in the next

one we're going to learn a little more

about function declarations and function

go ahead and finish up here and meet me

there in this lecture we're going to

learn about function declarations and

function definitions the motivation for

the topic we're going to be talking

about here is that sometimes you really

want to separate a function header from

its implementation because you don't

want to expose all the details about how

you do stuff let's look at the simple

example in the last lecture we declared

a max function which was computing the

maximum between two numbers the output

was an integer so that's what we

returned the name of the function was

max and we had two parameters into a and

and b but what we did in the last

lecture was crop the entire function

in front of main but sometimes people

don't want to really see the details of

how you do stuff they just want to know

a summary of what your function does

what we can get out of the function and

what we need to give to the function for

it to do its job and that's what we're

going to see in this lecture if you look

here we have the function header in

front of the main function and the

function header is made up of its return

type the name of the function and the

list of the parameters and after that

we're going to put a semicolon this is

called a function header or a prototype

and when we do that the compiler is

going to be happy and it's going to work

with us to compile our program but when

we get to link our program to really put

it together and make one binary the

definition of the function is going to

be needed and if you look after main

here what we have is a function

definition if you look closely you see

that it is exactly the same thing we had

in the last lecture we have our header

information we don't have a semicolon

after our parameter list but we have a

pair of curly braces and inside these

curly braces we have the body of our

it is really easy to look at this

program because we don't have to look at

all these details about how this

first-hand information on how we can use

this function and that is what most

people are going to be interested in

about your function they want to really

want to go in and see how you do stuff

they will want to use your function to

get the output and use it to do whatever

it is they want to do if you look here

in the body of the main function we have

two variables a and b and we use them to

call the maximum function we can also

set up a minimum function which works in

the similar way and we call another

function called increment which is going

to increment and multiply whatever

arguments we pass to this function so

the main idea here is that we can split

our function in two parts one is going

to be the function header which is

really going to be the function

declaration and the other is going to be

the function body with all the details

about how the function works and that's

going to be our function definition and

once we have these two things in place

we can call the function in our main

function and do whatever we want with

that okay now it should be super clear

that we can separate our function in two

parts declaration and definition and

sometimes the declaration part is also

called a prototype that's a prototype of

a function and it is made up of the

together with the function name together

with the parameters and after that

you're going to add a semicolon to make

it valid c plus syntax and another thing

you should know is that the prototype

needs to come before wherever it is

called if you're trying to call a

function before its prototype is seen in

your c plus plus program you're going to

get a compiler error and now you might

be asking but why did our programs in

the last lecture work we didn't split

things up and our program was working

if you put a function definition in

front of the main function that function

definition is also going to double as a

function declaration that's why the code

in the last lecture worked okay now that

you have an idea about what a function

declaration and the function definition

is let's head over to visual studio code

and play with us okay here we are in our

working folder the current project is

function declarations and definitions we

are going to grab our templates files

we're going to put them in place

and we are going to open this guy in

visual studio code let's do that

and we are going to open our main cpp

file clean it up a little bit and let's

close this pane so that we have some

breathing space the first thing we're

going to do is set up a maximum function

you already know how to do that we're

going to specify the return type

we are going to specify the function

name and the parameters we're going to

take in it a and into b and we're going

to go in and do whatever we need to

compute the maximum between these two

guys we're going to say if a is greater

a must be the maximum so we're going to

okay this is the function and it is

really simple we can go down in main and

x and i put in a five for example

y and put in a two or a three put in

and then we're going to set up the

which is going to catch the maximum i

think we can do that and what we're

going to assign to this is whatever is

returned from our function call so we're

going to call this function with x and y

so we're going to be computing the

5 and 2 here the maximum is going to be

stored in this result variable and we're

going to print it out so we're going to

see out and i'm going to say max

as result this is going to do

okay let's try and build this and make

this is nothing new so far it is

everything we have done in the last

now the world is good we can clear and

run rooster we're going to get the

maximum as a five here and if we try to

change this things for example make y 12

and we are going to clear these thanks

and run rooster we should get max equals

this is all fine and dandy but sometimes

we don't really want to have the details

about how our function works shown in

front of the main function here and we

can split our function in two parts a

declaration and a definition the

declaration is really going to be the

header part of the function and that's

going to be the return value the name of

the function and the parameter list but

to make it a valid declaration we have

to put a semicolon after this so this is

sometimes it is also called a prototype

and please make sure you understand the

difference between a prototype and a

signature in the last lecture we saw

that the signature was only made of the

name of the function and the parameter

list but the return value was not part

of the function signature but the

prototype includes all these guys so

okay so now that we have our function

declaration setup we need to put in

a function definition because if you try

to compile this program and link it

you are going to get problems let's try

and do that before we put in the

we can weld with gcc we are learning so

have to fear breaking things a little

let's clear and try to build with gcc

and you're going to see ah we have a

problem here and what kind of problem we

have the c plus plus compiler is going

to compile this program but when we hit

i realize i haven't really talked about

this in more detail but we will do in

this lecture but the main problem here

is that we don't have the definition of

this function in place and the compiler

is going to search for it and not find

it and you see that it is saying

okay so it has seen the declaration of

but it doesn't know how the function

does its job because we don't have a

function body in here so to really make

this code work exactly as we want we

need to put in a definition and the

definition can show up anywhere in your

c plus plus program in this case we're

after the main function and the

what we have been using so far as our

function definition in the last lecture

but notice that it has the body

information and now when the compiler

tries to compile this program it will

know how the maximum function is

computing its maximum because we have

all that information in here so let's

say that this is our function definition

and shows up after main in this case and

we can try and build this and see if the

work is good now you see the world is

and if we try to run it we're going to

get our maximum exactly like we did when

the declaration and the definition

cramped up before main here but

hopefully now you can see that our

program is much cleaner because when you

look at this you know that we have a

function called max it's going to take

two parameters it's going to return

something and it is called mats so it

must be computing the maximum of these

two guys but we don't really care how

this function does its job how it

computes the maximum here and this is

the main message here we can split a

function in two parts a declaration and

a definition okay just to play around we

can also set up a minimum function

before we do that let's set up its

definition down here we're just going to

copy the maximum and adapt it

we're going to put a copy of that guy

here we're going to call it men

it's going to take two parameters it's

going to return an end but what we test

for is if a is less than b if a is less

if a is not less than b then b must be

our minimum and we can put the

declaration of this function on top here

so let's go there and say men

and now we can change the call here to

say mean and it is going to compute the

minimum why not let's do that we're

going to say min here and we're going to

grab whatever is the minimum between x

and y here and that's what we're going

to have in this result variable here

let's do that we're going to try and use

so we're going to clear and run rooster

now the minimum is five we are calling

in the last lecture we also set up a

function to increment and multiply let's

but split that into a declaration and

the definition just to practice a little

more we're going to call this and

malt and it's going to take a and b in

and inside and we're not going to put

the body on top here we're going to put

the body down with the other definitions

that we have for all these other

functions for max and mean here so we're

going to put in our body it's really

simple so we're going to put a body

and we're going to multiply that with an

and we're going to return that i think

this is going to be valid c plus plus

syntax and if we try to call this

function in main let's do that say in

mult and we're going to pass an x and y

the program is going to just work fine

we're going to grab the result and store

in our variable let's do that

and we're going to say result here this

and if we build and run this program

we're going to see the output here let's

the results is going to be 78 because if

we increment a 5 it becomes a 6.

if we increment y we're going to get 13

13 times 6 should be 78 let's be sure

we're going to bring up the calculator

let's do that so that you know that i am

not making these things up 78. so our

program is really working like it should

and this is the main message here we can

really split up functions into a

and a definition and that's going to

make our programs much easier to work

one thing you should know is that the

names of the variables aren't really

important in function declarations like

so for example we can take out the a and

or we can take out all the variable

names in our function declarations let's

and you might think is this program

going to compile well i hate to break it

to you but it is going to compile so

you're going to see that the both is

good so the function header or

declaration doesn't really care about

in the definitions we care about these

variable names because we are going to

be using them in the bodies but if you

want you can leave them out in your

function declarations but i like to keep

them in place because i like my

functions to be self-documented if

somebody looks at this they will know

the variable name here but if you really

want you can leave the variable names

out and it is going to work pretty well

this is really always enough to do in

this lecture i hope you found it

interesting we are going to stop here in

this lecture in the next one we are

going to see how we can split our

programs in multiple files now that we

know how to split into declaration and

go ahead and finish up here and meet me

in this lecture we're going to revisit

our c plus plus program compilation

model along the way we are also going to

see how we can work with functions

if you remember our compilation model

looked something like this you have seen

this slide a lot of times by now what it

describes is what happens when we

compile our program the moment we run

the compilation command our c plus

program which lives in the main cpp file

by now is going to be passed through the

compiler the compiler is going to

process it and it is going to come up

with a binary executable that is mostly

called rooster in this course and when

we execute this rooster file or binary

file we're going to get the program to

run the program is going to be executed

instruction by instruction when it is

loaded by the operating system and we

are mostly going to see the output of

that program on the terminal in this

course this is the compilation model we

know but now what we want to do is zoom

in on this compilation part here and see

what really happens under the hood

we are going to suppose that we have a

program which is made of a lot of source

files as we have here on the left

suppose we have two three or five source

files unlike what we have so far which

is one file the main cpp file when you

compile such a program you're going to

pre-processing and what this is going to

it's going to look for your include

and it is going to take whatever file

you are including and it is going to

paste that in place so for example here

you see we have an include io stream

when the pre-processing stage is run

this includes statement is going to be

replaced with whatever we have in this

io stream file here so this is going to

be wiped out and we're going to put in

the content that we have in io stream in

this exact place where we have the

include statement i hope this is clear

so when we go through preprocessing

a version of our source files

with the included parts put in our

source files we're basically going to go

copy everything in that file that we

include and we're going to paste inside

our new files here that we're going to

be referring to as translation units by

now these are translation units in a c

once you have this translation unit then

you're going to compile them they are

going to go through the compiler the

compiler is going to generate what we

call an object file and this is a binary

representation of the content you have

in your translation unit so each

translation unit is going to generate

one object file and for example if you

had 20 translation units in your program

you're going to have 20 object files

once we have object files they are going

to be processed by what we call the

and the linker is going to stitch them

together and have one single binary file

out of all these object files so we're

going to have something like this and

this is basically going to be our binary

that we can run on our target operating

system so by now you see that our

compilation model has expanded to

pre-processing compilation and linking

now you might be asking why am i showing

you this now well it is going to matter

because we're going to split to a

program across multiple files some of

those files are going to matter on the

compilation phase and some of those

files are going to matter on the linking

stage so we really need to make a clear

distinction between the compilation and

linking here okay this should be a more

complete compilation model to go by for

now now that we know about this

compilation model we can look at how we

can split our program across multiple

files suppose we have three functions

one we can use to get the maximum of two

numbers called max a function called men

we can use to get the minimum between

two numbers and a function we can use to

increment and multiply like we have seen

in the last lecture now the two

functions maths and men are going to

live in their own file and that file is

going to be split in two files we're

going to have a header file and a cpp

file which is going to contain the

implementation in the header what we're

going to have is just a prototype and we

are going to set up our code in a way

that our anchor mult function here is

going to live in zone file we're going

to split that in two files so we're

going to have a header file called

which is going to contain the

implementation of this function here

when we hit the main file what we're

going to do is nothing special we're

just going to include the headers and we

are going to use these functions like we

have been using them all along if you

look on the first line here we are

calling max on the second line we are

calling men and on the third line here

we are calling incur mult to do whatever

it does okay when you start splitting

your functions between the definitions

and the declarations remember the one

definition rule and this says that you

can't have a function defined

multiple times in your entire c-plus

class application if you do that the

lincoln stage is going to find those two

not know which one you really want to

use and you're going to get a linker

error we're going to see that when we

hit visual studio code in a minute

another thing is that you know that your

definition can really leave anywhere in

the linker is smart enough to parse your

the definition for whatever function

it's found in your source code and it's

going to keep looking until it finishes

looking in all translation units and

when it doesn't find the definition it's

going to give you a link error which is

probably going to say undefined

reference to something and we're going

to see an example of this in a minute

okay now that you know about this

updated compilation model and you have

an idea that we can split our functions

across multiple files we're going to

head over to visual studio code and play

okay here we are in our working folder

the current project is multiple files

here we're going to grab our template

and put that in the project of interest

and we're going to open this in visual

studio code let's do that we're going to

open the folder i'm going to choose the

and we are going to open up the main cpp

and clean it up a little bit we are

going to set up a max function and

remember the function has to show up

and uh we are going to split this into a

definition and a declaration i think we

already know how to do that so let's do

put a definition down here and we're

going to change what we have on top here

into a declaration let's say that to be

super clear and what we have down here

is a definition and we can call this

function we're going to set up the

variable which is going to store our max

and we're going to assign whatever we

to max here so we want to find the

maximum between 34 and 56 for example

and we're going to print this out i'm

going to say max is the maximum

and if we boil and run this program

let's use gcc to do that we have a

compiler error here what is that we need

a semicolon not a column here

i think the squiggly line is now going

to go away and our things are named the

same way the compiler is not going to

like it let's bring up a terminal so

that we see our problems tab expression

preceding parentheses or parallel must

ah okay the problem here is that these

two guys max and max are called

the same and this is going to confuse

the compiler a little bit so what we're

going to do is call this maximum

and we're going to do maximum here

and the compiler is going to be happy

now we can compile and i've built this

program world is good and if we run it

we should get our maximum printed out

let's see that the maximum is 56

and if we change 34 here to be 134

and both again we should grab that as

the maximum let's see if that's the case

run the program the maximum is 134.

so this is working exactly as we want

the next thing we want to do is to split

this function across multiple files so

we're going to set up two different

files one is going to be a header file

the other is going to be a cpp file and

you have to follow this structure in c

plus so we're going to go on the left

here and add a new file in visual studio

code you can click on this little icon

that says new file to create a new file

once you do that you're going to be

given this little window in which we can

type the name of the file we're going to

dot h it's going to be our header file

and we're going to add another one which

is going to say compare that cpp okay

our two files are going to be compare

and they are going to contain

our functions to compare stuff so we're

going to have in a function called max

and another function called men for

computing the minimum let's go there and

actually do that we're going to move our

declaration in the header file

so your declarations are going to be

leaving in header files and we're going

to grab our definition and move that

compare.cpp so i'm just going to cut it

out and paste that and compare cpp here

once we do that we're going to go back

and see that we have a problem now

the main function doesn't know what this

max function is because it's not

declared anymore and if we're trying to

compile our program we're basically

going to get the same error we see here

and visual studio code identifier max is

undefined because it doesn't know what

this function is if we ignore this and

try to weld let's do that we are

learning so no big deal here we're going

much weirder error but the message is

going to be the same maths was not

declared in the scope so the compiler

doesn't know what to do with whatever we

typed here but there is a way in c plus

plus we can solve this problem by

including the header that contains our

declaration for the function that we are

using here we can go back in main and do

that and we're going to say include and

that's going to bring in our header and

if you wait a minute you're going to see

that the squiggly line is going to go

away so what happened the preprocessor

is going to come in and copy whatever we

have inside compare.h it's basically

going to go and compare that age copy

everything we have in here and come back

in main and paste all that in the place

where we have the include directive here

this is called an include directive or

an include preprocessor directive this

is what the preprocessor is going to do

here and now if we try to build this

program let's try to do that we should

be fine world finished successfully and

we can run our program to see the

maximum printed out let's run rooster

maximum is 134 now everything is working

let's add another function here because

just having one function is really

boring so we're going to put in a main

function it's going to type into a and

and we're going to go in the cpp file

and put in another definition for the

minimum function here we're going to

let's call this man and we're going to

test for a is less than b this is going

to give us a minimum and now if we go

back in main cpp we will be able to use

our minimum function because it is

protein also by this preprocessor

directive we have here so we can go down

and say end minimum and we're going to

and 23 why not and we're going to print

the minimum here and we're going to

the bullet is going to be good if we run

this we should see both the maximum and

the minimum from these calls we make

okay by now you should have an idea

about how to split your functions across

multiple files you should also know that

you will have to include whatever header

contains the declarations for the

functions that you want to use another

thing i want you to see is that the

definitions for your functions don't

have to live in a file that is named the

same as the header file for example here

our header file is called compare and

the comparison tpp contains our

definitions but the definitions don't

have to live here they can really live

in any translation unit that you have in

and our c plus plus programs the

translation unit is mostly equivalent to

a cpp file so let's set up another file

and show you that we can move this

definition there and the program is

going to keep working we're going to add

another cpp file and call it some

that cpp it has to be a cpp file because

implementations and let's take the

implementations for example let's take

them all put them in another file why

we're going to grab all these guys here

let's catch them out and put them in

and i'm going to build this and see that

because the linker is smart enough to go

and whatever translation units that we

have set up in our project here and you

see the world is good we can upload this

we can run this i should say and we're

going to have our output here we can

even take one of these guys let it leave

compare.cpp file for example let's take

and we're going to bring that

back and we're going to work notice that

our maximum function is living in some

other file and that the minimum function

definition is leaving and compare that

cpp but if we will this is going to work

going to parse all the translation units

definition it needs to find and in this

case it will be looking for the maximum

here and it's going to find that in some

minimum function here it's going to be

looking and compare and it is going to

find it and the world is going to be

good and we can run the program again

one thing i really need to point out is

that if the definition is not available

let's say the minimum function here is

not there we can comment it out to hide

it to the compiler or hide it from the

we will get a linker error let's try to

uh-huh world finished with errol's the

terminal process terminated with execute

code -1 but the main message here is

that we have an undefined reference to

min and and so when we compile the

compiler is going to be happy with the

declarations that it has found in our

compare.h file if we go there we see

that we have a declaration for max and

the declaration for man the compiler is

going to be happy it's going to compile

our code and when the compiler compiles

it's going to generate object files and

it will hand the job over to the linker

to stitch all those little object files

together to have one single binary file

once the linker tries to do that it's

going to look at main because that's

where it's mostly going to start from

and it's going to see uh-huh main is

calling minimum here where is the

definition for the minimum function it's

going to parse every single translation

unit in the project it's going to come

here and compare that cpp it's not going

to find it it's going to look in

main.cpp it's not going to find it it's

going to look in some other file it's

not going to find the definition and the

i didn't find my definition for the

minimum function so i'm going to throw a

linker error and you the developer

you're going to fix this problem and

you're going to see this error here and

again this is a linker error gcc doesn't

more visible stuff to show you that this

is a linker error but what you should

look for is ld returned 1 here because

ld is the linker that gcc uses so this

i think i should show you how a linker

error looks if you are using a microsoft

compiler so we're going to build again

but now we're going to build with msvc

if you don't have visual studio that's

not a problem you can keep using gcc but

i just want you to see how different

compilers handle these arrows i have the

luxury to do that because i am

developing this course on a windows

machine and i have a microsoft compiler

handy that we can use directly from

visual studio code here so i am going to

and you're going to see that it is going

to start welding it is building

and it is going to fail and throw a link

arrow also so you see here some other

this object file was being taken and

stitched together with other object

files to put together a binary it didn't

find the definition for the minimum

function and it is going to throw a

linker error and in visual studio you're

going to have a problem like this l and

and it's going to give whatever version

of the compiler you are using but down

here you see unresolved external symbol

this is how visual studio says it and

an undefined reference to something this

is just visual studio's compiler's way

to say this and again it's going to say

it is basically the same error we saw

when we were using gcc in a minute video

studio the compiler from microsoft is

also going to put a lot of junk in our

folder here so let's remove all these

things i'm going to select them all

and they are going to go to my recycle

bin and we have another one here we

should remove let's remove it

and now we should go back in some other

file.cpp or compare.cpp that's where we

have a minimum function we can activate

it and if we're both now the world

should be good because the linker is

going to find this definition here

okay let's build with gcc because that's

now you see that the world is good we

can clear and run rooster and our

program is going to work as it should

this is really how you can split your

functions across multiple files the

headers are going to contain the

declarations the cpp files are going to

contain the definitions your definitions

can really leave anywhere it's going to

be a matter of what works better for

your project but for organizational

purposes your cpp files are going to be

basically like this you're going to have

some declarations in the header like

and in a corresponding cpp file you're

going to have and the definitions for

whatever declarations you have in the

header but you don't have to do it this

way if it makes sense for your

definition to show up somewhere else

please go ahead and do that c plus plus

is going to accept that this is really

all we set out to do in this lecture but

before we go i'm going to give you a

chance to set up another function

suppose we have a function called

anchor malt and we're going to have the

function set up in here we're going to

we already know how to do these things

we've used this example a couple of

and that's what we're going to return

now your job is to split this function

a declaration and a definition and put

those in two separate files one is going

to be called operations.h and the other

operations.cpp pause the video go ahead

set up your project like that and call

that function in main cpp and see if you

can pull that together okay post the

video do that and once you are done come

back again and see how i do this so

we're going to set up a new file called

it's going to be a header file dot h and

we're going to add another file called

that's going to be our cpp file which is

going to contain our definitions we're

going to go back in main and grab the

entire function here we don't want it in

we should go in the operations header

and we're going to put in our definition

and we're going to put in our

declaration the declaration doesn't have

a body so we're just going to put a

semicolon at the end here you already

know this we're going to go in the cpp

file and put in our definition

this is going to work and to be able to

corresponding header here why is this

it's cpp we're going to rename it

and we're going to change this to cpp

now we should be fine we should have our

properly and uh to use this function we

will need to include the corresponding

header which is operations.h

let's do that we're going to go in main

and notice that the way we include our

own headers is different from the way we

the libraries or headers that come with

the c plus plus standard library this is

a conversion that is used by many

compilers this is how we will have to do

things please remember this if you are

including your own header please put

in the quotes like we do here if you are

including a standard library header

please use angle brackets like this now

included we can go down here and say

we're going to set up two variables x

why not we're going to have a 4 here

and we're going to have a y which is a

five let's do that and we're going to

have an integer to store our results

it's going to say anchor mount and it's

going to do the operations on x

and y let's do that and we're going to

print the results here so we're going to

and it's going to be whatever we have in

okay if we build this program it is

going to work we're going to use gcc to

world the world is good if we run it we

see our output here going to run rooster

and the result is 24 because

okay if we increment x we're going to

and if we increment a 5 we're going to

if we multiply these guys we should get

a 30 and that's not what we have here so

what is happening let's look at our

because we want to increment immediately

and we are going to clear and run

rooster now we have the result that we

expect let's go back in main and look at

our program this is what we are using

here and this is the output we expect

this is really all we set out to do in

this lecture showing you how you can

functions across multiple files this is

really good if you want to organize your

project for example somebody who comes

to the header here is not going to be

bothered by looking at all the

definitions and the details of how we

compute this maximum and minimum and we

have the flexibility now to move our

headers in some other file because we

really want to keep the main function or

the main file here really clean we don't

want all those definitions to show up

here because it is possible for your

project to contain hundreds or even

thousands of definitions if you make all

those declarations show up in the main

cpp file here that's going to be really

hard to follow and work with now we have

the flexibility to split those guys

across multiple files and we can even

use lots of headers if that is what is

going to work for our project this is

really all we set out to do in this

lecture i hope you found it interesting

we are going to stop here in this one in

the next one we're going to see how we

can pass parameters to functions by

value go ahead and finish up here and

in this lecture we're going to see what

is meant by passing parameters to a

function by value and we're going to

look at an example of that here we have

a simple function called say age it's

going to take one parameter which is an

integer called age and in the body of

the function we are printing out the age

after incrementing it suppose this is

for your program the function is split

into declaration and definition we have

a declaration on top here and we have

our definition below the main function

in the main function we will attempt to

use this function we're going to call it

down here and we're going to pass a

local variable which is called age as

our age when we do that we expect this

to print you are 24 years old because

we're going to increment the age and

we're going to say hello you are 24

years old this is what this program is

going to do but we want to keep track

of how the outside variable here is

going to change and the age we have

passed as a parameter here because this

edge we pass as a parameter is not going

to be the same as the age we have on top

here what we pass here as a parameter is

going to be a copy of the actual

variable that we passed here and this

mechanism is called passing a parameter

by value and what you really pass is

going to be copy and what you work on

inside the body of the function is not

going to be the original stuff you

passed as an argument to the function so

we're going to try and prove that here

we're going to print the age before we

call the function we're going to print

the age after we call the function and

what we print here is going to be the

outside variable because here we are in

inside the say edge function what we're

going to be modifying is a locker copy

so we expect the edge here to stay the

same before and after the function call

so the way this is going to work when

control has this function here it's like

we're going to have a situation like we

have here on the left we're going to set

up local copies in the function that are

going to contain whatever was passed as

an argument to this function and this

edge here was passed as an argument to a

function so we're going to have a local

copy of this h and we're going to store

it and it is what we're going to be

manipulating in our program when the

function goes out of scope the local

copy is going to die and the outside

variable we have here is basically going

to be unaffected let's head over to

visual studio code and show you this in

okay here we are in our working folder

the current project is passed by value

we're going to grab our template files

and we're going to put them in place in

the correct project and we're going to

open this up in visual studio code let's

do that we're going to open the folder

that contains the project pass by value

let's do that we are going to open it up

and i'm going to go in the file and

clean it up a little bit and we are

going to set up a function it's going to

and it's going to take an integer which

and inside we're going to increment our

h i think this is what we saw in the

slides and we're going to say however

many years you are old we're going to

age old and we can set up a variable and

the main function we're going to call it

and it is going to contain 23 as our age

we're going to say age and we're going

to pass in our age here we can do that

if we're trying to run this program

let's try to do that we're going to

build with gcc and we are going to bring

in a terminal we can use to run this

visual studio code here let's run

booster we're going to say hello you are

24 years old and this is what we expect

because when this function is called

we're going to increment the age then

we're going to say the age but we want

what happens to the outside edge ear

if we modify the inside edge that we

have on this function here that was

passed as an argument and again what you

pass when you are declaring your

function is the parameter and what you

pass when you are calling the function

is called an argument in c plus plus

please remember this okay what we pass

as an argument is our anti-age variable

which is local to the main function

and we're going to see what happens to

i think this is descriptive enough and

we're going to print that and we're

going to go after the function is called

we're going to say the same thing but

we're going to say after call

by after we mean after we call the

function say h here i think this is

descriptive enough and we're going to

see that if incrementing the local

variable to the function here affects

the variable that we have and the scope

of the main function okay so let's see

that we're going to build with gcc as

and the wealth is good so let's clear

and run rooster you're going to see that

before the call we have 23 and after the

call we have 23 we didn't change the

this is a classical copy paste error

for our program to really be descriptive

okay the world is good we can clear and

run rooster and now we have before call

23 after call age is 23 it wasn't

changed by what we have inside here and

we can even go further and look at the

memory addresses of these guys

here we can try and print the address of

the age variable let's let's do that

and put that out here we're going to say

no big deal here we can close the pane

on the left here because it is taking up

valuable space and we're going to go to

the second statement and put in the

and we're going to print that out we can

and when we hit the body of our function

here we can also print the address of

address of age let's do that here and

we're going to print the address of the

local edge variable here which was

passed as a parameter here okay now we

can build our program and watch those

addresses we're going to build with gcc

the world is good we can clear

now you see that the outside variable is

going to leave at an address that ends

and the local variable is going to leave

at an address that ends in dc0 so this

is a completely new memory location that

we are using and it is just going to

contain a copy of what we passed as a

parameter here and the compiler is going

to take care of setting up this copy

variable and have it available for use

in the local function here we don't have

to worry about that but we have to be

aware that what we are working on and

the same age function here is a copy

it's not the original value this is

really all we set out to do in this

lecture making you aware of the call by

value mechanism and the main message is

that what you are working on in the body

of your function when it is called is

going to be a copy of what you have

passed as an argument when your function

in this lecture we're going to see how

we can pass parameters to functions by

pointer this is going to allow us to

avoid the copies that we were

experiencing when we were passing

parameters by value like we have seen in

the last few lectures here is a simple

example showing the syntax we can use to

on top here we have our function

declaration and down here we have our

function definition and you see that the

syntax is the same we are passing by

pointer and by pointer and the

definition here and another thing you

should be careful about is that when you

call a function that passes by pointer

you have to give it an address and

that's what we are doing here so we are

passing the address of our age variable

which is going to be passed by pointer

when we pass by pointer we want to be

modifying a copy inside the body of our

function if you look here we are

incrementing the edge variable but we

are doing this through the referencing

so when we pass a pointer here the

pointer is going to contain the address

and in the body of the function the

pointer we will have this edge pointer

is going to be pointing to the original

variable here okay so this edge pointer

is going to be pointing to the original

when we dereference it and modify the

variable we're going to be affecting the

original variable i really hope this

makes sense and this is really what

passing by pointer is all about you

declare your functions by passing in

pointers like this and in the definition

you do the same and when you call the

function you need to pass in an address

of the variable because that's what we

store in a pointer here and this is

going to work if we try to run this

example here we're going to print 23

because that's the original value we are

going to call the say age we are going

to increment and this is going to change

the original value if we print here

we're going to get 24 and when this

function terminates we're going to hit

this statement here and we're going to

print 24 this is what we're going to see

when we get to run this program here and

this is really all there is about

passing by pointer we are going to head

over to visual studio code and play with

us a little more okay here we are in our

working folder the current project is

passed by pointer we are going to grab

and we're going to put them in the

current project which is pass by pointer

we are going to open this in visual

studio code pretty quick we're going to

choose that pass by pointer we open this

and our main cpp file should show up

we're going to clean it up a little bit

we are actually going to grab the code

from the last lecture and put that in

here and that's going to be our starting

point let's close the left pane here so

that we have some breathing space the

function here say h is going to pass by

pointer so we should take out this cost

and uh have a pointer here like we had

in the slides we're going to do the same

definition here if we go down we're

going to do that we're going to pass by

pointer and we are going to uncomment

the line that increments our age here

okay after we do that you see that we

have a squiggly line at this line that

calls the say age function what we need

to do is to pass it the address of the

edge variable here like we saw in the

slide so this is the syntax we have to

once we do this this program is going to

be valid and if we run it here we're

going to print 23 because that's the

value we have in here we're going to

call the say age function we are going

to increment age and here we forgot to

do our dereferencing so what we need to

do here is to dereference the age and

increment it this is going to increment

the original variable here and we're

going to be accessing this through the

the referencing operator of our pointer

here if we hit this line and the

function here we're going to print 24

incremented through this statement here

and after the function call we're going

to hit this statement here on line 10

and it is going to print 24. this is

take a moment to make sure you really

understand this the things you need to

be careful about is the syntax we use to

declare the function here we say that we

are passing by pointer because of this

little star here and we have the same

thing when we hit the definition of the

function we have this little star so we

are passing by pointer another thing you

should remember is to pass the address

of a variable when you call the function

like we do here and please remember to

use the the reference operator whenever

you want to modify whatever variable is

leaving at the address that you passed

in here so that's why we are the

reference in here through the star

operator like we are doing here this is

really all you need to be careful about

so we are going to try and run this

program let's do that we're going to

the boiler is going to go through we

so that we can run this program and

again we expect to see a 23 24 and 24

okay here is our output before we call

the say age function the age is 23 the

address is dec when we hit the function

uh years old so here we should have the

reference to access something inside the

variable here so we should say you are

age old we need to dereference this guy

because now it is a pointer i forgot

that i really am sorry but we are

this is a good learning chance for you

not to make the same mistake as i am

making here so let's try and build again

we should see the correct output we are

and run rooster now we see that before

ages 23 when we call the function h

becomes 24 because we just incremented

through our reference operator and after

the function call the edge is going to

because we have modified the original

variable here through our the

referencing of the pointer here this is

really all there is about passing by

pointer this is the syntax you have to

pass a pointer in the declaration you

have to pass a pointer in the function

definition and when you call the

function you have to use the address of

the variable and pass that as an

argument to the function and whenever

you need to use the past parameter

you're going to go through the the

reference operator like we did here

and here in the body of our function

in this lecture we're going to see how

we can pass parameters to a function by

and this is another technique we can use

to avoid passing by value which is going

to create a copy and the syntax is

really simple if you look at the

declaration here you're going to see

that we say and reference and again if

we hit the definition we're going to say

into reference as you see here

when we call the function we don't have

to pass the address of operator we just

passed the variable because this is

going to be treated as a reference by

the compiler and in the body of the

function we don't have to go through

ugly the referencing like we did with

pointers and hopefully you can see that

if you want to avoid copies passing by

references is much cleaner you don't

have to use the address of operator when

you call the function like we do here

and you don't have to go through the

reference and to access and modify your

variables and the modification we do

here by incrementing age is going to be

seen on the outside because we are going

through a reference and the reference is

a true alliance to the variable that the

reference is referencing so by

incrementing the edge here and the body

of the function the change is going to

be seen after the function call before

the function here we're going to get 23

in the body of the function we're going

to get 24 because we just incremented

the function and after the function call

we're going to get a 24 because the

change was propagated to the original

variable and the reason is because we

are going through a reference here

let's head to visual studio code and

actually play with us a little more okay

here we are in visual studio code the

current project is passed by reference

1710 here so we're going to grab our

template files and put them in place

let's do that and we are going to open

this in visual studio code pretty quick

let's do that the main cpp file is going

to show up here again we are going to

grab the code from the last lecture and

use that as a starting point and we're

going to be modifying the signature of

our function here so what we want to do

is to pass by reference we're going to

say enter reference here you already

know references from a previous chapter

and we are going to hit the definition

here and do the same thing so let's say

and when we call the function we don't

need to pass the address of operator

because this is a reference we can use

it right away the compiler is going to

know that this is going to be a

reference to the original variable that

and in the body of the function let's

take out this last line here we don't

need it and in the body when we want to

the reference we can do that right away

without the referencing so we can just

say plus plus h here and the changes are

going to be propagated to the original

variable here because we are going

through a reference let's go down and

modify this because this is a reference

and we can close this left pane here so

that we have some more breathing space

and you see that visual studio code is

no longer giving us any squiggly lines

so this must be valid c plus plus code

again notice the syntaxes we are using

here we are passing a reference in our

declaration we are passing a reference

in our function definition here when we

call the function we don't need to do

any address of operator we pass the

and in the body of the function we don't

have to do any dereferencing we can

or modify the variable however we want

the changes are going to be propagated

to the original variable because we are

incrementation here is also going to

affect the original variable that was

declared in the main function here let's

take this out and down here if we need

to use our variable we're going to just

use it right away we don't need any

referencing and if we print the address

of age here we're going to see the same

address we see on the outside because

this is a true alias it's going to be

referencing the same variable that we

have in main here okay now that you have

a better idea about this we are going to

try and build this we're going to use

gcc as always you can see that the build

if we bring up a terminal to try and run

we can clear and run rooster

we're going to see that before we call

the function the h is 23 but the address

when we hit the function the edge is 24

because we just incremented that here

but notice that the address of the

variable is the same as on the outside

so we are modifying the same variable

and when the function is done the edge

is still going to be 24 because we just

modified the original variable through a

reference here okay this is the effect

of passing by reference you can use a

claim syntax to modify the original

variable in your functions and this is

going to avoid copies like we have seen

when we were passing parameters by value

a few lectures back i would like to

welcome you in this new chapter where we

will be focusing on how to get data out

of functions again the model of the

function is really what you see here it

is like a machine and you can give input

to that machine and you expect to get

something out of that machine this

chapter is going to focus on this part

and we're going to see the different

facilities offered by the c plus plus

programming language to get output from

functions and we are going to start in

the next lecture and see how we can use

input and output parameters go ahead and

finish up here and meet me there in this

lecture we're going to see how we can

use function parameters to get data out

here is a simple example and we have

three functions here we have max str

max and and max double and you notice

that we have three parameters for each

of these functions the first two

parameters are going to be input they

are going to get data and the function

and the third one is going to be the

output parameter and it is going to get

let's focus on max hdr here and really

drive the point home the key idea here

is that for the third parameter

we are using a modifiable reference and

if we use a reference the changes we do

inside the function are also going to be

visible on the outside and we explicitly

left out the const that we have on the

other parameters because we want to be

the output variable here inside the

function if we marked the third

parameter as const we would get a

compiler error if we're trying to do

something like this and assign something

to the output parameter here so the main

purpose of this function is to compute

the maximum between these two strings we

are going to say if input 1 is greater

then input 1 is going to be our maximum

and we are going to store that in our

output parameter here if input 1 is not

greater than input 2 then input 2 is our

maximum we're going to store that in our

output and whoever has access to input 2

outside the function is going to see the

changes that we are making in the body

of the function this is really the

send output from the function and make

when the function has returned and again

the key idea is that we set up the

function in a way that the changes we do

inside the function are going to be

visible on the outside and we are able

to do that because output here is a

reference this is really key we have

used references here but we can set up

the same thing using pointers because we

have seen that with pointers we can also

make our changes inside the function

visible to the outside the two other

examples here are really extensions of

the same thing we have two input

variables input 1 and input 2

output is going to store the output from

the function you notice that output is a

reference and because of this the

changes we do in here are going to be

visible when this function has returned

and we do exactly the same thing on max

but you see that it is using a pointer

okay i really wanted you to see this so

inside we're going to try and figure out

who is the maximum and if input 1 is the

maximum we're going to write that in our

output variable here and you notice that

we are the referencing here because this

guy is a pointer and if input 2 is our

maximum we're going to write that in our

output variable here one thing i don't

think i explained here is that we have a

cost std string reference here for maxed

hdr and the reason is that the input

variables aren't really meant to be

changed that's why we market them as

cost and if you want to modify them in

some way you can take the const away and

it is going to work okay this is really

the big idea we are playing with in this

lecture using function parameters as a

way to output data from the function and

here are a few ideas you should keep in

mind output parameters should be passed

in such a way that you can modify the

arguments from the inside the functions

and we have seen that we have two ways

to do that we could either use

references or even use pointers but

references are what you should prefer in

modern c plus plus input parameters

shouldn't be modified they are meant to

just get data in the function and that's

why in most cases you're going to see

that they are marked const okay now that

we have seen all these ideas i think it

is time we headed over to visual studio

code and actually played with them okay

here we are in our working folder the

current project is input and output

parameters we are going to grab our

template files like we always do we're

going to put them in place and we are

going to open this guy in visual studio

code we're going to just drag it and

drop on top of visual studio code here

and it is going to open up we have our

main function here we can close the pane

here and clean the file up a little bit

we're going to remove what we don't need

here and we're going to have a bare main

function we can play with here the first

thing we're going to do is to put in our

max str function it is nothing special

we just have two input parameters and

one output parameter the output

parameter is going to be what we use to

get output outside the function and

inside we're just going to compute the

maximum if input 1 is the maximum we're

going to write that in our output

parameter if input 2 happens to be our

maximum we're going to write that in our

output parameter because our output

parameter is a reference the changes we

make inside the function are going to be

visible on the outside because we will

be working on the original variable

through the reference which is really a

true alias here okay now that we have

the function set up like this we can

head in the main function and try it out

we're going to set up three variables of

type std strand i think we should

include the string library here let's do

that and we're going to have an out

string which is going to be our output

variable and we have two input strings

one is initialized with alabama the

other is initialized with bell view and

we're going to call our max sdr function

here you notice that it's not going to

be using the return mechanism we're

going to be grabbing the output from

this function using an output parameter

which is going to be our out hdr

variable here okay once the function is

done we're going to have the maximum

stored in our out sdr variable here and

we can print it out now that we have

this setup we can actually try and build

this we're going to use gcc let's do

that the build is good we can bring up a

terminal and clear and run rooster now

you see that the maximum is going to be

bell view let's try and change this to

casablanca why not and we're going to

see that the maximum now is going to be

casablanca and our function is going to

be smart enough to store the maximum in

this output variable here let's build

again the world is going to be good

going to clear and run rooster now the

maximum is casablanca hopefully you

understand that we are able to make the

changes in the function processed

because our output parameter here is

passed by reference this is a true

reference and any change we do to the

output parameter here is going to be

visible in whatever variable you passed

as an argument for this third argument

here this is what is making this work

now that this is working we're going to

put in another example for you to play

with the next function we're going to

play with is going to be max and as you

see here and it is very similar to our

max hdr but you notice that our inputs

are no longer references because we

don't really mind copying fundamental

types in c plus plus they are small in

memory so copying them is really cheap

we can pass them by value and this is

not going to be so wasteful in our

program but the first parameter must be

passed by reference because we want to

use it as an output parameter and we're

going to use it to get output from the

function and the way we're going to do

that we're going to write whatever

variable is the maximum in our output

parameter and the changes are going to

be visible on the outside now we are

going to head over in our main function

set up a few variables and play with us

so we're going to say and out and this

is going to be our output variable and

we're going to say input one let's say

in one and we're going to initialize

this with a 45 why not and we're going

to say ent in two and we're going to

initialize this with 23 why not now that

we have this we're going to say max and

and we're going to put in our input

we're going to say n1 and n2 then we're

going to say out and as our output

variable now that we have this we can

actually print out whatever number is

the maximum through an output statement

like this really simple we're going to

say max and and we're going to say out

to end that's where it is going to be

stored and we are able to do this

because again the third parameter here

is passed by reference and any change we

do and the function here is going to

stack even when the function here has

returned and we're going to have that

stored in our third parameter here and

this is a really common technique

especially in code that has to interface

with c code out there from c plus plus

and you really need to be aware of this

now if we run this program we're going

to see our maximum printed out and it is

going to be stored in our out variable

here let's do that we're going to use

gcc to world the world is good you can

clear and run rooster and you're going

to see that the maximum is 45 if we

change and store our maximum in into

here and for example let's make this a

let's build it in to take the changes

rooster.xe binary we're going to clear

and run rooster and you're going to see

that that's the maximum here we are able

to grab whatever is the maximum from

these two input parameters and store

that in our output parameter here

because we are passing that third guy as

a reference this is really important we

have seen that we can use references to

make changes we do in the function stick

and be visible in outside variables but

we can also use pointers and i am going

to show you an example of how we can do

that first we're going to comment this

out because we don't want noise output

in our program and we are going to go on

top and set up a max double function

which is going to grab our output using

pointers the name of the function is max

double it's not going to return anything

and it is going to take two input

parameters input 1 and input 2 and it is

going to tell us whichever of these 2 is

the maximum the maximum is going to be

stored in our output parameter but we

are using pointers to make these changes

inside the body of the function stick

and be visible on the outside of the

function so we are going to the

reference here because the third guy

here is a pointer and we're going to

store in whichever is the maximum and

when the function returns the maximum is

going to be visible on the outside so

let's go down and try this out we're

going to say double out double and we're

set up our input here we're going to say

in double one and we're going to make

45.8 why not and we're going to do a

second input parameter and int we should

say n not end sorry for this in double

for input double so we're going to say

double 2 and we're going to initialize

for example we can really put in

anything now that we have this we can

call our max double function let's do

that going to say max double we're going

to say in double one and in double two

let's do that and we're going to have

out double as our output parameter and

uh because it's a pointer we need to

pass this guy as an address so we're

going to say address of how to double

here that's how we're going to be able

to manipulate that inside the function

here once we do this we are going to

have our maximum stored and out double

and we can print that out so we're going

to say stdcl max double and we're going

to say mac and we're going to say out to

double std e and el and if we weld why

do we have a squiggly line here we don't

have a semicolon at the end of our

function called here so we're going to

build with gcc as always you're going to

see that the world is good we can clear

if we change and store our maximum and

in double to here we can change this guy

we're going to build and see that we are

actually grabbing the maximum regardless

of the variable in which it is stored if

we run rooster we're going to have our

maximum and this is working exactly as

we want this is really all we set out to

do in this lecture showing you how you

can use references to use parameters as

output channels for data to get outside

of the function and be used in variables

that are outside the function here i

really hope this makes sense and this is

a technique you need to be aware of

we're going to see other techniques to

do the same thing and uh starting in the

next lecture we're going to see how we

can return from functions for now i hope

you found this lecture interesting we

are going to stop here in this one in

the next one we're going to see how we

can use the return mechanism to get data

outside our function go ahead and finish

in this lecture we're going to see how

we can get data outside of a function

through the return mechanism and this is

going to be an alternative to the way we

have been doing things in the last

lecture where we used function

parameters as channels to get data

let's look at the simple example of how

this is done here we have a simple

function called sum the function is

and it is going to sum up two parameters

that we pass to at nta and end b

if we get inside the function we're

going to do something really simple

we're going to set up a new variable

which is local to the function we're

going to call that reserved it's going

to be the same type as our input

parameters and we're going to add up a

and b and store the results back in our

once we have this we're going to return

this for this variable to be visible by

whoever called this function here one

thing you should know is that this

variable is local to this function here

and it will be destroyed the moment we

hit the end of the function here and the

so if we go in main here we're going to

try and see an example of how we can

call this function we have two variables

a and b and we have a new result

variable set up in the main function

please note that this variable is very

different from the variable we have and

sum function here because they live in

different scopes okay we are calling our

sum function here and we are passing it

two arguments in the form of a and b

here the function is going to compute

our sum and it's going to return it and

we're going to store that back in our

local variable to the main function here

the result variable here again is local

to this main function okay once we call

this function we're going to have our

results stored in here and if we print

like we do here we're going to see it

printed out on the console in this case

it's going to print 50 because 34 adding

16 that's going to be 50. but one thing

i want you to know is that this is going

to return by value and what we mean by

this is that we're going to copy

whatever we return here and store a copy

of that in this result variable that we

have in the main function and we're

notice the stdc out statement we have

here this is going to print the address

of this local variable and once the

function terminates we're going to try

and print the address of this resort

variable in the local scope of the main

function and we're going to see two

different addresses and hopefully this

is going to prove that we are returning

a copy it's not the original variable

that we have in the sum function here

that we are returning okay hopefully

this drives the point home that we can

use the return mechanism to get data

outside the function and we're going to

grab the result in our result variable

here and we're going to use it however

but things don't always work like this

sometimes the compiler is going to

and not really returned by value but

returning by value is the default but if

the compiler notices that it can do

things better it is going to optimize

your returns by value to return by

reference and you're not going to make a

copy but you're going to somehow reuse

the local variable in the main function

let's look at a simple example to really

drive this home we have a function here

which is going to add strength it is

going to basically concatenate them

using the plus operator here and you

notice that inside the function here

we're going to set up a local variable

which is going to store our concatenated

and we're going to print the address of

the local string after that we're going

to return the strength so that it is

usable by whoever calls this function

let's go in main and see how we can use

this function here we are setting up a

variable called sdr result which is

going to store our result strength we

are saying add strings here we are

calling our function and we are passing

in two strings hello and world and we

want to concatenate these guys this is

going to give us our result and if we

print it out we're going to get hello

world printed out but the main message

here is that the address of the outside

string here is going to be the same as

the address we have on the inside here

and this is going to mean that the

to return the local variable because it

has seen that we could really be wasting

this guy here inside the function when

the function returns this string result

here is going to die off but the

compiler knows that we can reuse that

and avoid the work of copying this

string which might be really large

suppose this string has a thousand

characters inside and copying it would

be a waste so the compiler is not going

to return by value which is the default

it is going to do some kind of return by

reference but it's really not a return

by reference because this is a local

variable we can't really have a

reference to a local variable to a

function that would be really bad

because we might be able to modify it

when the variable is actually dead after

the function has returned so it is a

magic that the compiler is doing to save

you from unnecessary copies but you

should be aware of this and not make

your code rely on returning by value

okay now that we know this we're going

to head over to visual studio code and

actually play with us here we are in our

working folder the current project is

returning from functions by value we're

going to grab our template files pretty

quick we're going to copy them let's do

that and we're going to put them in the

and we're going to open this guy up in

visual studio code pretty quick let's do

now we have our main cpp file here we

can clean it up a little bit

and close the left pane here because we

don't need it the first thing we're

going to do is to put in our function

which is going to compute the sum of two

integers and return as the sum of these

two guys inside the function we're going

to set up a result variable which is

going to store the sum and we're going

to return it and it is going to be

visible to whoever has called this

function here again i am going to

emphasize that this is going to return

by value so what we return is really

going to be a copy of this variable here

and we're going to prove that by

printing the address of this variable

inside and outside the function here so

we're going to set up two variables in

main we're going to say and x let's call

our input parameters x and y we're going

to put in a five and the second guy is

going to be a y and it's going to store

an n9 why not after that we're going to

set up a variable which is going to

store the results let's call this result

why not and we're going to say some x

and y okay we are passing these guys by

value because we don't really care about

copying and and it is a fundamental type

it is really small in memory so it's

going to be very cheap to copy it's not

going to hurt the performance of our

application but what we want to do now

the address of the reserved variable in

the main function here and see that it

address of the variable we have inside

here another thing you should watch out

for is that we are able to get data

outside the function here the sum was a

local variable but we are able to get it

out of the function through the return

mechanism here okay before we go ahead

and run this program we're going to fix

the statement here we forgot to change

this to say out to mean that it is

outside the function here that's the

meaning we're going to build with gcc

the world is good we can clear and run

rooster now we're going to see that

inside the function the address of the

and outside the function when we hit

the end of the function here we're going

to see that the address ends in de4 so

this proves that the local variable

inside the function and the outside

variable here in the main function

leaving two different memory addresses

there are two different variables and

the return mechanism here is just going

to copy whatever we have in the local

variable and make it available on the

outside here so that we can assign it to

the reserved variable in our main

function here this is how the return

mechanism is working and it is going to

be returning by value by default it is

going to be making copies this is the

message here now that we know this i

want to show you that there are

if you return by value like this you

won't be really always using separate

memory addresses for the inside and the

outside here and we're going to prove

that with a function that is going to

let's comment what we have out because

we don't want this to confuse us so

we're going to bring this inside our

block comment here and we are going to

go below our sum function here and set

up a new function which is going to be

called add strands it is going to return

a string by value okay it is by value

because this return type here is not

qualified with anything like a pointer

or a reference so by default it is going

to be by value and inside you see we are

doing the exact same thing we did in the

sum function here we are adding up two

strands we are storing the results in a

local variable and we are returning that

but if we run this program you're going

to see that the address on the inside is

going to be the same as the address on

the outside so let's set up something

that we can play with here we're going

to go down in the main function and set

up a few variables we're going to say

hdd strand we're going to say

nstr1 and we're going to store in hello

let's do that and we're going to say std

and we're going to store and world by

now you know what i am trying to do here

i am trying to say hello world okay once

we have this we're going to set up a

resort strike so we're going to say std

strength and i say result str and we're

going to say add sdr and we're going to

nstr1 and in str2 this is how we do this

and after we do this we're going to

print out the address of the variable

here so let's do that and it is going to

be the address of result hdr let's say

that here and we also need to print the

actual result of this operation here so

let's do that we're going to say sddc

out result sdr we're going to print the

strength i don't think we did that on

sum function here but we can quickly go

there and prove that to you so let's

comment this out sorry for this this is

going to be confusing but i don't want

so we're going to see that if we print

this out we're going to get the sum

which is 14 printed out let's do that

pretty quick we're going to go down and

say sddcl and say result and we're going

to say result and we're going to build

it pretty quick with the gcc and if we

clear and run the rooster we're going to

see the result which is 14 here and you

can change these guys up to really play

with us for example if we make this 15

and put in a 9 we're going to get a 24

printed out let's build again

just to have fun with this and we're

going to clear and run rooster we're

going to get a 24 here now we can

comment this back i am happy i have

showed you this and we can uncomment our

string code here and uh build and run it

so we're going to build with gcc the

build is good we can clear and run

rooster and again what we want to see

is that the compiler is going to

optimize this out it is not going to

return by value like we had was the sum

function where we had the address on the

inside different from the address on the

outside you see here that inside ah we

forgot again to change this guy to out

uh sorry for this so we're going to make

this guy out and we're going to build

again and we're going to clear

clear and run rooster now we're going to

see that inside the address ends in d30

and outside the address ends in d30 this

can be really confusing because we said

we want to return by value by not

decorating our return type with a

pointer or a reference or something like

that it is going to be returning by

value and if you return by value you're

going to make copies and if we made the

copies the address on the inside and the

address on the outside should be

different but they are the same the

reason is the compiler is going to

notice that you are trying to copy

and it is going to see that the variable

here which is inside the function is

going to be wasted when the function

by default this should be really

destroyed and you should copy

because you are returning by value but

the compiler is going to insert an

optimization to do some magic and make

it look like you are returning by

reference and it is really not going to

make a copy so it is going to reuse the

address on the inside and hopefully this

is going to prove this to you the

message here is that you shouldn't rely

returning by value because if the

compiler sees that it can do a better

job than you it is going to optimize

your return by value to return by

reference and you're going to not be

making copies so don't make your code

rely on returning by value and making

copies and you should be aware of these

optimizations that the compiler can do

behind your back i would like to welcome

you in this new chapter where we will be

learning about function overloading

function overloading is a mechanism we

to have multiple copies of the same

function but taking different parameters

for example here you see that we have

different functions but all these

functions have the same function name

and these are said to be different

overloads of the same function there are

a couple of rules you need to be aware

of to be able to set up your overalls

correctly and get them to work and

that's what we're going to be learning

about in detail in this chapter but now

i just want you to see the flexibility

you can get with function overloading

for example here if we have a few

variables in our program we can call the

max function and the compiler is going

to select the most fitting overloading

here so for example if we call our

function with integer arguments the

compiler is going to choose this

overload here if we call a function with

std string arguments the compiler is

going to choose this overload here and

we don't really need to concern

with making sure we have the correct

arguments the compiler is going to

choose the correct function overload for

us and it is going to call it and it's

going to be very flexible to call these

functions from our c plus plus code this

is how function overload can be really

useful we are going to stop here in this

lecture in the next one we're going to

learn about how you can set up function

overloads based on different function

go ahead and finish up here and meet me

there in this lecture we're going to see

how we can overload functions based on

the parameters that we pass to the

function when we are declaring it or

defining it and here is a simple example

to drive the point home here we have a

it is taking two parameters which are of

and by overloading this function we will

have to use the same name as this

function here so the differences really

will be in the parameters that we pass

to the function because the return type

involved in defining the signature of

the function so if we try to set up

another function called max here which

same parameters as our max on top here

the difference is only going to be in

the return type the compiler is not

going to allow us to do this because the

return type isn't really significant

in making two functions different okay

the only way we have to set up a

function which is legal in c plus plus

is to change something about the

parameters that we have here we can

change the types like you see here for

example we change the types to b double

if the types are different we might even

change the order of the parameters you

just have to make sure the parameter

list is different in one way or another

that's how you're going to get this

function to run with the same names here

and if we manage to set up multiple

functions with the same name in c plus

plus these functions are going to be

called overloads of each other okay if

we go down here we have another overload

for the max function this overload is

going to take two parameters and the

parameters are going to be of type

string view they are different from what

we have on top here which is ant so this

is a legal overload for this max

function here and we can use it okay we

really have a few ways we can make our

function overloads by now we can change

the order of the parameter we can change

the number of the parameters or even we

can change the types of the parameters

again function overloads are a mechanism

we have in c plus plus to set up

multiple functions with the same name to

make our code easier to work with okay

now that you know that let's look at a

simple example of how we can call our

overloads we have a few variables

declared here we have ant variables we

have double variables and we have std

and if you go down here we are calling

our max function passing in integers so

the overload that takes integers for

this max function is going to be called

here down here we are passing in integer

literals so this is going to call the

int overload down here we are calling

the function with double parameters or

arguments so this is going to call our

double overload for the match function

here and down here we are passing in our

string view parameters and this is going

to call the overload that takes string

view parameters and the last guy here is

two string literals string literals can

implicitly convert to std string view so

our std string view overload for the max

function here is going to be called

now that we know this we're going to

head over to visual studio code and play

with this a little more okay here we are

in our working folder the current

project is overloading with different

parameters here we're going to grab our

template files like we always do we're

and we are going to open this guy in

visual studio code by dragging and

dropping on top of visual studio code

here this is going to open our project

here we're going to click on our main

cpp file and open it we're going to

clean it up a little bit and close the

left pane here we are going to go on top

here and put in our first max function

here the return type is and in this case

it is going to take two parameters and

it is going to return whichever number

is the maximum and we are taking

parameters in by value and returning by

value here nothing special we can go in

main and call this function and you

already know how to do that i don't

think i really need to do that

but now what we really are interested in

is being able to set up different

functions with the same function name

like we have here because if for example

you take this function and put that down

below we're going to make a copy of it

and only change the return type if we

try to compile this program you see that

even visual studio code is unhappy now

if we bring up a terminal it is going to

tell us cannot overload function

distinguished by the return type alone

so again the message is super clear here

the return type is not enough to make

two functions different because the

return type isn't involved in making the

signature unique what makes the

signature unique is either the function

name or the parameters that you pass to

the function here so we're going to make

this return type back a double and we're

going to figure out a way to make these

two functions different but have the

same name here because sometimes you

one way we have to do this is to change

the types of the parameters that we pass

in here so we're going to make them

double and we're going to make them

double here and this is going to be

valid c plus plus could these two

functions are different even if they

have the same name here they are two

different functions because they take

different parameters so if you try to

integers this one is going to be called

which takes integers n if you call it

with double arguments this guy here is

going to be called let's try and prove

this so we're going to go inside and say

stdc out and overload called i think

this is enough and we're going to go in

the double function here and say sddc

okay once we have this we also have to

change the return type here to double

because it's going to make things a

little bit consistent here but now we

want to go in our main function here

and set up a few variables we're going

to say and x and we're going to make

this a four and we're going to say into

y and we're going to make this a nine

we're going to set up also double

point four to make it a double variable

and we're going to say double

now we are going to call max we're going

to say auto result and say max and

what do you think we're going to return

here so what we really are interested in

is the return type of the result

variable here and the compiler is going

to deduce whatever is returned by this

function if we call the function with x

and y x and y are integers so the

compiler is going to search for a

function that takes integers and it's

going to find this guy here and that's

let's weld and run this program we are

not interested in looking at the output

here we're just going to see this std

out statement here print whatever

function was called okay we expect the

end one to be called so we're going to

see ant overload called on the terminal

here when we run this program so let's

do that we're going to build with gcc

like we always do the world is good so

we can clear and run rooster

we're going to see int overload called

we can set up two functions with the

same name and make them different only

in the parameters that they take and the

differences may be either in the types

of the parameter like we are doing here

they may also be in the order of the

parameters and we're going to see an

example of that in a minute but before

we do that we also need to try this with

a and b and show you that the double one

is going to be called because we are

passing in double arguments here so

let's build again the bullet is good we

can clear and run rooster this is going

to call our double overload hopefully

this really drives the point home

that we can set up multiple overloads

for the same function name and again the

differences are going to be in the

parameters that we pass here we have

been able to pass different types for

the parameters and this was a vehicle c

plus plus code but we can also set up

another overload just by changing the

types and the order of the parameters

let's do that we're going to make the

first parameter here and and once we do

that this is different from any of the

overloads we've had so this is a valid

overload for this max function here this

is going to work we can even change the

order of these two guys and it is also

a valid overload let's put in another

and we're going to change the first

parameter to double and the second one

to end and now we have four overloads

for the max function and again the

message here is that you just have to

make sure the parameters are different

in some way and your overload is going

to be valid and again i'm not telling

you to set up functions like this

because in this case this is really

useless but i am trying to expose this

facility to you so that you can use it

to your advantage if it makes sense for

whatever application you are designing

here so let's go down and put in

meaningful output i think we can come in

here and say the parameters that we are

passing in here so we can say and double

overload called and if we go down here

you can take this out and say double and

overload called and to get any of these

guys to be called we have to pass the

parameters or of the arguments in this

so if we pass in an end which is x x is

in it and we pass in a double which is a

b here this is going to call our

overload which takes the first argument

to be an integer and the second argument

let's prove that we're going to

build with the gcc the bolt is good so

we can clear and we can run rooster and

we see ant double called because x is an

and b is a double if we flip these guys

let's say b and x then we're going to

have the overload that takes the first

argument of double type and the second

argument of into type to be called and

that's this guy here and we're going to

see this message printed out on the

terminal here let's build with gcc to

really prove this so we're going to do

the bullet is good we can clear and run

and the double end overload called

hopefully you can really see that you

can set up all kinds of crazy overloads

for your functions the next thing i want

you to see is that we can even change

the number of the parameters for example

here we can set up another guy here and

i call it max it is going to be exactly

like the one on top here for the first

two parameters but let's add a third

parameter maybe make it an end and say c

a valid overload for the max function

here so we're going to say double and

three parameters i won't go into the

details of how we can compute the

maximum between these three guys what i

really am interested in is showing you

that you can set up overloads here so

for this case we are just going to

return let's just say a this is going to

work but this is a valid overload for

the match function and it is going to

compile so let's draw and do that we're

going to pass and a double a net and the

net so we're going to pass in b which is

let's see what is called here we can

compile with gcc the border is good we

try to come up with what is going to be

printed out here what is going to be

printed okay now that you have guessed

we're going to run and we're going to

see double and ant because this is going

to call this overload again you can

overload based on the differences in the

types of the parameters that you pass

you can change the order of the

parameters like we are doing here double

end and end double or you can even

change the number of the parameters

using these techniques you can make sure

that your overloads are different in

before i close this lecture i'm going to

show you that you can also use another

string view parameters let's go down

again the name of the function is max

the return type isn't really meaningful

in making sure two functions are

different but watch the parameters we

pass here the types are string view

and we have a and b here and we are

going to compute the maximum so if we go

down here and say max and pass n hello

and world the compiler is going to try

and look for a function that takes two

character array parameters it's not

going to find it because we don't have

that guy in here but it's going to see

take something i can come up with

through implicit conversions and the

compiler is going to see that it can

a string literal to a string view type

and it is going to insert an implicit

string literal to string view and this

function here is going to be called so

we're going to put in a an output

statement here we're going to say

string view string view overload called

and if we try and run this program let's

build with gcc make sure that the build

the world is good so we can clear and

run rooster this is going to show string

view string view overload called we are

able to call this guy here and again the

message is that we really have a lot of

flexibility in how we can set up

overloads for a function in c plus plus

and please use this facility at your

advantage if this makes things better

for whatever application you are

designing i would like to welcome you in

this new chapter where we're going to be

learning about lambda functions lambda

functions are a mechanism we have in c

plus plus to set up anonymous functions

once we have anonymous function set up

we can do all kinds of crazy things with

them for example we can give them names

and code them multiple times or we can

even call them directly without even

giving them a name i realize this can be

really cryptic so we're going to head

over to the next lecture and see how we

can declare and use our lambda functions

go ahead and finish up here

and meet me there in this lecture we're

going to see how we can declare and use

our lambda functions and again lambda

functions are a mechanism we have in c

plus plus to set up anonymous functions

and an anonymous function is a function

without a name we're going to see how we

can set up an anonymous function

optionally give it a name and call it or

we can even call it directly without

giving that a name let's see how we can

do that before we talk about anything

about lambda functions we're going to

the lambda function signature and there

is a special syntax you have to follow

if you want to set up a lambda function

in c plus plus the first thing you have

to put in place is angle brackets like

this and that's going to be your capture

list we are not going to talk anymore

about this we're going to have a chance

to talk about this in detail after your

capture list which is going to leave in

this pair of angle brackets you're going

to have the parameters to your lambda

functions and this is where you can pass

arguments if you want to call your

lambda function after that you're going

to have a return type for your lambda

function but you don't have to put this

in explicitly you can live this out and

the compiler is going to deduce your

after all these things you have to put

in a pair of curly braces and inside

these curly braces we're going to have

our function body and we can do whatever

we want our lambda function to do in

this function body here after this you

will have to remember to put your

semicolon to make whatever statements

this along the function to be valid and

this is the syntax you have to follow

here we have a simple example so we have

our lambda function we want to say hello

to the console this is what we have in

the body of the lambda function but

notice that we have our capture list

delimited by these angle brackets we

have our parameter list which is going

to be empty in this moment because this

lambda function doesn't take any

parameter and we have our body which is

these two curly braces and after that we

have our semicolon to make this a valid

c plus plus statement if we try and put

this thing in our c plus plus source

this is going to be a valid lambda

function but it isn't really useful by

now because we can't call it one way we

have to call it is to give it a name and

we can give it a name by assigning our

lambda function to a variable like we

see here once we have our lambda

function declared like this this entire

thing is going to be our lambda function

type we can take this and assign that to

a variable which is going to deduce the

using auto type deduction here this is

once this thing has a name then we can

call it with the syntax we have here and

if we run this code now it is going to

print hello world to the console i

realize this syntax can be really

cryptic but if you try to remember this

you're going to find that lambda

functions are really cool and later in

the course we will see that they really

make a lot of things easier in c plus

plus so try to remember the syntax here

and everything is going to flow from

here again the syntax is to have the

capture list which is going to be the

first thing the second thing is going to

be the parameters the third thing is

going to be the return type which is

optional you can leave this out and the

compiler is going to deduce this and

after this you're going to have your

pair of curly braces and the body of our

lambda function is going to leave within

these curly braces this is the syntax

you need to remember okay we have seen

that we can give a name to our lambda

function and call it but it is also

possible to call our lambda function

directly without giving it a name and we

do that by appending a pair of curly

braces to the lambda function definition

here so we have a lambda function we

have our curly braces and we have our

parameter list we have our body here and

after the closing curly brace we're

going to add a pair of parentheses to

call this lambda function and because

this lambda function takes no parameter

we're not going to put any argument

within our parenthesis here and this is

going to call our lambda function don't

worry if you find this confusing we're

going to head over to visual studio code

in a minute and all of this is going to

make sense okay so far we haven't really

seen that we can pass parameters to our

lambda function here is a simple example

that takes parameters this is a lambda

function because it follows the syntax

for lambda functions we have

our capture list we have our parameter

list we have our curly braces and the

body is going to live inside these guys

and we are calling this lambda function

directly with this parameter list the

lambda function is going to take two

parameters of double type we're going to

print out the sum of these two numbers

and that we are going to call this

lambda function directly notice that we

literals okay this is how you can set up

a lambda function that takes parameters

and call it directly another thing we

can do is make our lambda function

return something and that's really

simple we're going to set up the lambda

function like this so it's going to take

and here you see that we are returning a

plus b and we can do that the lambda

function is now going to return

something and this entire thing we have

here is going to be a lambda expression

the lambda function is going to be

called it is going to return something

and what the lambda function returns is

going to be assigned to this result

variable here and if we print it we're

going to get the sum of whatever pass in

here printed out on the console and

you're going to see it printed out on

the terminal it is also possible to put

your lambda function directly in an

output statement i realize this can be

really confusing but please look at this

entire lambda function is same here

as a single value because this is a

lambda function that is going to return

something and what is returned by this

lambda function is going to be printed

again i realize this may be confusing to

many of you guys we are going to head

over to visual studio code in a minute

and we're going to see this and you're

going to really understand okay the last

thing we're going to look at is that we

can specify a return type to our lambda

function and the syntax to do this is to

a greater than symbol and put your type

after that and when you do that now this

lambda function is going to be forced to

return double type even if you pass it

to parameters that are not of double

type we are going to add them up and the

return type is going to be implicitly

converted to double and that's what

we're going to return and we can print

it out on the console and we're going to

see an example of this in a minute when

we hit visual studio code in fact this

is really all i had to share with you in

the slides i realized many of these

things may be confusing we are going to

head over to visual studio code and play

with these things step by step and i am

sure you're going to understand here we

are in our working directory the current

project is declaring and using lambda

functions we're going to grab our

template files and put them in place

let's do that and we're going to grab

our folder here and drag and drop it in

visual studio code and this is going to

open it it is opened here we have our

main cpp file opened we can close the

left pane here because we don't want it

anymore and we can clean up our function

here and the first thing we're going to

do is to put in the syntax for a lambda

function here and use it as a reference

as we learn about this i think this is

going to make things a little easier so

the first thing we want to do is to

declare a lambda function and the first

thing we need to put in is a capture

list a capture list is going to be in

globe in this angle bracket so this is

our empty capture list and after this

we're going to put in a parameter list

which is going to leave inside this

parenthesis here after that we're going

an optional return type for now we're

going to ignore this and after that

we're going to put in our pair of curly

braces and inside this pair of curly

braces is where the body of our lambda

function is going to leave so inside

here we can do whatever we want in the

body of this lambda function for example

we can say hello world which is

the logical thing to do at this point so

we're going to say hello world here and

we're going to put in our new line

character with endl okay now we have a

lambda function declared but we have to

put in a closing semicolon because this

is a c plus plus statement okay now we

have our lambda function declared and

this is valid c plus plus code if we're

trying to compile this program you're

going to see that it is going to compile

fine cape world finished successfully

and if we try to run it it is not going

to do a thing because we are declaring

the lambda function here but we're not

calling it to get it to do things

so let's bring up a terminal and show

you that if we run this program it is

not going to do anything so let's do

clear and run rooster you're going to

see that it's not going to print

anything and we can even go down here

and put in a closing stdc out statement

saying it done to me that we are hitting

the end of the function here without

doing anything so if we vote again the

vote is going to be good we can clear

and we're going to run rooster you see

we are printing done we are hitting the

end of the function here and are we not

seeing hello world so this function here

or this lambda function here to be exact

is not being called one way we have to

call it is to give it a name

and we have seen that to give it a name

we have to assign the entire lambda

function thing we have here to a

variable and we're going to use auto

type deduction here so we're going to

say auto func and we're going to assign

our lambda function here to this

variable and this is going to be

basically a handle we have in our

program here to the lambda function and

we can use this handle to do things with

the lambda function but by now i want

you to see that even if we run the

program now it is not going to do

anything because we're still not calling

the lambda function here let's show you

that we're going to world again and the

world is going to be good no problem we

can clear and run rooster still not

hello world because we're not calling

our lambda function to call our lambda

function we have to use our handle here

which is this variable and use regular

function called syntax so we can go down

here and say func and we can put in our

parenthesis we're not putting in any

parameter because this lambda here

doesn't take any parameters and now if

we run this program it is going to say

hello world because this line here is

going to call this lambda function let's

we're going to use gcc to build

so now if we clear and run rooster we're

going to see hello world we can call

this function multiple times because we

have a handle to it the handle is going

throughout the scope of the main

function here so we're going to go down

and call it again and if we build we're

going to build with gcc the world is

good we can clear and run rooster we're

going to say hello world twice because

we are calling our lambda function twice

this is one way we have to call our

so we're going to comment this out

because we're going to see a few other

things and on top here what we were

doing is declaring around the function

and call it through an a now we're going

to go down set up a lambda function and

call it directly without giving it a

name because that's also a possibility

in c plus plus for that we're going to

grab our lambda function here and we're

going to copy it and we're going to say

declare a lambda function and call it

direct and the syntax to do that is

you set up your lambda function like we

have seen before you see this is our

lambda function statement here but

you're going to go to the closing curly

of parentheses this is going to declare

the lambda function and call it directly

notice that we don't have a handle to

this lambda function so if you do things

like this you will have only one chance

to call the lambda function so we're

going to say hello world once because we

are declaring the lambda function and

calling it directly here and after that

we're going to say done because we're

going to be hitting the end of the main

let's build the program and show you

that we're going to build with gcc like

we always do we're going to clear

and run rooster this is going to say

hello world and we're going to be done

here because we are calling this lambda

function once again notice that now we

don't have a handle to this lambda

function so we really have one chance to

call this and you will do this if you

just want to set up some function that

you want to call directly and you don't

care about calling it ever again in your

c plus plus application and we're going

to see that we have many kinds of

problems where we want to do these kinds

okay now that you have seen this the

next thing i want to show you is how to

set up a lambda function that takes

parameters and we're going to comment

out what we have on top here because we

don't want noise output on our terminal

and we're going to grab this lambda

so let's copy it we're going to go down

here and put it in and we want to pass

two parameters now let's pass in double

parameters we're going to pass in double

a and double d you can do that

and inside the lambda function we can

print the sum of these two variables so

we're going to say a plus b for example

and we're going to print out whatever is

the result of a plus b let's do that and

after we do that you're going to see

that we get a compiler error because now

our lambda function is taking parameters

but we are calling that with an empty

so we need to give it something to sum

up let's give it 10.0 for example and a

5.0 and see what we get and after this

we need to put in our semicolon because

this is a z plus plus statement and any

c plus plus statement needs to end with

a semicolon now try to think about what

we are doing here we are setting up a

lambda function okay it's going to end

curly brace and this lambda function is

going to take two parameters of double

and inside the lambda function we are

going to print out whatever is the sum

of these two parameters that we are

after that we are calling our lambda

function with two variables 10.0 and 5.0

or i should say two double literals

that's what we are calling our lambda

function with and now if the program

runs the lambda function is going to be

called once and we're going to print out

whatever is the sum of these two numbers

and that's going to be 15. let's build

so we're going to build with gcc

the world is good we can clear and run

rooster we're going to see a plus b is

15. we are calling a lambda function

here if we put in a 50 here for example

we're going to get 60 printed out

because that's going to be our sum okay

let's boil it again and see that print

it down if we run rooster we're going to

see 60 because that's the sum of 10 and

another thing we can do is actually

not call the lambda function directly

here we can actually comment this out i

don't want to take this out because you

might want to use this as a reference so

we're going to comment this out and set

that is going to name our lambda

function and then we will have a handle

to the lambda function and we can call

so let's take out the call we are doing

here and we're going to assign our

lambda function to a variable we're

going to say auto func one we can call

this func one no problem and now

we can call this lambda function

multiple times for example we can say

funk one and pass in 10 and 20 okay and

we can say funk one and pass in five

if we run this program it is going to

print the sum of 10 and 20 and it is

going to print the sum of five and seven

and it is going to be calling this

lambda function multiple times hopefully

you can see that if you want a chance to

call your lambda function multiple times

you will need to give it a handle like

we are doing here and then you can use

multiple times and call your lambda

function however many times you want so

let's build this program and see what we

i'm going to clear and run rooster

now we're going to see a plus b it's 30

as a result of this call here and we're

as a result of this call here notice

that we are passing an integer literals

so the compiler is going to insert an

implicit conversion from and to double

because our lambda function here is

taking double type you really need to be

aware of these implicit conversions and

make sure they are working to your

advantage if they are working against

you trying to find a way to make your

code work exactly like you want because

we are learning about all these cool

tricks in c plus plus you're going to be

using them at your advantage okay

hopefully now you know how you can set

up a lambda function that takes

parameters we're going to go down and

comment this out because now we want to

see how we can return something from a

lambda function and we're going to be

using the same lambda function here so

let's grab it and we're going to say

lambda function that returns something

and we're going to set up our lambda

function here let's put that in place

and instead of printing out the sum of a

we can return that we can go in our

lambda function and say return

a plus b okay now that we have this we

can either call it directly by saying

for example 10 and 20 but now if we try

and run this code it is not going to do

this lambda function is not printing to

the concept directly it is just

returning whatever is the sum of 10 and

and if we return it we're not doing

anything with whatever is returned from

this lambda function so we're not going

to print anything and we're just going

let's boil and make you see this because

you really need to be aware of these

so the build is good we can clear and

run rooster we're going to see down our

lambda function is returning something

but we're not doing anything with the

if we want to print the return value we

need to catch it somehow and we can put

that in a variable for example we can

say auto result and assign the return

value of our lambda function to this

variable now we have a chance to print

this for example by doing sddc out

print that out and save result now if we

build this program it is going to print

whatever is the sum of 10 and 20. let's

do that and show you that this is

so world is good so we can clear and run

rooster result is 30. if we pass in 10

and 50 for example we're going to get

the same thing let's pass in 60 here

so we're going to build with gcc the

build is good we can clear pretty quick

and run rooster now the sum is 70 and

this is how you can return stuff from

your lambda function and once you return

stuff you have to be sure you cut your

results and print them out another thing

you can do is print out the result

directly after you call your lambda

function so for example we can grab this

entire lambda function thing here and

put that in an sddc out statement so

we're going to put in a second one here

and say result or we can even comment

this out we don't want to be confused

when we look at the terminology we're

going to comment out the first sddc out

statement here and we're going to say

stdendl here and put in a placeholder

for our lambda function and we're going

if we do something like this again this

entire lambda function thing is going to

return the sum and that's what we're

going to print i realize this syntax is

really cryptic but it is going to work

let's try and build our program here the

world is good so we can clear and run

rooster we're going to see that result

is 70 and this is coming from our call

here which is nested inside our htdc out

statement you can do this if you want

another thing you can do as we have seen

before is give your lambda function a

name and call it repeatedly so for

example we can try and comment out what

we have here and set up another lambda

don't want to confuse you again so we're

going to grab our lambda function here

we're going to copy it because we don't

want to type this a thousand times

and we don't want to call this lambda

function directly instead we want to

give it a name and we're going to say

aro funk 2 and we're going to assign our

lambda function type to func one

now that we have this we can say auto

and we can say func and we can pass in

whatever we want let's put in 23 and a

and this is going to add up 23 and seven

we're going to grab the result and we're

going to assign that to result one

if we go down and say auto for example

result two and say for example funk one

why not and go down and print out these

result variables we're going to see the

sums printed out and again the message

is that we can use this handle to call

our lambda function multiple times so

let's go down and print this out we're

result one and we're going to say result

one here we're going to go down and say

result two and we're going to print that

out and we can even call this lambda

function directly and put that in sddc

out here so let's say that we're going

to say result to 3 for example or direct

call i think this is descriptive enough

one the name of our lambda function or

the handle to the lambda function and we

can put in a five and a two for example

and we're going to see this print out

the result if we build our program let's

do that with gcc the bolt is going to be

good we can clear and run rooster we're

going to have result 1 is 30 which is 23

and 7 so the sum is 30. the second one

should say 54 because that's the sum and

the third one should say 7 because

that's the sum of 5 and 2 and it is what

we have here and after that we're going

to see that our program is done this is

how you can set up a lambda function

that returns something and we have seen

many ways we can work with us let's

comment this out because there is one

more thing i want you to see and that's

along the function whose return type is

specified explicitly okay we are going

to reuse the same lambda function we

have been using all along and we're

and we're going to go down and put it

down here and now we want to specify the

return type as a double the way we do

that we go after our parameter list and

we put in a dash symbol and we put in a

greater than symbol and then we're going

to specify the return type of our lambda

function let's say that we want our

return type to be ant this is how we say

it now our function here is going to

return end regardless of the types that

we put in so what the compiler is going

to do when we call this lambda function

it is going to take the parameters it is

going to add them up for example now

they are double so it's going to add a

and b as double it's going to produce a

double variable then it is going to

convert that to end and return it you

notice that now we have forced our

lambda function to really return a

before the return type was deduced from

the operation that we did here and

before we were returning double because

that's what the compiler was deducing

for a and b here to really drive the

point home let's assign this lambda

function to func one or func three let's

do that we're going to say func three

and this is a lambda function that is

going to explicitly return and and we're

going to set up another one which is

going to deduce the return type we're

the return type explicitly so we're

going to take out our return type here

and we're going to go down and say auto

result 3 and we're going to say funk 3

and add up two double variables let's

set up these variables explicitly so

that you really see what is happening so

we're going to say it a and put in

why not and let's make this guy a double

because that's what our function here

expects and we're going to do another

one do double b and we're going to put

for example and we are going to use this

variables as arguments here we're going

to say a and b and we're going to say

this should be funk 4 sorry for this

and i'm going to say result 4 and this

should say result i am making many typos

so we're going to assign our lambda

function the result of our lambda

function i should say to result for here

now we want to see the types of result 3

and result 4 here we're going to go down

and print them out we're going to say

sddc out size of this is one way we have

we're going to pass in result three

we're going to say size of result three

and we're going to go down and say size

of result for okay we have our code in

place and what we want to see

is the type that is deduced by the func

3 lambda function here we are explicitly

turning the return type into end the

parameters we pass in are going to be

double that's what we have here we are

going to add up a and b and the result

of this is also going to be double but

the compiler is going to notice that we

are returning and explicitly here and it

is going to take this double result and

transform that to end and we're going to

and we're going to get the result of

that assigned to func 3 here for the

second lambda function here we are going

to automatically deduce the return type

so what we return here is going to be

a double type and we should see a size

of it for research 3 here printed out so

we should see a 4 on my system and for

the second statement here we should see

a size of double printed out this is one

way we have to try and prove this so

let's build this program and see what we

get okay the world is good we can clear

and run rooster and we're going to see

that this is exactly what we expect here

if we want we can even print result 3

and result 4 and see what we get so

let's do that we are learning so let's

experiment with this a little bit we're

going to say result 3 and we should go

back and say result three if i can type

e and dl here and we're going to go down

and say sddc out result for okay if we

we're going to see the results printed

down the both is good we can clear and

now we have result is 10 for the

first lambda function and for the second

one result is 10.4 you can see that for

the first one the result was transformed

from double to and and for the second

one we deduced double so we still have

our decimal point here hopefully this

makes sense and this is really all we

set out to do in this lecture showing

you different ways you can set up your

lambda functions we saw the syntax of

setting up a lambda function we saw that

you can declare a lambda function and

call it through a name like func here we

went down and so that you can declare a

lambda function and call it directly

through the syntax you see here we saw

that how we could specify parameters to

our lambda function this is the syntax

and once you do this you have to

remember to call your lambda functions

with parameters like we see here we can

even use a handle given to our lambda

function and call our lambda function

multiple times after that we saw that we

could return something from a lambda

function and we had many chances to play

finished by looking how we could specify

the return type explicitly and the

syntax to do that is what you see here

we are going to stop here in this

lecture the next one we're going to see

how we can use our capture lists here

and make them do useful things

in this lecture we're going to see how

we can use capture lists in our lambda

functions and do some useful things we

have seen that the syntax of our lambda

functions includes these angle brackets

here but we haven't really used them to

do anything for what we have done in the

last lecture they were empty all the

time in this lecture we're going to use

them here is a simple example of how we

we have two variables a and b they are

of double type and they contain these

values 10 and 20. but sometimes we want

to use thanks outside the scope of the

inside the lambda function here and if

you set up your lambda function with an

empty capture list suppose you don't

and you try to use a and b like this

you're going to get a compiler error

the body of the lambda function doesn't

have access to the outer context here it

can only use things inside the lambda

functions or events that you pass to the

lambda function here but it can't

directly access things outside the

lambda functions and we can have access

to thanks that are declared and defined

outside the lambda function through our

capture list if you look here we are

saying a and b and this is the syntax we

these two variables a and b and have

access to them inside our lambda

function here and this is what capture

lists are really for giving you access

to things that are declared outside the

scope of the lambda function because if

you really think about it this lambda

function thing we have here is really a

that has these behaviors well then so

that we can call it and do things but it

doesn't really have direct access to the

where it was declared and you have to

give it access through the capture

mechanism here okay now that you know

this we're going to see different ways

we can use the capture mechanism one

thing we can do is capture by value and

if we capture by value what we're going

to have inside the lambda function is

going to be a copy suppose we have a

variable here which is c the value is

going to be 42 as you see here we're

going to set up a lambda function and

by value in this lambda function here

and what we're going to do outside the

lambda function notice the lambda

function has a handle so we can call it

we're going to loop five times

and at each iteration we're going to

call our lambda function and print the

but after that we're going to increment

our c variable and this is going to

outer variable here and what we want to

see is that the changes we are doing on

the outside here are picked up by the

inner value that we have in our lambda

function here and ahead to break it to

you this is going to not be the case

because what we have inside the lambda

function is a copy of the outside

variable here so what we're going to

have is for the outer value to go from

42 all the way to 47 we're going to go

five times incrementing this little guy

but the thing on the inside is not going

to change because it is a copy the

incrementation here is affecting the

outside variable here but it is not

affecting the copy we have inside our

lambda function so for all these loops

here we're going to see 42 print it down

and we're going to see this in a minute

when we hit visual studio code let's say

excuse my typing here okay so now you

know that we can capture by a value and

you know what this really means another

thing we can do is capture by reference

and the syntax to do that is to add an

ampersand symbol in front of the

variable that we capture here and if we

do this and run the semicolon we run in

the last lecture we're going to see now

that the changes we do on the outside

are going to be picked up by the inner

side of our lambda function because we

are capturing by reference what we have

inside our lambda function here is a

true reference to the outside the

variable here and we're going to see

that now the outside and the inside are

going to be incrementing together and

we're going to have 43 42 44 and things

like that printed out on the console

okay this is really all i have to share

with you in this lecture showing you how

you can use your capture lists and that

you can capture either by value or by

reference we're going to head over to

visual studio code and play with this a

little more okay here we are in our

working folder the current project is

capture lists we're going to grab our

template files pretty quick and we're

going to put them in place we're going

put them in the current project and

we're going to open this guy in visual

studio code by dragging and dropping in

place here and we're going to open our

main cpp file clean it up a little bit

and close the left pane here what we

want to do in here is uh learn a little

more about capture lists and we're going

to put in a piece of code to play with

just that we have two variables a and 10

here and we have our lambda function

setup and let's take out our capture

list so that you can see the compiler

if we try to use them as is here so we

have our two variables and we have a

lambda function set up here and inside

the lambda function notice that we are

trying to access the variables that have

been declared on the outside of the

lambda function here and by default if

we try to do this we're going to get a

compiler error because these two

variables don't exist in the scope of

the lambda function here let's bring up

a terminal and see what visual studio

and it is going to say an enclosing

function local variable cannot be

lambda body unless it is in the capture

list and you see that this is really

descriptive okay we have sent this error

but we want to see what the compiler

says about this we're going to pass this

through gcc and we should get a similar

error it is going to say a is not

captured and it is going to go down here

and say b is not captured here and this

is the error we are trying to use

outside variables in our lambda function

but to really do that we need to capture

and the syntax to capture our variables

is to put them inside our angle brackets

here with a comma separate to the list

of the variables that we want to capture

so we're going to say a comma b because

that's what we want to capture here and

visual studio code should be happy it is

not happy i think we need to compile

this for it to be happy so let's do that

our variables are being captured and we

are summing them up and we are printing

the result of adding them up here by

calling the function through a handle we

have set up here hopefully this is

really making sense let's build the

you're going to see that the world is

good we can clear and run rooster we

should see a plus b is 30 but the values

are getting inside the lambda function

through our capture list they are not

going through the parameter list here

this is really something you need to be

now that you know how capture lists work

let's see that you can capture either by

value or by reference and we're going to

see what that means exactly i am going

to go down here and put in a piece of

code to play with capturing by value

okay let's do that we have a variable

and we set up a lambda function which is

with this syntax here and this is the

like we did on top here so we are going

to be capturing like this and if we do

this we're going to be capturing by

value the meaning of that is that what

we have inside our lambda function is

not going to be the original value here

it is going to be a copy of what we have

what we can do here is use this thing in

a loop and really prove this

so we're going to loop five times from

zero all the way to four because this is

going to go until i is no longer less

and inside we're going to print the

outer value which is going to be

the c here after that we're going to

call our lambda function which is going

to predict the inner value in the lambda

function and we're going to see that the

incrementation we do on the outside

which is going to affect the outer value

here is going to be visible inside the

lambda function here and that's not

going to be the case the change we do

here is not going to be picked up by the

lambda function here because what we

have inside is a copy so what we're

going to see is for the outer value to

go from 42 43 43 45 and it is going to

go until we hit the end of this loop

here but the inside value is not going

to change because the change we do in

here is not going to affect the copy

that we have in our lambda function here

hopefully this makes sense and again if

you have a problem please make sure you

course platform and i will do the best i

can to help you out for now we're going

to build and run this program you see

the world is good so let's clear and run

rooster you're going to see outer value

is 43 outer value is 43 outer value is

44 outer value is 45 the outer value is

changing but the inner value is staying

hopefully this proves that the outer

value and the inner value are two

different things but we can even go

further and print the addresses of the

outer value and the inner value let's do

we're going to add that to our statement

here and say the address of this guy

so we're going to say address of outer

value or say address of inner value we

to really be descriptive in our terminal

here so we're going to say the address

and on the outer value we're going to

add another piece of information and say

address of outer value and we're going

and this is going to pick up the outer

value that we have here and this is

going to use the inner value we have in

let's try and work and hopefully these

two addresses the inner and outer

addresses are going to be different

that's what we want to see here and

really proving that what we have inside

the lambda function is a copy through

the capture mechanism so let's run the

program the world was good so the outer

value the address is the e4 the inner

value the address is de0 we are proving

that what we have inside our lambda

function is really a copy so this is how

you can capture by value and that's

going to make a copy but sometimes you

really want to capture by reference and

we're going to see how you can do that

so we're going to comment out the code

to capture by value here we're going to

grab the code and reuse it because

that's going to be very similar to what

we had before we're going to say capture

by reference we're going to put in our

code and we're going to change it a tiny

bit what we're going to do is add an

in front of our variable here that we

are capturing and we're going to say

the moment we do this what we have

inside the lambda function is no longer

a copy it's going to be a true reference

to the outer value here and now the

changes we do to our outer value are

going to be visible inside the lambda

function here and you're going to see

the addresses to be the same

let's build and really see this we're

going to use gcc to build our program

the world is good we can clear now and

run rooster and we're going to see that

the outer value let's make sure we have

some spaces after these guys and let's

go up and do that and both again because

things are really cramped together and i

so the boost is good we can clear and

so we're going to see the outer value

and the inner value are changing

together and the addresses are now the

because we have captured by reference

the inner value and the outer value are

referencing the same variable we have

outside here this is really all we set

out to do in this lecture i hope you

found it interesting the main idea was

the capture mechanism we have with our

lambda functions to capture thanks

outside the context of lambda functions

we can capture by specifying a comma

separate to the list of the variables

that we want to capture and we have the

option to either capture by value by

the variable directly in the capture

list like we do here or by prepending an

ampersand symbol here and capture by

reference and you are going to have to

choose whichever way you want to capture

your variables now that you know about

we are going to stop here in this

lecture in the next one we're going to

see how we can capture everything from

the outside context to the lambda

and meet me there in the last lecture we

saw that we could capture things outside

the context of the lambda function now

we want to see that we can capture

everything living outside the context of

the lambda function the syntax to do

that is ridiculously simple if you want

to capture everything by value you just

put an equal sign in your lambda

function capture list and if you do

something like this now you're going to

have access to everything outside the

scope of the lambda function for example

we can access the c variable here from

the lambda function but if we have any

more variables declared outside the

scope of the lambda function we will

have access to them inside our lambda

function here again this is enabled by

the syntax that we use here by putting

an equal sign inside a lambda function

notice that if you use the equal sign

like we do here we're going to be

capturing by value what we have inside

the lambda function is going to be a

copy if you don't want to capture all by

value you can capture all by reference

and again the syntax is really simple

all you have to do is put an ampersand

symbol inside your capture list the

moment you do this you're going to have

access to everything outside the context

of your lambda function but that's going

to be by reference what you have inside

the lambda function are going to be true

references to the outside variables and

you can do pretty nasty things with them

because the changes you do inside the

lambda function are going to be visible

outside the lambda function and any

change you do from the outside is also

going to be visible inside the lambda

function so if you do this make sure

this is what you want and you can use

this to your advantage okay now that you

know this we're going to head over to

visual studio code and play with us a

little more okay here we are in our

working folder the current project is

capture all lists we're going to

grab our template files pretty quick and

we're going to put them in place and

we're going to open this little guy in

visual studio code let's do that we are

going to have our folder open we can

open our main cpp file clean it up like

we always do and we're going to close

the left pane here the first thing we

want to do is to capture everything by

value and we're going to put in the code

to do that which should be very easy to

understand by now and again the syntax

to capture everything by value is by

putting an equal sign within your

capture list you have to put that within

these angle brackets and that's going to

capture everything by value now now if

we run the program we're going to see

that c has been captured by value if we

look around we're going to see that the

change but the inner value is going to

stay the same this is the same behavior

we have seen before by capturing by

value so let's build again we're going

to build with gcc the world is good we

can clear and uh bring up a terminal so

that we can clear properly so let's do

clear and run rooster now we see that

the outer value is changing but the

inner value is not changing and again

this is classic capturing by value if

you want to capture all by reference

you're going to use the ampersand symbol

here and let's do that we're going to

comment this out and we're going to take

use the code here we can do that we're

going to go down and put in a code and

say that we are capturing by reference

we should say capturing all by reference

and all we have to do to make that work

by reference is to put our ampersand

symbol within this angle brackets here

and this is going to capture everything

by reference if we run now we're going

to see that the changes we do from the

outside are going to be visible from the

let's weld with gcc and see that this is

actually the case the bolt is good as

you see here we can clear and run the

rooster we're going to see that the

outer value is 42 the outer value is

changing and the inner value is changing

as you see in our output here and this

is really how you can capture

by reference just to play with this

we're going to set up another variable

call it d and we're going to say it

contains a 5 and we can try to print

that inside our inner value here and it

is going to work you're going to see

that it has been captured we can say

sddc out inner value let's say that it

is the d variable we are trying to

access here and we're going to say d and

it is going to be visible inside our

lambda function here because it was

captured by reference here let's build

again we're going to use gcc to do that

the bolt is good we can clear and if we

run booster we should see d printed out

d and we are able to access it through

the capture mechanism and we are

capturing everything in the context by

reference here this is really all we set

out to do in this lecture i hope you

found it interesting i hate to say it

but this happens to be the last lecture

in this chapter on lambda functions we

still have a lot to learn about lambda

functions but unfortunately we don't

really have enough tools to understand

that now but for now we're going to stop

here and learn a little more things

about c plus plus then we're going to

come back and see some crazy things you

can really do with lambda functions i

would like to welcome you in this new

chapter where we're going to be learning

about function templates function

templates are a mechanism we have in c

plus to set up blueprint for functions

and have one point of control to set up

the function but the compiler is going

to generate the actual function that

gets called when it sees the function

call so this is going to solve the

problem we had before with function

overloads if you look at the code here

we have multiple overloads for the

maximum function but what we really are

doing in the body of these functions

is the same and suppose you have

12 or 13 or 20 overloads of the same

function you're going to be basically

repeating the same logic in the bodies

of this function and this code

repetition is bad function templates are

solve problems like this the way they

work you set up a blueprint for your

function and this is the syntax to do

something like that you say template

type name t here don't worry about this

syntax we're going to have a chance to

go through it in detail but if you do

things like this this is going to be a

blueprint for your maximum function and

the compiler is going to use this

blueprint to generate an actual function

when you call this function and this is

going to make things super easy i

realized some of this is really cryptic

so let's head over to the next lecture

and let you set up your very first

function template go ahead and finish up

here and meet me there in this lecture

we're going to set up our very first

function template and again function

templates are a mechanism we have in c

plus plus to avoid code repetition for

example if you are setting up function

overloads if you look here we have our

max function and we have multiple

overloads for this function we can call

it with and double and string view here

but if you look inside you see that we

really are repeating the same logic

and it is even possible to have dozens

of overloads if you want to support tons

and this code repetition is really bad

function templates are a mechanism we

have in place to avoid things like this

you set up a function blueprint using

the syntax you see here and your

function template is going to be

with this template type name teeth and

here type name t is going to be in this

and then you're going to put the

blueprint for your function t is a

placeholder for the types that you use

in your function you see that t is in

the return type here it's in the

parameters that we pass to the function

and because it is the same character

here all these things have to be of the

same type the return type the first

parameter the second parameter they have

to be of the same type okay so once you

have your function template set up like

this you're going to implement it like

we see down below here it is nothing

complicated we just set up the prototype

and inside we put our implementation you

see here we have separated this into

function declaration and function

definition but inside you see that it is

the same logic we had to compute our

maximum between these two parameters

that we pass to this function

so how does this work when the compiler

sees you call this max function for

example as we are doing here it's going

to look at the types that you pass in

are of ant type so it is going to

replace the t in here for and and it is

going to generate a function initial

and this really brings up a big point

about function templates many people

think that function templates are actual

c plus plus code they're not they're

just a blueprint from which the compiler

is going to generate the actual function

that is called by the compiler for

example when you issue a call like this

function templates are not real c plus

plus code they are just a blueprint that

the compiler uses to generate your

based on the arguments you pass to the

function when you call it so when we

issue the call like we do here an int

version of our maximum function is going

to be created so the compiler is

basically going to go in and replace n

and for t here the return type is going

to be nt the first parameter is going to

be end the second parameter is going to

be empty it's going to go in the

definition it's going to do that and

we're going to have an it function

if we issue a call with c and d like we

do here in the second line here then the

compiler is going to see that c and d

are of double type so it is going to

generate another function from this

blueprint here and it is going to

replace in double then we're going to

have another double function if we go to

the third line here we're going to do

the same we're going to call it with

strengths and it is going to generate a

stringed version of the maximum function

here so what we achieve with function

several overloads for the same function

and we have one point of control in our

code but the compiler is still going to

generate this function overloads but one

thing about this is that if a function

is not used for example if you never

call a maximum function with string

then the string version is never going

to be created the compiler is going to

generate the overloads that you only

call in your c plus plus program and

this is really all function templates

are all about they give you a mechanism

to set up a blueprint for your function

and then the compiler is going to

generate actual functions based on what

you call in your c plus plus code okay

we have saved this but i want to

function templates are just blueprints

they're not real c plus plus could and

when we hit visual studio code in a

minute we're going to see a tool

that allows us to see how the compiler

instantiates your function templates

based on the arguments you call your

function with but keep this in mind

function templates are not real c plus

plus code the rio c plus plus functions

get generated by the compiler

when you call your function and another

thing i wanted to point out is that

once a function template instance is

generated for example the interversion

of our maximum function template then if

it is needed again the compiler is not

going to generate that again it's going

to see if there is one generator already

and it is going to reuse that okay this

is really all i have to share about

function templates at this point in this

chapter for now we're going to head over

to visual studio code and play with this

a little more okay here we are in our

working directory the current project is

trying out function templates we're

going to grab our template project and

one thing i should point out here is

that our template project has been now

updated to have the launch.json file

which is going to allow us to debug our

programs so you should use a template

that includes the launch.json file here

that's going to allow us to debug your

programs and we're going to do that in a

minute when we have set up the example

here so we're going to grab our template

files and put them in place and we're

going to open this little guy in visual

studio code by dragging and dropping on

top here this is going to do our job

then we're going to open up the main cpp

file and i think we should close the

left pane here we don't need it anymore

and we're going to clean this up a

little bit so one thing i want to do is

to first do things the bad way so we're

going to set up a max function

and it's going to take end parameters

and we're going to return the maximum

between a and b and the way we do that

we say a greater than b we are going to

use our ternary operator here we're

going to put a question mark we're going

to return a or b and this is going to be

our function but suppose we need another

function that works on doubles if we put

double arguments in here the compiler is

going to insert implicit conversions

from double to end this may seem to work

but suppose you use a parameter type

that is not convertible to end for

example you use a string or something

here just for an example so we're going

and we should make these const

references because we're not interested

in modifying these strings here

and we're going to say const std string

reference a this is much better it's

going to avoid unnecessary copies of

strings and we're going to say const htd

be here then inside we're not going to

do anything different we're just going

to use the same logic okay let's do that

suppose you have another function

which takes what should i say long long

end if we need that we need to copy this

function and put that in okay we need to

do that and we're going to change this

to long long end and we're going to do

long long and our parameter and we're

going to say the same here and you see

we are setting up a lot of functions

with basically the same thing inside and

that this is a lot of code copies

suppose we have this function maybe 20

times it is possible or even worse the

logic in this function is really long

maybe 20 or 30 lines and we will have to

repeat this thing in aku so the

designers of the c plus plus language

saw this problem and they said why don't

we set up a one point of control

where we can set up our logic to do the

maximum and we let the compiler generate

functions based on the arguments we call

our functions with and they came up with

function templates and that's what we're

going to see so we're going to take out

all the other functions and we're going

to turn this maximum and function into a

function template the syntax to do that

so we're going to say template this is

what you say you put an angle bracket

and you say type name and you specify

the placeholder for the type in this

angle brackets here this is the syntax

then you have to specify your function

in terms of this placeholder t it is

going to take the place of the type so

for example here we want to return and

we're going to change this to t and the

parameters are going to be taken by

and now we have a legal c plus plus

function template it is going to take

this template here and use it to

generate actual c plus plus functions so

for example if we go in the main

function here and say ent result

equals max maximum we should say and say

x and y for example let's create these

variables on top here so we're going to

say ent x and we're going to put in a

five and we're going to create a y and

put in a seven why not now this function

is going to store the result and print

let's do that so that we can see that

this actually works so we're going to

say result and say results this is going

to do and if we build and run this

program we're going to use gcc you're

going to see that the world is going to

and uh world finished successfully we

can run this program like we always do

let's bring up a terminal and clear a

little bit and run rooster you're going

to see that we're going to see that

result now is 7 because that's the

maximum you see it is working here so

how is this mechanism working here the

compiler is basically looking in the

main function here and it is noticing

the call and it is going to look around

and see if it can find a declaration for

the maximum function here it's not going

to find it because there is none then

it's going to look at the function

templates it has in here and it's going

to see that it can do a replacement and

replacing the types that we are passing

in here so it is going to do that it is

going to take this template and it is

t by end and then it is going to

generate a function that basically looks

like what we have here we're going to

copy this and we're going to put this in

the compiler is going to take the first

t here it's going to turn that into a

net it's going to take the second one

here it's going to turn that into an end

it's going to take the third one here

and turn that into an it and we're going

to have a function definition for the

call here this is what the compiler is

one thing some of you might be thinking

is there a way to really prove this and

somebody was nice enough to design a

this function or template instances

generated by the compiler and i happen

to have that opened it is a web-based

tool so you can use this in your browser

and then we're going to grab the code we

had in our main cpp file we're going to

copy it all and we're going to go back

to our browser and remove whatever i had

in here because i don't want this

anymore and i'm going to put in my

function template if we want we can even

take this sddc out statement because we

don't want all the junk that comes with

that we are just interested in looking

generated by the compiler now that we

have the code in here we're going to see

what the compiler generates because of

the call we have here i think i could

increase the size of the font here so

can see this i think this is a little

then if you hit this play button here

let's click on it it's going to do its

processing and then the code generated

by the compiler is going to show up to

the right here you see it has detected

called the function template on line 13

here you see this line is highlighted

and then if you go to the right we're

going to see the functions generated by

the compiler so if you go here you see

of our function template and another

thing i should prove here is that

template instances that are not needed

are not going to be generated by the

compiler another way to say this the

compiler is only going to generate the

template instances it needs and again a

template instance is what you have here

the function the actual function that is

callable by the compiler generated from

your blueprint so if for example we

parameters to double let's do that okay

so we changed our types to double we're

going to hit the play button again

you're going to see that now it is going

to generate a double function here you

see that here if we change this for

what can we use let's use long long end

like we did in our lecture we can do

that we can say long long and and if we

hit the play button that's what is going

to be generated by the compiler so

hopefully this proves that the compiler

is only going to generate the instances

that are needed for the calls you do in

your c plus plus program and this is

really function templates are all about

okay now that you know this let's set up

a few more examples to see that this

so let's change the types of these guys

double let's do that and we're going to

play with this a little more in visual

studio code and let's use double

78.7 here let's do that 78.7 and we're

going to build this and one thing i

should point out is that template

instances are generated when the

compiler is doing its job and then they

in the binary representation of your

source code so the world is good as you

see here we can clear and run a rooster

we're going to see that the result is 78

and it is transformed to end because we

are assigning to end here to really get

to the correct results here we should

use auto type deduction if we do that

the compiler is going to deduce the type

of result here based on the return type

of this function or the function

template instance i should say

now we're going to change this to auto

and if we both again we should see a

double printed out correctly the both is

good we can clear and run the rooster

now we have the correct value printed

out from our function template here

let's change this to std string we can

and we're going to change these two guys

to std string why not std string x is

going to be a string electro let's use

hello for example and uh for

y we're going to say std strength and

we're going to put in a world here okay

this is going to do and you notice that

we don't even have a compiler error

visual studio code is not complaining

the compiler is going to look at the

types we call our function with then it

is going to generate is an sdd string

version of this function and what it is

going to do it's going to replace in t

and replace that for std strand we can

actually put this thing entirely in

cpp inside so let's copy this code

before we run it so that you can really

see what is happening here we're going

to take out whatever we had before we're

going to put in our code and then we're

going to hit the play button here it's

going to generate our thumb we wait for

it to do its thing and if you look here

std strength this is really a compiler

representation of std string we don't

have enough tools to really understand

this but hopefully you can see that it

with some other type we don't know yet

std basic string car it has a few things

inside that we don't really know yet we

will have to learn a few more things

about this as we progress in the course

i want to prove to you that the compiler

is doing the replacement you see t was

replaced by this thing here std basic

strength and we have angle brackets and

this entire thing is really hdd strength

in the eyes of the compiler okay now

that we know this let's go back to

visual studio code and run this we're

going to build with gcc as we always do

the world is good we can clear and run

going to see that the maximum is world

and this is going to be using the

and this is going to compare two

strengths based on this and we know that

in lexicographical order so the

comparison that is done here is

for this strength here or i should say

it is comparing things in alphabetical

order in abcde and things like that okay

now hopefully you have a big idea about

function templates they are just

to generate actual functions and this is

going to allow you to avoid multiple

function overloads as we have seen

one thing i want you to see

is that you have to be sure that the

logic you do inside your function is

supported by the types that you pass to

the function and i'm going to show you

what i mean here we're going to set up

another function template we're going to

say template type named we're going to

set up another one pedem and we're going

this however many times you want and

then we're going to set up the function

which is going to do a multiplication so

we're going to say t that's going to be

the return value and we're going to say

multiply and we're going to multiply two

parameters we're going to say t a and t

b okay and we're going to put in the

logic and we're going to just return a

multiplication operator in c plus plus

and we can use this function so for

example we can say we can comment this

out and we can set up two variables

we're going to say and x and we're going

to put in whatever we had before let's

and end to y we're going to say 7 i

think this is what we used before you

can really put in whatever you want and

now we're going to call the multiply

function template so what this is going

to do is to generate a function template

instance which is going to be of type

and it's going to do a replacement in

here and replace t with ant and then

we're going to multiply two end

parameters that are passed to this

function and we're going to return end

and if we do that we're going to get 35

printed out let's prove this we're going

to use gcc to bolt the bolt is good we

can clear and run rooster we get a 35 if

we change this to double it is going to

work so let's change this to double and

maybe put in five point one and

7.0 why not and then we're going to see

what we get we're going to build with

gcc the build is good we can clear run

but watch what happens if we try

to use the std string types okay i want

you to see that so we're going to enable

our std strength variables here

and if we try to bolt we're going to get

a compiler error but i want you to try

and guess why why do we have this

compiler if we look at what gcc is

it is saying an instantiation of our

function template required from here and

multiplication here and this is the

the compiler is going to do what it

knows to do it is going to do a

replacement in our function template and

by std strength because that's the type

we are using as an argument here the

problem is we can't really multiply two

strands if you try to multiply two

strands like we do here it's not going

to make sense what do you expect to get

if you multiply two strings it doesn't

make sense the compiler doesn't know

what to do with this operation it's

going to give you a compiler error okay

to really drive this home let's go back

and put in the code here and see what is

you should use these tools to your

advantage because they really help in

understanding what is going on so let's

hit the play button here i just put in

my code and it is going to say

compilation failed because we have the

same error cpp insights needs to compile

to give you the template instantiations

but here you see that it is basically

giving us the same error let's try and

see the entire thing here and see if we

see the real error and we can't really

scroll around with this i'm having

trouble scrolling around here i can use

these buttons i guess okay so let's see

if we see the actual error and we're not

seeing it here auto result multiply

error generated so we're going to get an

error if we try to instantiate our

template with the types that we are

passing in here which are hdd strength

cpp insights isn't really helpful here

but hopefully you understand the problem

the problem is if the compiler tries to

generate a template instance using std

strand multiplying two strands isn't

going to make sense so the compiler is

going to give you a compiler error

because this is not supported so the

message here is that you should make

sure that the template instances

generated by the compilers support

whatever operations you are doing in the

body of your function template this is

another thing i want you to see before

we close this off i'm going to take out

problematic line here and we're going to

go back to our maximum function what i

want you to see is that if you pass

different types for this function

template you're going to get a compiler

error and what do i mean by that let's

take out our std strength because it's

no longer useful for our purposes here

and we're going to just use double and 8

parameters let's use ant here

and then we call our maximum function

you see that we have a squiggly line

because the function template is forced

to use the same type for the return type

the first parameter and the second

parameter here because the placeholder

is the same so the compiler is supposed

to use the same thing for the first

argument here the second argument and

the return type that we get from this

maximum function here but the problem is

we are passing in parameters of

different types and this is going to

give us a compiler error because the

compiler want to know what to do with

the types that you pass in as arguments

and if we look at our problems tab here

visual studio code should give us an

error no match for operator uh this is

the error we had before we can try and

build again we're going to get a

compiler error again but this time it's

going to be different it's going to say

no instance of function template maximum

matches the argument list that we are

using here which is double and end

this is a problem but we will see ways

around this as we progress in the

chapter but what you should know

is that if we set up a function template

like this this is going to enforce for

all the types where we will place in t

to be the same if they're not the same

the compiler won't know how to do its

replacement and it is going to give you

a compiler error okay the last thing i

want you to see is that we can use the

debugger to debug function templates so

let's turn this back to end because we

so let's take out the decimal point here

so that we have proper intellectuals and

if we compile again this should compile

okay the world is good now what really

happens if you try to debug a program

are you going to be working on the

template instances because remember the

function templates are going to generate

function template instances with actual

types for example our template instance

here is going to have ants because we

are passing ant as argument here so how

are we exactly going to debug this let's

try this we're going to set up a break

on the call to our maximum function

and we're going to start debugging we're

and we're going to use the debugging

tools that come with gcc we have seen

how to do that in the last chapter and

we're going to start debugging let's

minimize this guy here so that we have

and we're going to run our debugger

let's maximize this a little bit

and push this a little to the left

and we're going to start debugging and

see what really happens here so we hit

the green button here we're going to

start debugging our code is building now

the binary has been passed to the

debugger and now we have hit our break

point here so let's minimize this a

little bit so that we have an easier way

to see this we have hit or break point

you see the locals are what we have in

the main function which happens to be to

the top of the call stack here

okay now we want to jump into the

maximum function and see the types that

so what we want to do here is head the

step into function and you notice it is

going to jump into our function template

here but the locals here are not giving

us the types and this is because this is

a function template it's not going to

because it's not easy to get those here

but if we look at the call stack you see

that we have information about the types

of the function that is being called we

and it is going to return and you see

that in the angle brackets here and

again this is possibly another way to

look at what template instances were

generated by the compiler because we see

the function called here is taken into

parameters and it is going to return end

let's kill our debugger because this is

really all we want to see and change the

types to double here and we're going to

see that the function to the top of the

taking double parameters so let's change

this back to five point something 5.5

maybe 7 and 0.9 why not and we're going

but uh what we really are interested in

is seeing the function template instance

generated by the compiler because of

this call here and we can do this

through the debugger this is a little

bit convoluted because you have to set

up breakpoints and whatever but it is

helpful if you don't want to use things

like cpp insights as we have seen before

and again this is also useful because

you will need to debug your code if it

is using function templates let's run

this to really prove our point here

the world is going to go through the

binary executable is going to be passed

the debugger and we're going to hit our

breakpoint here again you see our locals

are not giving us the types here but we

the function call stack to really see

this we have hit the breakpoint here at

line 15 so we can step into the call

and if we hit the body of the maximum

function here and look at the call stack

we're going to see that the parameters

we have in our function call are of

double type and again this hopefully

that the compiler has actually generated

function template instance okay since we

are debugging we can actually try and

follow this program let's hit next so

that we can hit the end of this function

finish it and hit the main function by

the moment we hit the main function

results is going to be 7.9 which is what

we have here and it is what we're going

to print we can just step over this

because we don't want to step into the

logics of sddc out so step over we're

going to print our result and our

debugging session is going to basically

end because we have hit the end of the

main function let's try and use the

compiler from microsoft to see the

information it gives us because these

things can be different depending on the

compiler and the debugging tools that

you are using we have the luxury to have

these two set up here so all we have to

do is switch the tool we want to use

here and this is going to be using the

one from microsoft if you are not on

windows or you don't want to use the

compiler from microsoft and its

debugging tools you can just use gcc and

its debugging tools here i just want you

to see different ways to do the same

things and that compilers and debuggers

can give us different information we're

going to try and debug with this so

we're going to hit the green button here

notice that this is going to be using

the compiler from microsoft if we look

at the world output here you see that we

it is what we are using to build our

binary the binary is going to be passed

to the debugger and then we're going to

hit the breakpoint here as we know

and then we're going to have our output

you see in the main function we don't

see the types of our locals why is that

i don't know why but we see the values

and if we hit the step into button to

jump into our maximum function a is

going to have this value b is going to

have this value and we look at the

template instance we can see the same

information but we are using a different

compiler this is really how you can

debug your code that uses function

templates and this is going to give us a

peek into the actual template instance

that was generated by our compiler this

is really all i had to share in this

lecture and before i let you go let's

summarize a little bit function

templates are blueprints we have seen

that the compiler is going to use those

to generate actual function template

instances real function definitions and

declarations are going to be created

when you call the function with

arguments if the template parameters are

of the same type maybe t and t then the

arguments you call the function with

must also match otherwise you'll get a

compiler error we have seen this okay

here we have a point we haven't already

covered template instances won't always

do what you want a good example is when

you call our maximum function with

pointers so let's go back and really say

because i want this to cover as much as

possible about function templates

so let's go back to our code and we're

going to modify things a little bit okay

so what we're going to do here is take

out whatever we have here we're going to

x is going to be 5 as we have seen

y is going to be seven let's use this

and then we're going to set up two

pointer variables we're going to say

px and we're going to initialize this

with the address of x nothing

sophisticated so far and we're going to

say end p y and we're going to

initialize this with the address of y we

can do this the problem is going to come

when we try to call our function here

pointers let's use px and py to call

this function and py and what this is

going to do is to generate a template

instance that takes end pointer this is

what the compiler knows to do we're

going to take the types that we pass in

here which happen to be end pointer and

we're going to change the return type to

end pointer we're going to change the

first parameter to end pointer the

second parameter to end pointer and

we're going to compute the maximum

if we compute the maximum here we're

going to be comparing pointers okay

notice this and if we try to do that we

might not get what we want because what

we get now depends on the address used

to store these guys in memory hopefully

you can see that and let's try and debug

this program so that you can really see

this we're going to use the tools from g

and we're going to try and debug it

let's do that it is going to run through

the debugger and what we're going to

have is our terminal here i think this

is not needed anymore so let's put this

to the right here and minimize a little

bit and now you notice that px contains

an address and py contains an address

hopefully you can see that in the body

of our template instance we're going to

be comparing these addresses because

we're comparing what we pass by value

here and what we pass are these two

addresses so whichever is the maximum in

these guys and i think that's going to

be dd4 here it is the maximum so

whatever is contained in px is going to

be considered the maximum let's kill

this because we have seen this

information so if we have a value in px

and that happens to be at a bigger

address it's going to be considered the

maximum let's see what we print if we

run this program we're going to build

with gcc let's do that the world is good

and run rooster now you see result is

some address because we are returning a

pointer and printing that out but we can

easily dereference this and get to the

value inside this pointer let's build

again we can clear and run rooster this

is going to give us result is 5 and

hopefully you can see that this is

really bad and not correct we are trying

to compute the maximum between x and y

and we are seeing that the maximum is

five so how can five beat the maximum

between five and seven the problem is

we're not comparing the values here we

are comparing the addresses stored in

these pointers because that's what we

are passing here hopefully you can

really see this and we can prove this

again through our debugger we can run

this through the debugger we're going to

hit the breakpoint let's minimize this

so that we can see our terminal window

here and we're going to move this around

a little bit and now we have hit our

break point if we hit next to jump into

the function you see that what we are

really comparing are a and b here and a

contains a much larger address so it is

the pointer that is going to be returned

and if we dereference that we're going

to be dereferencing the pointer that

contains this x value and the message

here is that you should be careful

that your function templates are really

what doing what you want somebody might

do this if they are not careful just

pass in pointer and expect to get the

maximum but the compiler is just going

to compare pointer addresses and you're

going to get something you probably

don't expect okay this is what is meant

by template instances won't always do

what you want a good example is when you

call a maximum function with pointers

you're going to get a wrong value

possibly there are tools like cpp

insights which can show the template in

spatial instruments we have seen that

and again the arguments passed to a

function template must support the

operations that you are doing in your

function template we have seen an

example of this by setting up a

multiplication function template and we

saw that we had a compiler error if we

try to pass std strength arguments

because we can't multiply two strings

this is really all i had to share in

this lecture i apologize it turned out

to be lengthy but i really had to put

this in one lecture so that i can really

show you different sides of the same

things we are going to stop here in this

lecture and the next one we're going to

learn about template type deduction and

go ahead and finish up here

in this lecture we're going to learn

about template type deduction and

explicit arguments what we mean by

template type deduction is the mechanism

to deduce the type it would use to

set up our template instance from the

arguments that we passed to our function

for example the compiler is going to

look at a and b here in a call to the

maximum function and it is going to

notice that they are of into type and

then it is going to say okay you are

calling your function with it types and

i see that your function templates takes

three replacers in here so i am going to

replace these guys with and and it is

going to guess that from the call that

you make here there's no other mechanism

to help the compiler out this is really

what template type deduction is about

and for the first example here we are

nt is going to be deduced for the second

function call we are passing in double

parameter so a double function template

instance is going to be generated for

the third call here we are using std

so we are going to deduce a template

instance that uses hdd string here this

is what we mean by template type

deduction but we have seen that

automatic template type deduction can

really have problems especially if you

pass parameters of different types for

example if we call a maximum function

a and c which happen to be end and

double type then we're going to have a

problem because this function template

parameters with different types because

the replacer is the same the compiler is

going to enforce that all the template

arguments are of the same type and the

template arguments are going to be what

you pass in here so a and b must be the

same if they happen to be not the same

for example ant and double you're going

now we're going to see that we can use

explicit template arguments and again i

want to make it very clear the

difference between a template parameter

and the template argument a template

parameter is what you have in your

function declaration or a definition so

what we have in our function setup here

parameters ta here and tb are template

parameters but what we have when we call

a function template is going to be

template arguments for example c and d

are template arguments and we're going

to be using this terminology in this

chapter and many more chapters to come

in this course make sure this is super

clear so what we're going to look at is

using explicit template arguments and

is a mechanism through which you can

force the compiler to use some type to

generate your template instance and the

syntax to do this is really simple it is

what we have here we say maximum and we

to use to generate our template instance

in angle brackets like we see here so

this is going to use double so this is

going to explicitly tell the compiler we

want the double version called and it's

going to generate that and that's what

is going to be called by this call we

have here a good benefit with this is

that now this is going to support

template arguments of different types so

if we make the call like this the

compiler is going to see that uh-huh we

are calling with intent double types

because a is ant and c is double

but it's going to see that you want

double template instance generated now

the compiler will have the possibility

to do implicit conversions from other

types to double and if this implicit

conversion fails then we're going to get

a compiler error so if you look here for

this is the example for that we are

passing in a and e and a is ant and e is

an std strength we cannot do an implicit

std strength to double so this is going

to give us a compiler error and this is

really all template type deduction and

explicit arguments are about we can use

these things to really make our code

easier now that you have this understood

we're going to head over to visual

studio code and play with this a little

more here we are in our working

directory the current project is

template type deductions and explicit

arguments we're going to grab our

template files pretty quick and put them

in place and after that we're going to

open this in visual studio code let's

drag and drop on top of visual studio

code here this is going to open our

folder and we can open our main cpp file

set up our function template let's clean

this up a little bit and we're going to

set up our function template let's type

this out to just to practice so we're

going to say template and we're going to

say type name and we're going to say t

and if you want you can put this on a

single line but i prefer to put this on

separate lines but let's show you that

so we're going to say t here and we're

going to say maximum and we're going to

say the parameters they are going to be

of type t and we can pass them by value

just for now and after this we're going

to go in the body of our function

template and then we can return

whichever parameter is the maximum we're

going to say a greater than b here we're

going to use our ternary operator and if

a is greater we're going to return a if

b is greater we're going to return b and

this is our function here okay now that

this function is set up let's set up a

few variables to really play with that

so we're going to include the string

library because we're going to be using

it a little bit and we're going to go

down in the main function and put in our

few variables we have a through f here a

and b are end c and d are of type double

and e and f are of type std strand the

first thing we can do we can say auto

max and we can assign whichever is the

maximum between a and b and once we do

this we're going to have that maximum

stored in max here but what i want you

to see is what the compiler does when it

sees the code like this the compiler has

to know the function template instance

it should really generate it is going to

look at the types we have here a and b

it's going to see that they are of type

and it's going to see that it can use

the function template we have here and

it's going to use that and generate a

template instance that it's going to

take and and it is going to call it to

get our maximum here again we can prove

this through the debugger we're going to

set up a breakpoint we're going to go to

our run tab here and we're going to run

we're going to build our thing and when

we hit the main function you're going to

see that a is 10 b is 23 which is what

we have here cd we have our values n and

std string because it is a compound type

or a custom type we can expand on this

and really see more information about

this but we don't have enough tools to

really understand this by now so we're

going to just to use this as a wrapper

on our stream information here now we

want to call the maximum function and

see what was generated by the compiler

and we can step into this function

because we have hit the breakpoint by

so if we hit step into we're going to

step into this function and we're going

to see that it is an int function

instance that was generated this is

if we change our call here to use c and

d we're going to generate a double

instance so let's do that we're going to

generate a double instance and if we

print this out we're going to see this

printed out but we can use the debugger

to really prove this not that we know

how to use it we don't have to look

through the terminal output window but

you can do that if you want you can set

up sddc out and print max here you're

going to see it printed out so let's run

our debugger we're going to see the

template instance that was generated

through the divider we're going to hit

the breakpoint at line 17 here

if we step inside we're going to see the

local variables for our function here a

and we're going to have the maximum

function to the top of the call stack

and you're going to see that it is a

double instance for our function

okay this is what we mean by

template type deduction it is the

that the compiler uses to know

which template instance to generate from

your function calls but as we have seen

in the last lecture this can be

one way this can be bad is if you pass

different types to the maximum function

here let's pass in a and c for example

or a and d this is going to work equally

well you see that we get a compiler

error because the compiler now it says

that we are calling with different types

but the template parameters here are

really of the same type they should be

of the same type because t is going to

be replaced for a single time so the

call we do here is going to fail and if

we run this through the compiler again

let's do that we're going to use gcc

we're going to get a compiler error and

it is going to say deduce conflicting

and then double so it can't really know

which one you want you want ent or

double the compiler doesn't know and it

is going to give us a compiler error but

now we're going to see a mechanism we

can use to make this work and that's

going to be explicit template arguments

okay what we can do to do this we can go

down and put in our call we're going to

say auto and say result or max we can

call this however we want we're going to

say the name of the function and we're

the template type that we want generated

for our function template here so if we

do something like this with double

inside angle brackets here we're going

to be basically telling the compiler

please generate a double template

instance for this call we are doing here

so if we pass in c and d for example

this is going to give us what we want

and we can print this out if we

want so let's say max okay this is going

to work if we build let's build with gcc

the build is going to be good because we

arguments and if we run this we should

see our maximum let's bring up a

terminal window and a visual studio code

here so that we can use that to see

things running we're going to clear and

run rooster you see that we have our

maximum here but using explicit template

arguments like we are doing here is

going to allow us to even pass different

types for our template arguments and for

example now we can change the first

argument here to ba which is going to be

an end and we're going to leave the

second one to bd which is of type double

now the compiler is going to see that

we're going to generate a template

instance of type double and it is going

to know that it can do implicit

conversions for the arguments we pass in

here so this is going to work if we pass

an argument that is implicitly

convertible to the type we passed in the

angle brackets here and let's debug this

again to show you that we're going to

generate a double template instance that

is going to be called and give us the

maximum that we print here so we can run

our debugger by hitting the green run

button here let's minimize this so that

our terminal window and it is down here

let's grab it and put it to the left so

that we can really see things printed

we have hit the breakpoint here and we

have our local variables you can look at

this if you want it is basically what we

have in the main function here but what

we want is to step into this maximum

the template instance that was generated

you see that it is of a double type here

okay hopefully now you can see that even

if we passed different values for our

template arguments i should say

different types because a is of type and

and d is of type double but we're not

getting a compiler error the compiler is

going to insert implicit conversions

from whatever arguments we pass here to

the explicit template argument that we

specified here again the explicit

template argument like we are doing here

using the syntax with angle brackets and

putting in our type is going to tell the

compiler please use this type and

replace that for t in our function

template here and generate a template

instance we can call to service this

call here and we're going to do implicit

and to double because that's what we

want then d is going to be of double

type we're not going to do any implicit

conversion then we're going to call this

function we're going to return a double

from it because that's our template

instance and we're going to print that

out here this is what is happening and

we can prove that a double instance was

generated through our call stack here we

see the maximum function is taking in

double parameters and it's going to

return double as our explicit

template argument here this is the

syntax that gcc uses is using but we

know now that it is a double template

instance for a function call here okay

if you're not happy with what we are

seeing with the debugger you can also

use cpp insights to really prove this

let's open this up we're going to say

let's do that and we're going to have it

open here okay we're going to

erase whatever we have in here and we're

going to put in another piece of code we

have our maximum function i should say

template function or function template

and we have alcohol here and it is

passing different types a and d remember

the last time we did something like this

by passing in different types for the

template argument this guy failed it

couldn't really generate a function

template instance because the template

parameters we have on top here specify

that these guys should be of the same

type but now we are able to use

different types as arguments because we

have an explicit argument specified

let's run this and see the template

instance that is generated and you can

see that it is of double type we

basically replaced every instance of t

here with double and this function is

going to be called to service the call

we are making here okay this is really

all we set out to do in this lecture i

hope you found it interesting the main

message was template type deduction a

default mechanism c plus plus uses to

know which template instances to

generate from your function calls but if

the defaults aren't working for you you

can use explicit template arguments to

specify the template instance you want

to generate it we are going to stop here

in this lecture in the next one we're

going to see how we can pass template

go ahead and finish up here and meet me

there in this lecture we're going to

show you that you can pass your template

type parameters by reference and we're

going to look at a simple example to

really drive this home what we have seen

so far is that we can do things like

this and specify our t like this and

this is going to generate a template

instance that passes our arguments by

value for example if we pass in double a

and double b here for our maximum we're

going to generate a template instance

which takes double as parameters and

returns a double here and this is going

to be doing things by value okay this is

what i want you to focus on right now it

is that this is going to do things by

value so if we go in our function here

and compute the maximum you're going to

see that the addresses we have on the

outside are going to be different from

the addresses we have on the inside here

if we try to print them out but you can

also pass your template parameters by

reference and the syntax to do that is

ridiculously easy you just use this like

you would use any reference we say cast

t reference here and this is going to

just replace in whatever type that you

pass when you call the function here for

example here we are passing in double

arguments so this is going to deduce a

double template instance which basically

says cost double reference maximum cost

double reference a and cost double

reference b and this is going to be the

function that is called so this is going

to really do things by reference and the

values we have inside a function

template body here are going to be true

references to the values we have on the

outside if we happen to do any

modification inside the body of the

function the modification is going to be

visible on the outside what we're going

to be doing in this lecture is just

printing the addresses here and we're

going to see that they are the same here

on the outside and inside the body of

our function template here okay this is

what we want to really play with in this

lecture but before we head over to

visual studio code i want to show you

that you can confuse your compiler if

you are not careful if you set up these

two function templates you see here

they are going to be overloads and we

can use function overloads with

templates but for now we're just going

to focus on the parameters that we are

passing in here the first one is taken

and the second one is taking thanks by

and if we issue a call like this we're

going to have the same problem we have

seen with function overloads before this

is not going to know whether you are

calling by value or by reference and

this is going to cause a compiler error

i really want you to be aware of this

okay now that you know this we're going

to head over to visual studio code and

really play with us a little more okay

here we are in our working folder the

current project is template parameters

by reference we're going to grab our

template files and put them in place so

let's do that and we are going to open

this little guy in visual studio code by

dragging and dropping here the folder is

going to open up we're going to open it

and we're going to close the left pane

here and clean up our main file here and

we are going to put in our function

template one thing i want you to see in

this lecture is that it is possible to

separate these things into function

declaration and function definition

let's just try and do that here so that

you can really see this and then you're

going to have to choose what you like a

little more so let's grab a function

header here and use that as a prototype

we're going to put that in front of the

main function and that's going to be our

declaration and if we go down after the

main function here what we have is our

definition this could work and this is

going to generate template instances for

the calls we do in the main function

here okay now that we have this we can

head in the main function and really

play with the function template here

we're going to set up two double

parameters and we're going to call the

function for example we say addon result

and we're going to call the maximum

function and we're going to pass in a

default template type deduction and it

is going to generate a double function

template instance here but what we

really want to prove is that this is

going to pass things by value and one

way we have to prove this is to bridge

the addresses both on the outside and on

the inside of the function here you see

we are already doing that in our

function template body we are going to

print the address of a so we can really

grab this and we use this stdc out

and we are going to change it to say out

here and we're going to print the

address of a let's grab this again and

use this after the function call and

is some address on the outside so for

example we may have something like zero

x and a one one one abc which is some

hex number here and that's the same

thing we're going to have on the outside

because the value we have before the

function call and the value we have

after the function call are going to be

leaving at the same address but what we

have inside the function body is going

to be a copy so it's going to live at

some other address for example let's say

and uh the main point here is that what

we have on the outside is going to be

different from what we have on the east

side and hopefully this is going to

prove that we are passing by value so

let's print out our maximum here and see

the addresses printed out we're going to

build with gcc and we're going to build

successfully we can bring up a terminal

to play with us a little more we can

clear and run rooster we're going to see

that the address on the outside ends in

dd8 and the address on the outside ends

with dd8 after the function call but

inside you see that we have a different

address and this is going to tell us

that we are passing by value and what we

have inside the body of the function is

basically a copy again i don't expect

you to see the same addresses as me here

because your operating system is going

to set up the addresses however it wants

the main point here is that the

addresses you see on the outside are

going to be different from the addresses

you see on the inside here and this

proves that we are passing by value but

what if you don't really want to pass by

value and make your function template

work by reference well we can do that we

can change our function here to do

things by reference and all we have to

is use t reference like this okay and

when we start using references we really

need to be careful and make sure people

don't modify things without our

knowledge and a good practice is to mark

your things as cost references so we're

going to do that and we are going to do

the same in our function definition so

we're going to change this to cost t

reference let's do that and let's say

cost t reference for the first parameter

here and say the same for the second

parameter here and this should be it we

shouldn't be able to use this reference

to modify the data inside the body of

the function and our function is a

little safer but what the compiler is

going to do is really what it's been

doing all along it's going to look at

the arguments that we pass to the

function call here it's going to see

that it is double and it's going to do

default template type deduction so it's

going to generate a double template

instance for the function template here

and it's going to replace in double and

we're going to have const double

reference maximum cost double reference

a constant double reference b

and we can prove this by going into cpp

insight i think we can do that so we are

here in cpp insights we can take out

whatever we had we're going to put in

to generate our instances and here we

have our template instance here

generated you see that it is going to

generate a double version of our

function template here and this is what

we have so const double reference

maximum and it is going to put in a

double explicit argument here but this

is business of the compiler what we

really care about is that it generated a

double template instance for our

function template here now if we run

this it is going to be passing

parameters by reference and what we have

on the inside should have the same

address as what we have on the outside

to really drive this home we should

our address to abc to comply with what

we have on the outside here we can try

and build our program we're going to use

the gcc to do that the build is going to

be good we're going to clear and if we

run rooster we should see the addresses

being the same out d e 0 in d e 0 and

out d e 0 and you see now we are passing

our parameters by reference and if you

want to set up a function template that

passes template parameters by reference

and i think we can also try and debug

this and see if we can see any more

information on how this works we're

going to hit our run tab here and we're

going to hit the green button to start

debugging this program we're going to be

using the debugging tools from gcc

and we see our local variables here we

have hit the breakpoint and we have the

main function to the top of the call

stack this is what we have here and if

we try and step into the maximum

function we're going to see that the

template instance now is using const

double references and this is the

template instance that was generated i

think this is all we can really see here

and let's stop this and show you one

what i'm going to show you is that you

the function template that passes by

value and the other one passing by

reference if you do that you're going to

have problems when you issue the call

like this because the compiler is going

to be confused let's change the second

one here to pass by value so we're going

to remove the cost reference here i

think it's going to do let's do that

pretty quick we'll remove the cost and

the reference we remove the cost and the

reference here and we use this guy as

our function prototype in front of the

main function here and how can we say

that we're going to go on top here and

say that okay we're going to put our

semicolon and this is going to be our

declaration but the moment we do this

you see that our compiler is going to be

confused because we have two possible

candidates for the call here it can

either be by value or by reference and

if we try to build this program we're

going to get a compiler error and it is

basically going to be saying what is

wrong here so it's going to say call

overloaded maximum double ambiguous

because we have two candidates again one

by reference one by value and this call

can be surfaced by both of these

candidates here so the compiler is going

to give us a compiler error and we have

no choice but to use either of these two

in our code and for example if we take

out the one by value here and leaving

the one by reference so let's comment

this out again if we're boiled we're

going to bolt you see the world is good

and we're going to print our data

however we have it in our code we see

the addresses are the same and another

thing i don't think i really proved to

you is that we are passing by const

reference here so the template instance

that is going to be generated is going

to be passing by const double reference

because we are passing in double

parameters but because of this cost in

front of our arguments here we want to

be able to modify the data referenced by

this name here if we go inside for

example and say plus plus a try to

modify a in any way through this

reference we're going to get a compiler

error let's work again and we're going

to see that and uh world finished with

increment of read only reference a

because we are passing by const

reference here so you should really

remember this even if we are doing the

things in the context of function

this is really all we set out to do in

this lecture showing you that you can

set up function templates that take

parameters by reference and contrasting

this with passing by value and seeing

the differences between these two things

we're going to stop here in this lecture

and the next one we're going to learn

about template spatialization

go ahead and finish up here and meet me

in this lecture we're going to learn

about template specialization and this

is a feature we have in c plus plus to

bypass the default mechanism of how

function templates work in c plus plus

okay let's make myself super clear here

we have a simple function template we

have seen a thousand times by now it is

the maximum function and it is going to

compute the maximum between a and b here

and it is going to return that it is a

function template so if we pass in a and

b which are of type and we're going to

generate a net instance of the template

here if we pass in c and d of double

time we're going to generate a double

instance of the function template here

if we pass in hdd string parameters

we're going to generate an std string

instance of this template here and this

is going to basically be comparing the

parameters we pass so we're basically

going to say if a is greater than b then

return a if a is not greater than b then

return b okay that's going to work if

what we're doing is what we have here

but the moment we pass something like

what we have here closed car pointers

then we're going to have a problem

because we're going to be calling our

function template with cost car pointer

default mechanism is going to deduce

a template instance that works on cost

car pointer arguments here and what

we're going to be comparing now are

going to be pointers to the string

rather than the string data itself and

hopefully you can see that this is going

to be a problem template specialization

is a mechanism we have to tell the

compiler for a template function

if i pass you this type please don't do

the default thing you do of replacing in

argument type for the template parameter

instead use the implementation that i am

going to give you and you tell that to

the compiler using the syntax we have

here you put a template keyword here you

put an empty pair of angle brackets and

then you specify your function the way

you want it you see it's going to return

a const card pointer the function name

is maximum which should be the same as

it's going to be specialized for const

car pointer so we specify an explicit

template argument here and then we pass

our parameters which are also of cost

card pointer and when we do this then we

can head in the body of the function and

do the comparison however we want okay

so how do we do this comparison here

here is a simple implementation of the

function template we just saw on the

previous slide you see that it really is

the same thing we have the template

keyword we have our angle brackets and

we have the function header here it's

going to return cost car pointer it's

going to be called maximum and an

explicit template argument is specified

within these angle brackets and then we

have our parameters what is really

important about this function is that

it's not going to do the comparison

we've been doing all along it's going to

and it's a c plus plus standard library

which is specialized for comparing c

strings okay if we come at cpp reference

here and look at a function called

htrcmp we have seen this before i guess

it is going to compare two null

lexicographically and you see this is

really what we want we have two const

car pointers one is going to be the

first parameter the other is going to be

the second parameter we're going to

compare them and look at the return

value we get from this function we're

going to get a negative return value if

the first parameter comes before the

second parameter in lexicographical

order we're going to get a zero if they

and we're going to get a positive value

if the first parameter comes after the

second parameter in lexicographical

order so we're going to use this

information here and compare

our two c strings here and return

something in visual studio code okay so

this is the function here it's going to

be using the logic from hdr cmp

and notice what we return we're going to

compares the greater to the other so

we're going to do strcmp we're going to

pass in our two arguments here and we're

if this returns something greater than 0

lexicographically this is the comparison

we want to do here and otherwise you're

going to return b and this is going to

compare our strings and not compare

pointers directly which is what we are

trying to avoid here and you see that

template specialization is really

helping out here now if we have this n

and the compiler sees a call like this

it's not going to compare pointers it's

going to use the template specialization

because the compiler knows that this is

fit for the call that we are doing here

because we are passing cost card

pointers this is how template

specialization works and it can really

come in handy if you are doing things

that work with pointers we are going to

head over to visual studio code and play

with this a little more okay here we are

in our working folder the current

project is template specialization we're

going to grab our template files

we're going to put them in place and

we're going to open this in visual

studio code by dragging and dropping on

top of visual studio code here this is

going to open our project and we're

going to clean it up a little bit and

we're going to close the left pane here

we don't need it anymore the first thing

we're going to do is to put in our

function template the same thing we have

been doing for a gazillion times by now

the maximum function is going to return

whichever is greater between a and b and

it is doing this by value after that

we're going to head over in the main

function and set up a piece of code to

really play with us we're going to set

up a few variables and we're going to

call our functions so we're going to say

maximum a and b this is going to return

the maximum between a and b the compiler

is going to deduce that the template

instance should be of ant type so it's

going to generate that and call it it's

going to give us the return value here

we can print it out and see it and we're

going to basically do the same

for double type and the string types

here and you're going to see that this

is going to work just fine so let's

build this we're going to use gcc to do

that the bolt is good we can clear and i

bring up a terminal to run this

and really see the output here we can

clear and run rooster you see max end is

23 because that's what we have here max

and that's what we have here and we

called max double to be of int type we

should use auto type deduction here to

because the compiler can do this better

that's what we're going to do and we're

going to deduce max sdr here and we're

going to build again let's weld with gcc

because that's my favorite compiler i'm

going to clear and run rooster now we

have correct output we have 23 which is

we have 34.7 which was deduced to be of

type double here and then we have the

maximum strength which happens to be

when comparing strengths the default is

lexicographically and what that means

the one that comes after the other in

alphabetical order is going to be

greater by that logic world is greater

than hello and it is what we are seeing

printed out here okay this is working

just fine but what if we use cost card

pointers and try to call our maximum

function template and by that i mean

doing something like this we have two

g and h which are of type cost card

pointers so they are c strings they are

going to be now terminated because we

are initializing them with a string

electron and we are comparing them here

we are saying maximum g and h and we're

going to print whichever is the maximum

after we return that from the function

when the compiler sees the call like

this it's going to do what it knows to

do it's going to replace an

scar pointer in our function template

here so it's going to return cost card

pointer it's going to pass the

parameters as coast guard pointers and

we're going to be comparing these

pointers here and we're going to return

whichever pointer is greater again here

you must be noticing the problem we're

going to return whichever pointer is

greater and we're not going to be

returning the actual string data we're

going to be returning just the address

and this can be really wrong because if

the addresses happen to be messed up

we're going to get the wrong output so

let's try and prove this again for that

i am going to comment out what we had on

top here because this could mess things

so i'm going to comment all this now and

so we're going to look at this line here

cos car pointer result and i say equals

max c mom g and h and i printed the

result here this is going to make it

easier to step into this function

without the noise from stdc out here so

we're going to set up our breakpoint

run tab and we're going to debug this

program and we're going to hit this

breakpoint here let's see the types that

we have inside our function call

so now that we are here we're going to

see that our locals are g and h and they

contain our strength if we go inside

we're going to see that g is really a

pointer to the first element in our

and h is going to be a pointer to a

that's what we have here okay

and result is going to contain some junk

data because it's not initialized yet

but we can step into this function

and see things happening a again is an

address and b is an address you see that

the debugger is really smart it's

noticing that this is a pointer to a

strength and it's going to show us the

string here but what we compare are

these two addresses and you see that b

lives in a larger address it leaves at

address that ends in 55 and a lives at

the address that ends in 50. so if we

really execute this function we're going

to return the pointer to b but you see

that b is not really the greater string

and this is really something bad you

should be aware of this this is what the

compiler is doing by default and it is

going to give us a result that is not

correct let's close this and see a way

we can solve this problem and we can use

template specialization for this what we

really need is a way to compare c

strings and not compare pointers like we

are doing here we're going to do that

using a template specialization

and the syntax for this to work you say

template and you specify an empty pair

of angle brackets and then you specify

whatever function you want to use so

we're going to go down here and specify

that we want to return the cost card

the function is going to be called

maximum we're going to specify an

explicit template argument which is of

const car pointer because we want this

template instance to work for scar

so once we have this end we're going to

specify our parameters we're going to

say cos car pointer a and cost car

pointer b and we're going to head into

the body of our function template here

now we have our two parameters and we're

going to compare them as if they were

const color strengths and we have seen

that we have a built-in facility from

the c plus plus standard library it is

this htr cmp function we can use it to

compare two strengths and we're going to

use the logic that we have here so if

the first parameter is less than the

second parameter i am talking in a

lexicographical order we're going to

return something negative if they are

equal dexicographically we're going to

first parameter is greater than the

second parameter lexicographically we're

going to return a positive value so

let's transform this logic into a

ternary operator we're going to say

return sdd str cmp we can say that and

if you have access to this function

we're going to need to include c string

let's do that we're going to include the

c string library and now we can say this

and we're going to pass in a and b and

we're going to ask ourselves is this

greater than zero okay if it's greater

than zero then if the first parameter is

greater than the second parameter let's

see graphically so we're going to return

if it's not the case we're going to

return b this is our ternary operator

here and it is going to work now that we

have this n the compiler is going to

know we have a template specialization

for a const car pointer if we call the

function like we did here calling the

maximum function the compiler is not

going to use this function template we

have on top here it's going to see that

this template specialization is better

for the cost card pointer type that we

are passing here and now if we try to

build and run the program the boat is

going to be good if we clear and run

rooster we're going to see that now the

let's see what we see if we don't have

this specialization and we're going to

comment this out because i don't think i

really showed you we're going to build

again and again if we do this

this function template is going to be

used and you know that it is going to

deduce a function that compares pointers

directly and that's going to be really

bad we can build this with gcc and

really see what we get as output we can

clear and run rooster now you see that

we are saying animal is the maximum

between these two guys but that's not

true animal is less than wild in

lexicographical order we need a way to

c strings properly and our template

is really doing that using the htd crmp

function and it is working pretty well

specialization is all about you're going

to do this if the default function

template you have is really not working

according to your needs for the type

that you want to use for this and use

this to your advantage because it's

available to you and now you know how to

use this the syntax is really simple you

say template and you say angle brackets

and then you specify whichever

implementation you want for your

specific type for example here our

specific type for which we want to

specify this function template is cost

you specify that as an explicit

template argument and then you specify

your return value your parameters and

you do whatever logic you need to do to

do things right in the body of this

template specialization here i would

like to welcome you in this new chapter

where we're going to be learning about

concepts concepts are a mechanism we can

restrictions on the template parameters

in our function templates for example we

can use this technique to say that we

want our function to be only called with

integers and if you call it with

something that isn't an integer it's

going to give you a compiler one thing i

should emphasize is that concepts are

one of the big four features in c plus

plus 20. so we're going to be learning

about this in this chapter we have just

said that we use them to place

constraints on our template parameters

but we saw that we could do something

like that in the last chapter where we

could use type trades and static

concerns for example if you look at the

function here it's going to print a

number but we have a requirement for

this number to be an integral type

through the static assert that we have

here we're going to see that we can do

something really similar with concepts

but it's going to be much cleaner and

that the logic to enforce our

constraints is not going to be in the

function body it's going to be somewhat

in the function declaration in the

constraints that we put on the template

parameter here we're going to see

specific syntaxes of how you can do this

starting in the next lecture there are

two sides to concepts in c plus plus

there are standard built-in concepts

that come with the c plus plus

programming language but if for some

reason these happen not to be enough you

can build your own and we're going to

see how we can do that later in this

chapter here are a few examples of

concepts you can use in your c plus plus

program you can use the integral

concepts to enforce that your parameters

be integrals you can use the floating

point concept to enforce that your

template parameters be of floating point

type you can do all kinds of crazy

things okay concepts are really cool and

they are going to make your function

templates much safer to work with we are

going to stop here in this lecture and

show you how you can use concepts

starting in the next lecture go ahead

and finish up here and meet me there in

this lecture we're going to learn about

concepts again concepts are a mechanism

we have in place in c plus 20 to place

constraints on our function templates

for example we can use concepts to

that we want our function template to

only be called with integers or doubles

and when somebody violates our concept

they're going to get a compiler error in

this lecture i am going to show you how

you can set up your concept and the

different syntaxes you can use and how

but before we do that please note that

there are two sides to concepts there

are concepts that are standard and built

into the c plus plus standard library

and those are ready to use and these are

what we're going to be using in this

lecture but know that you can also build

your own concepts and use them to do

whatever it is you want to do here are a

few examples of built-in concepts we can

use from the c plus plus standard

library we have for example a concept we

that people call our functions only with

integral types if they violate this

they're going to get a compiler error we

can also enforce for our template

parameters to be floating point we can

do all kinds of crazy things okay now

that you know this let's see how we can

set up a concept on our function

templates and this is the first syntax

we're going to look at all you really

have to do is to put in your template

declaration like we have been doing all

along you also have to add in the

requires keyword here after the requires

keyword you're going to specify your

concept and specify your template

parameter in angle brackets here

when you have this thing in front of

your function template like we have here

the function template can only work

right if the concept in here is

satisfied and this concept in this case

is going to be satisfied if somebody

tries to call this function template

only with integral types if they violate

that again they are going to get a

compiler error okay once we have this

concept set up we can look at the piece

of code that tries to use it and try to

guess what is going to happen here is a

piece of code we would set up in the

main function and try to call a function

template we have two variables of car

type we know that car is an integral

type so if we issue a call like this

this call is going to work the template

instance is going to be generated and

it's going to be called and give us the

results that we can print here this is

right on the second piece of code here

we have two variables of type and

we're going to call them we're going to

call our function template with and

and this is also an integral type int is

an integral type so this is going to

generate our function template instance

and we're going to call it and get the

results that we print here and if we try

to call our function template with

the concept is not going to be satisfied

and we're going to get some kind of

error and our function template instance

is not going to be generated this is

really how you can use concepts to force

some rules on users of your function

templates if i can say it like that we

have been able to do something like this

using typed traits and the static

asserts in the last chapter but concepts

are much cleaner and that they are kind

of built into the signature of your

function you don't have to go in the

body of your function and set up static

asserts the function is already

supporting concepts when you declare and

define it and this is really cool okay

this is our first syntax we can use to

for our function templates using the

requires close after our template

declaration and following that with

whatever concept we want to enforce on

our function template here please note

that you can also use type traits

in the required clause here and this is

going to work and this really says that

all you really have to put after the

is an expression that can be evaluated

at compile time but also results in a

boolean value once you satisfy these few

requirements you can really set up your

concept however you want you just have

to be careful that the expiration can be

evaluated at compile time and that it

evaluates to a boolean value and when

the expression evaluates to true the

concept is going to succeed if the

expression evaluates to false you're

going to get a compiler error because

the concept is not satisfied this is how

these things work now that we have seen

the first syntax i think it is big time

we looked at the second way you can set

up concepts and that's going to be in

your template declaration you're going

to say template put in your angle

brackets and inside instead of saying

type name t like we have been doing all

along you just specify your concept

directly and save the template parameter

like this once you do this this concept

is going to be enforced on this function

template here this is just another

syntax to really do the same thing we

also have a third syntax we can use if

we use auto to set up our function

templates and the way this works is to

just add your concept in front of the

auto keyword and once you do this the

compiler is going to enforce for the

first parameter and the second parameter

to satisfy the integral concepts so if

you have to use auto to set up function

templates this is how you can use

ways in which people use your function

we still have another way we can use

concepts in c plus plus and this is how

you do it you specify your template

declaration like we have been doing all

along you specify your function template

but after the parameter list as we see

here you're going to put your requires

close and you can put that in this place

here and it is going to work i realize

these are many syntaxes to process for

the first time but some of these

syntaxes are going to work better in

some situations and they are there just

to make it flexible for you to use

concepts in your c plus plus code okay

now that we have seen different ways we

can set up concepts for our function

templates i think this big time we

headed over to visual studio code and

tried them out okay here we are in our

working folder the current chapter is

concepts the current lecture is using

concepts we're going to grab our

template files we are going to put them

and we are going to open this thing in

visual studio code by dragging and

dropping on top of visual studio code

here we do that this is going to open

our folder we're going to open up our

main cpp file and close the sidebar here

and we're going to clean things up a

little bit and we're going to set up a

function template which is going to add

two numbers we already know how to do

that so we're going to say template type

name and it's going to have a template

parameter of t then we're going to set

up the function like we have been doing

all along we're going to say add we're

going to say t a and t b and this is

going to return the sum of a and b once

you have the function in we can go in

the main function and set up code that

would call this function and if we try

to compile this program it is going to

work now because we are not placing any

constraints on this function template

here let's try to build with gcc like we

have been doing all along you see it is

going to weld okay you see the world is

good world finished successfully and if

we want we can run this application and

it is going to print result a

result b let's take this out because we

haven't done this yet but it's not going

to print result c but if we want we can

really print it it's going to work so

put that in and we're going to say

result c and print result c here and

world again let's world now to take this

world is good we can bring up a terminal

to try this out and we can clear and run

rooster now you see result a is 30

because that's the sum of a and b here

result b should be 16 which is what we

have result c is 13 which is what we

should get by adding these two double

now we wanted to constrain this function

to only work if somebody passes integral

types and when we put that constraint in

place it is going to work if we add up

two character variables because they are

integral types it's going to work if we

add up two integer variables because

they are integral types but once we hit

with the double variables we should get

a compiler error because the constraint

is not satisfied let's do that we're

going to comment the double thing first

because we want to really isolate it and

see it and see the compiler error that

we get and we're going to add a

constraint to our function template

using concepts okay if you want to use

concepts in c plus plus 20 the first

thing you need to do is to include the

library that gives us access to concepts

and we're going to do that by saying

include concepts this is easy now that

we have this end we're going to use the

first syntax we saw in the slides and

we're going to add the requires close

after the template declaration

and we're going to say std integral and

we're going to say the template

parameter here i think this is the

syntax okay watch what happens if we do

this down in the code we are calling the

integer types so this is going to

compile fine because the concept here

is satisfied this concept is going to

enforce for the template parameters we

call a function template with to be

integral types let's build and see if we

get to compile successfully you see both

finished good everything is going to

work and if we run our program we should

see results a and result to be printed

out let's run the program we see our

result here now we're going to comment

out the others and leave in the double

example and we're going to uncomment

that and i want you to see the problem

our function template with double

variables here you see visual studio

code is already complaining it is saying

there is something wrong if we look at

the problems tab is going to say no

instance of function template add

matches the argument list but this is

really not descriptive enough but the

problem is our concept is not satisfied

by calling our function template with

double types because we clearly said

that we want the function to only be

called with integral types let's build

our program we're going to pass this

and we're going to get a compiler error

that says that some concept was

and we see we see in function main

use of function t add with double with

unsatisfied constraints and this is

really clear when we see an error like

this we will go and look at the

constraints that the function has and

we're going to see if we satisfied those

like we did in the main function here

and we will know that the function

doesn't support non-integral types and

we will fix this problem this is really

in writing safer function templates now

that we have seen the first syntax i

think it is big time we looked at the

other syntaxes so let's do that let's

copy the code here because we're going

to be reusing this a couple of times and

adapt it instead of typing this entire

thing the second syntax involves getting

rid of the requires close all together

and just using the concept instead of

type name here so i'm going to say std

integral and this is going to be enough

this is going to tell the compiler to

enforce this concept for this function

for all the template parameters that go

in the place of t here i hope this makes

sense now if we go back we see that we

still have our squiggly lines here if we

try to compile we will get the same

compiler error okay and you see we have

the same compiler error function add t

called with unsatisfied constraints i

think if you go down we're going to see

even more stuff out of this it's going

to say required the satisfaction of std

integral with t but now we are trying to

call this with double so this is really

going to lead to a compiler error so

this is the second syntax and it is

going to do the same thing now that we

have seen this we also have a third way

we can do this and that's through the

auto mechanism let's set up a function

using auto so we're going to say auto

add auto a and auto b we have seen that

we can do that in the last chapter and

we're going to return a and b a plus b i

should say if we do this you see that

the squiggly line goes away and we can

add these things up and print the result

the return type is going to be deduced

by the compiler automatically but know

that this is going to generate a

function template behind the scenes this

is just a nicer syntax we have to use

auto to set up functions that work for

multiple types let's build and uh see

how gcc handles this the world is good

because we have no constraints here and

if we run our program it's going to work

it's going to give us 13 as the sum of

11.1 and 1.9 but we can also place

constraints on this function here and

you do that by specifying your concept

in front of the auto keyword here so for

example we can say std integral and std

integral fold the second parameter here

let's say that and once we do this if we

go down we should see our squiggly line

on the call of the function here because

now the way we are calling this function

is not valid the function clearly says

that it wants to be called only with

arguments that satisfy this concept here

if we're trying to build again with gcc

we're going to get the semicompiler

error let's do that and it's going to

unsatisfied constraints the same error

and if we go down we should see that it

concept to be satisfied here so this is

the third syntax you can use if you

happen to be using the auto syntax for

your function templates let's comment

this out because we still have another

syntax we need to learn about this is

going to be our syntax three and we're

going to comment this out and the last

just leaving in our function template

let's copy this because i don't want to

type this again we're going to go down

and say syntax form and put in our

function template we're going to take

this requires close we're going to cut

it out and we're going to put it after

like this and this is going to be valid

syntax to enforce a concept on your

function template if we go down you see

we have this wiggly line and i should

prove that this works with other

integral types here let's just comment

out the double line here and uncomment

the other we had for car and ant if we

try to build this program now it is

going to work fine because the

constraints are satisfied but the moment

we uncomment the calls with double types

we're going to get a squiggly line which

is a good warning that we have a problem

but if we ignore the squiggly lines

and adjust build with gcc we're going to

get the same compiler error and it's

going to say that to call our function

the integral concept for the arguments

that we pass here and the double

arguments we're passing in here are

violating our concept so we get a

compiler error this is really how you

can use concepts in c plus plus i tried

and came up with simple examples to show

you different syntaxes you can use

and this is really it try to get

yourself familiar with these syntaxes

and it's not going to be really hard to

use concepts in your c plus plus

programs okay this is really all i had

to share in terms of the syntaxes you

can use with c plus plus 20 concepts if

you go to the documentation you're going

to have more information about this but

we're going to do a few more lectures to

really drive this dancehall for now you

can come to cpp reference here and see

more concepts that you can use we have a

lot of this and we can really use this

to tune our function templates however

we want okay for example you see our

integral concepts you see a floating

point concepts and there are even more

classes but we haven't learned about

classes yet and we will do that starting

at the next chapter but now i just want

you to be familiar with concepts that

were introduced in c plus plus 20. and

here is another piece of documentation

you can look at just to complement what

we are talking about in this chapter but

i wouldn't recommend reading this just

yet because it's just going to confuse

you there is a lot of things we still

need to learn to really be able to

understand this so try to go through

this chapter and i am going to try and

break this down in ways that you can

understand this the main message is that

there are more concepts here you can try

in your c plus plus code if it makes

sense for the problem you are trying to

solve with c plus plus we are going to

stop here in this lecture in the next

one we're going to show you how you can

set up your own concepts in c plus plus

go ahead and finish up here and meet me

there in this lecture we're going to see

how you can build your own concepts and

this is going to bring us into the

second part of concepts we can use in c

plus plus in the last lecture we used

the concepts from the standard library

that are built into the c plus plus

programming language starting in c plus

plus 20. in this one we're going to be

building our own concepts and without

waiting anymore let's see how you can do

that and this is the syntax you can use

to do that and it is really simple the

way you do that you say a template

declaration specifying the template

parameter you want to constrain and then

you say concept you say the keyword

concept you give your concept a name you

put the equal sign after that and then

you're going to specify the requirements

for your concept so for example here we

are using a type trait to specify that

this type trait is going to determine

what works for this concept here and

what this is going to do is to enforce

for our template parameter to only be

integral if it's not integral we're

going to get a compiler error and one

thing i should tell you is that the std

integral concept is exactly built like

this in the c plus plus standard library

this is really cool so if you want to

set up your own concept and you want to

do that using typed traits you can do

that like this and it is going to

enforce for your template parameters to

satisfy that typed rate or to be exact

this concept is going to be satisfied

when the type trait evaluates to true if

the typed rate evaluates to false at

compile time the concept is not going to

be satisfied that's another way to look

at that down here we have another syntax

we can use if we have multiple

statements in our concept all you have

to do is specify the concept keyword you

give it a name you go to the equal sign

and then you add a requires close the

requires close is going to specify the

template parameters for which you want

to enforce your concept and then you're

going to put a pair of curly braces and

inside that you're going to specify the

syntax you want your concept to satisfy

for the two parameters to be

supporting the multiplication operator

if this multiplication operator is not

supported for the template parameters

that we passed the concept is going to

fail and again i should emphasize that

this doesn't check for the value of a

multiplied by b it's just going to

enforce from the syntax to be supported

so for example if you call a function

template with this concept and you try

to pass in integers it's going to work

because you can multiply integers but if

you pass two strings this is going to

fail because it doesn't really make

sense to multiply strings okay this is

the syntax now we only have one

statement to enforce inside but if you

want you can even put more statements if

you go down here we have another example

called incrementable this is going to

require for the template parameter to be

incrementable we specify the concept key

world we say the concept name we put in

our equal sign and then we say requires

we put on template parameter and put in

our requirements for any template

parameter that is using this concept the

syntax here must make sense so you must

be able to take the value that you get

from here and for example say i plus

equals one this is going to be valid

syntax you're going to say plus plus a

and plus plus b all these are going to

be valid c plus plus syntaxes for the

template parameter that you try to call

this function template with and if this

doesn't work you're going to get a

compiler error because your template

argument isn't really satisfying this

concept so this is really how you can

set up your own concepts in c plus plus

once you have your own concepts set up

you can use them like we have been using

the other concept from the ziploc plus

standard library for example we can use

syntax one to put a requires clues and

say that we want to satisfy our own

concept with this particular syntax you

will have to put in these angle brackets

and put your template parameter inside

this is the syntax you have to use you

can also use syntax 2 and specify my

integral directly in this angle brackets

in your template declaration and this is

also going to work we can even use this

with the auto syntax for our function

templates it is going to work okay now

that you have sent this i think it is

time we headed over to visual studio

code and play with us a little more okay

here we are in our working folder the

current project is building your own

concepts we're going to grab our

template files like we always do and

we're going to put them in place and

we're going to open this thing in visual

studio code let's do that we have our

project open here or folder i should say

we're going to clean this up a little

bit and we're going to include our

concepts library and we wanted to set up

our own concept the first syntax we're

going to see is by using type trades and

we're going to say template type name t

and we're going to say this concept we

want this template parameter to satisfy

we're going to say concept and we're

going to say my integral which is going

to be the name of our concept we're

going to put an ecosign and then we're

std integral v and specify that we want

this type trait to be satisfied for this

concept here and after this we need to

put in our semicolon and i think we need

to include the type traits library

because we are using that we should say

std is integral so sorry for this and

this is going to work now okay now that

we have the concept set up we can use it

like we have been using other concept

for example we can set up a function

which is going to add up two numbers and

it is going to use this concept here we

have multiple syntaxes we can use so

let's go down and try this out we're

going to say template and say type name

t and we're going to require this

concept to be satisfied for our function

template we saw that we could use the

requires close here and say my integral

and say the template parameter we want

to enforce this on and after this we're

going to just put in our function

template we're going to say add what we

have been doing all along in the last

lecture we're going to say t a

and t b and we're going to return a plus

b now this function is going to support

our concept let's go down and set up two

variables we're going to say and x

and we're going to say 6 for example and

into y and i'm going to make this a 7

why not and we're going to say add

x and y once we do this you see that we

have no problem because the concept is

satisfied for the arguments that we are

passing in here the concept is satisfied

because the type trait here is going to

return true for this type here because

it is an integral type when the type

trait returns true then the concept is

going to be satisfied if the type trait

returns false the concept is going to

fail let's try and bolt and really drive

this home you see that the world is good

our function is working so the function

template and stands for this code here

is going to be successfully generated

and we're going to call it when the

now let's change the type of these guys

to double and try to violate our concept

and make it fail once we do this you see

the call here has a squiggly line and a

visual studio code is not going to say

that it is a concept problem which is a

shame but we can still run this through

the compiler and the compiler is going

to tell us what is wrong so it's going

to say use of function add with

unsatisfied constraints and if we go

down we're going to see the exact

constraints we violated and we're going

to say required for the satisfaction of

my integral with t we are calling this

with double and double is going to

evaluate this to false hopefully you can

see that you can really set up your own

concepts using the syntax here and we

can use our concept with all the

syntaxes we have seen in the last

lecture so for example we can take out

the requires close all together here and

template declaration here so we're going

to say my integral and if we do this

we're going to fail again because the

concept is not going to be satisfied

we're going to have the same problem we

can change the syntax to use the auto

syntax but before we do that let's

change this back to type name t and then

put our requires close after the

parameter list of our function template

and we're going to say my integral and

specify the template parameter and this

is a valid function template with a

concept applied to app and if we both

again we're going to get the same

compiler error so you see the same error

and we can use the auto syntax let's do

that we're going to take out the

template declaration here we're going to

take out the requires close here and

we're going to change our t to auto and

the way we do that we're going to say

std no no std we are using our own

concept so we're going to say my

integral auto this is going to work and

we're going to say my integral auto and

my integral auto here the moment we do

this you see that we have squiggly lines

here because our concept is violated but

if we're trying to build again we're

going to use gcc to do that the build is

going to fail you see that the same

concept is violated and we are able to

use our concept throughout the four

syntaxes that we saw in the last lecture

and this is really cool now that we have

this we're going to comment this out and

we're going to see that we can set up

concepts that have requirements spanning

multiple statements or multiple lines

okay let's go down and do that suppose

we want to set up a concept that is

going to enforce for the templates

parameters to be multipliable

with the multiplication operator we have

here we can use this syntax here we're

going to put in our template declaration

we're going to say concept we're going

to say the concept name we're going to

put in an equal sign and then we're

going to put in a requires close

with our template parameters and and

after that we're going to put a pair of

curly braces and inside the curlies

we're going to put the requirements for

example in this case we require for the

template parameter here to support the

multiplication operator between two of

these types if the multiplication

operator is not supported we're going to

have a problem and that this is the

concept that is going to enforce that

one thing you should know is that this

that multiplying a and b is valid syntax

it's not going to check the value of a

multiplied by b and you should really

understand this now that we have this n

we can set up a function to use these

two guys why not use the function we

have seen before to add two numbers

let's do that and we're going to put in

our requires close and we're going to

require now to support the multipliable

concept and we're going to specify our

template parameter we have the concept n

so we can use that to do whatever we

want now we're going to say t

add and we're going to say t a and t b

and we're going to return a plus b this

is the same function we've been using

all along okay now we have our concept

in place and we have a function template

that is going to use this concept

let's see if we can add up x and y and

see what we get we're going to world

with gcc we're going to see that the

world is going to be good because our

concept here is satisfied we are passing

double types for our function template

and it is legal to multiply two double

variables if we multiply two doubles

we're going to get a value and that's

going to be valid c plus plus syntax but

let's see what happens if we try to

change our arguments to hdd strength

let's do that so we're going to say x is

hello and we're going to say why is

world why not let's go down and put in a

semicolon and the moment we do that you

see that we have a problem and visual

studio code is not good at this yet

and run this through gcc we're going to

get that our concept is violated let's

look at the compiler error here it's

going to say constraints not satisfied

and it's going to tell us that we are

calling the add function with the values

that can't be multiplied it's going to

say the required expression here is

invalid and this is how you can set up a

concept like this and you can really use

put constraints however you want on your

function templates but here we have just

used one statement inside our concept

here we can even put in more so to drive

this home we're going to set up another

concept let's go down and put that in

place the concept is going to be called

incremental it's going to be using the

same syntax we saw here but we're going

to be putting a requirement on the

template parameter here to support

incrementation and we want for every

type that goes in the place of t here we

must be able to say a plus equals one

this must be valid c plus plus syntax we

must be able to say plus plus a this

must be valid c plus plus syntax and we

must be able to say a plus plus this

must be valid c plus plus syntax

now that we have this we can change our

add function to use this concept why not

we're going to say incrementable and now

this function is going to be required to

use things that we can increment on and

you see it is failing already because we

can't really increment strengths what

does that even mean so let's build and

show you the compiler error okay you see

incremental is not satisfied and that

the required expressions aren't valid

you see plus plus a is not valid a plus

plus is not valid and a plus equals one

should not also be valid but we're not

seeing that here but hopefully you see

the message here that our concept is

failing here if we comment out our

strengths here and uncomment double all

these operations we have here are

supported for the double type

so we should not fail here if we try to

compile this because the concept is

compiler to build you see the build is

and we can clear and we can bring up a

terminal to really see this that our

binary was generated let's do the ir

we're going to see our rooster

executable here and if we go down let's

say done we're going to see that if we

build again to bring this in

consideration clear run rooster the

program was generated and it is really

running because the concept here

with our call using double arguments

here okay so this is really all i set

out to share with you guys in this

lecture i hope you know the syntaxes you

can use to create your own concepts you

can either use type traits like we have

seen here and the syntax is to put the

keyword concept put in your concept name

put an ecosign and then specify your

type trait here this is going to work if

you need something a little more

complicated then you're going to use

requirements for your concept in these

curly braces you can either put one

statement like we did here or you can

even put as many statements as you want

just remember to end them with

semicolons and another thing you

shouldn't really take lightly is that

this is just going to check for syntax

it's not going to check for the value

you get after you add one to a here for

example it's not going to check for the

value you get after you multiply b it's

just going to see that a multiply b

is valid syntax for the types that our

template parameter is using here we are

going to stop here in this lecture this

one we're going to zoom in a little more

on the requires close here go ahead and

and meet me there in this lecture we're

going to learn about some more things we

can do with our requires close but

before we do that let's look at the

kinds of requirements we can put in our

requires close the first one is a simple

requirement which is what we have seen

so far we can also do a nested

requirement and we're going to learn

about this in a minute and we can do a

compound requirement which is going to

allow us to specify more things about

what we require for our concept there

are also type requirements but these are

really advanced for the scope of this

course so we're not going to talk about

these in this course what we're going to

look at are these three first here so

let's look at a simple requirement this

is what we have seen already here we

have our template declaration we have a

concept declared the concept name is

tiny type we're going to put in our

requires close we're going to put in our

parameter list and we're going to put in

our curly braces inside the requires

close we have a statement here which is

going to enforce that size of t is less

and what this really means it's going to

check that size of t the syntax here is

correct and this can really throw people

off i have said this in the last lecture

but i set up this little example to

really drive this home and show you that

if you are not careful your concepts are

going to be really wrong this is going

to check for the syntax so for example

if we call a function template with this

the concept is going to be satisfied

even if the size of the car is less than

4 obviously but that's not going to be

the job of this concept here this

concept is not going to enforce for the

expression here to evaluate to true it's

going to just check the syntax and if

you pass something smaller than a net in

a function template with this concept

this is going to be valid c plus plus

syntax so the concept is going to work

so now you must be asking how can i

enforce for the value of this expression

using concept well for that you will

have to use nested requirements and a

nested requirement is going to have

another requires keyword inserted in

front of it now if you use the syntax

like this now this is going to check

that size of t is actually less than 4.

if it's not less than 4 this is going to

return false here and the concept is

going to fail and this is how you can

use nested requirements to enforce for

some expressions to be true in your

requires close another kind of

requirement you can set up for your

concept is the compound requirement and

this is going to allow you to check if

something doesn't throw an exception you

can do that using the no accept keyword

but we're not going to use this now

because this is not in scope for what we

can do at this point in the course but

you can also check the return type of an

expression and divorce that it satisfies

some type trait for example so here we

are saying for our concept and if we

pass in two parameters the syntax for

adding a and b must be correct and

supported for those types but the result

of a and b must also be convertible to

ant and you can do something like this

and this is going to work you can

enforce these kinds of things using

compound requirements okay now that you

know about these kinds of requirements

you can put in your requires close let's

head over to visual studio code and play

with us a little more okay here we are

in our working folder the current

project is zooming in on requires close

we're going to grab our template files

and we're going to put them in place and

we're going to open that in visual

studio code pretty quick by dragging and

dropping here this is going to open up

our folder we're going to do the usual

we're going to close the pane here we're

going to clean things up a little bit

and we're going to include our concepts

library let's do that we are going to

set up a simple concept we're going to

say template and we're going to say what

the concept is the concept is going to

be called the tiny type and we're going

what makes this concept a tiny time

we're going to put in our requires close

and we're going to put in the template

parameter call it t why not and we're

going to put in our closing semicolon

here now what is going to make this

concept a tiny type is that the size of

the template parameter view is going to

be less than four let's suppose we are

doing the function and we wanted to use

integral types that are smaller than

four bytes in memory suppose you want to

in the problem that you are trying to

solve in c plus plus the way we can

enforce this we can say size of t is

supposed to be less than four let's say

size of properly can't type can i okay

the moment we do this you're going to

see that this is valid c plus plus

syntax so we're not going to have any

squiggly lines but what you should know

is that this is a simple requirement in

c plus plus concepts and what this is

it's just going to enforce the syntax of

what we do here what we put here must be

valid c plus plus syntax so only

enforces syntax this is what you should

really remember okay now that we have

this end let's try it out and show you

some problems you can really run into

we're going to set up two character

variables we're going to call the first

one x we're going to initialize this

with 57 why not 67 and we're going to

put in the other variable which is going

to be y and it's going to have a 56 n

you can put in whatever you want just

make sure that you are within the range

of the card type which is between 0 and

255 if you remember okay now that we

have this n i realize we don't have a

function we can try this on let's set up

another function pretty quick we're

going to say tiny type auto we can do

that you already know this syntax and

we're going to say add tiny type auto a

and a tiny type auto p we can do that

and we're going to return a plus b now

that we have this let's say a and b down

here and call this function we're going

to say x and y and we're going to try

and compile this program and it is going

to compile fine because the type we are

using to call the function which is car

its size is going to be less than four

okay so this is going to work and it is

let's build with gcc you're going to see

that the build is good let's try and uh

change the type here to end or even

double you know double is 8 bytes in

memory so we expect this to probably

give us something wrong double type is

eight bytes in memory so we expect the

to be false because the size of t is

going to be eight and eight is not less

than four this is going to be false so

some might expect this concept here to

but let's try and really prove you wrong

we're going to build with gcc and you

see it's building successfully what this

is really doing is that with simple

requirements like we have here c plus

plus is only going to enforce for this

to be valid c plus plus syntax and size

is going to be valid c plus plus syntax

even if this expression here evaluates

to false this is not going to enforce

for the value of this expression to be

false you can't do that with simple

requirements what you will do is check

that this is valid syntax now what do we

do if we really want to enforce that

less than four if you want that you

should use nested requirements and the

syntax to do that is really simple we

can go down here and put that in we're

going to say requires we're going to add

a requires keyword in front of this then

we're going to put our expression here

let's copy it and put it in i don't want

to type this again the moment we do this

now compilation is going to fail if we

pass a type whose size is not less than

and let's try and build again you're

going to see that the world is going to

fail now and we're going to have a

failed concept and you see world

finished with errors we have constraints

not satisfied and if we go down here

we're going to see required for the

satisfaction of tiny type auto and we

passed in a double type whose size is 8

bytes in memory and it is less than four

bytes you see the requirement here it is

not satisfied we can do this using

nested requirements okay if we go down

for example and change this to car some

people call this char but i call this

car that's my habit if we change this to

and try to bolt again you're going to

see that it is going to weld fine

because now what is wrong here let's see

what we got wrong huh we are getting a

compiler error here what is the problem

let's go up and try to analyze this a

little bit it's saying deduce the return

type does not satisfy placeholder

and we are requiring for the return type

of this guy to be tiny time uh-huh i

think i know what the problem is the

problem is the arithmetic operations

like the addition we're doing here are

not supported for types which are

smaller than ant and is the smallest

type we can use with arithmetic

operations so what the compiler is going

to do is going to do implicit

conversions from car to end and inside

here what we will have are going to be

ant the result of this is going to be

ant and the return type is going to be

is going to violate the requirement we

have here which is saying that the size

of tiny type here should be less than

four and the return of ant is not less

than four so we can try and fix this by

putting an equal sign here and i think

it's going to work let's do that and

world again this is a good learning

experience and now you see that the

build is going to work because now the

return type is going to satisfy our

requirements so let's prove that we are

getting a net out of this actually we're

going to do our own result and we're

going to say equal and grab the result

of this guy we should really prove these

thanks and after this we're going to

print the results we can do that and we

can even go further and print the size

of result here so we're going to say

size of result okay now that we have

this end we can weld with gcc and the

world is good don't mind this squiggly

line it is probably visual studio code

messing with us you see that the world

is good we can now bring up a terminal

and run this and see the size of the

return type and really prove

that the compiler turned that into an

end even if we called our function with

car arguments this is interesting so

clear and run rooster now we're going to

see results is going to be 123 and the

size of the result is for even if we

passed in car types as our arguments

okay so hopefully this proves that you

can set up nested requirements to

enforce for the expression here to be

checked another type of requirement you

can do is a compound requirement let's

put this in and we're going to put in a

simple example to drive this home i

think i should take this function and

put that below our concepts so a

compound requirement looks like this you

put your expression in acrylics like

this and then you can even put

requirements on the values of the

expression for example we can enforce

that the value of a plus b here should

be convertible to and if it's not

convertible to end the concept here is

going to fail this is a compound

requirement you can even put no except

keywords in here but we're not going to

go this far because we haven't really

learned about exceptions so for now i'm

going to test this out i just wanted you

to be aware that you can do that now

that we have this concept n let's play

with it and see how we can make it break

thanks we're going to change our concept

to edible let's say edible here and

we're going to say edible and we're

put in our car types here and it is

we can add two car variables and this is

going to work because we can add two car

variables and this is valid syntax what

we're going to get out of that is going

to be an ant because remember the

compiler is going to insert implicit

conversions from card to end because it

can't really add two card types and is

the smallest thing you can do arithmetic

operations on so the result of this is

going to be an end so a lens is

convertible to an edge this is going to

work let's build and show you that this

is going to work we're going to weld

this with the gcc you see build is good

we can try and run this and see what we

get after calling the function we get

result is 123 and this is going to be

the size of four because we get a net

out of this let's try and change this to

double and see what we get so double

let's say double here and if we would we

expect this to work because adding up

two doubles is going to give you a

and we're going to return a double from

and uh a double is convertible to a net

so we're going to return a double from

this guy and this should say eight now

because that's what we are returning

from the function here let's build with

gcc you see the both is good we can

clear and run rooster this is going to

say size of result is eight because now

what we are returning is going to be a

double from this function here and

double satisfies our concept adding up

two doubles is valid syntax and what we

get out of that is going to be a double

and a double is convertible to a net

this is going to work let's try and

change our parameters here to strength

we're going to comment out our x and y

variables here and we're going to set up

two strings going to say std string x

and we're going to say hello and you

know what we're going to say and why

we're going to say std strength y

and we're going to say world why not and

the moment we do this you see that we

have a problem why do we have a problem

because it is now a requirement for the

result of a and b to be convertible to

end remember that you can add up two

strands for example you can say auto s

and say x plus y this is going to work

because you can add up two strings and

this is going to concatenate them so

this is valid syntax why are we failing

here because we have a requirement for

this to be convertible to an end and the

strength isn't really convertible to an

end so this is going to fail let's build

this program and show you that this is

actually the case we're going to see

world finished with arrows and let's see

the error we have okay so constraints

not satisfied it's going to say required

the satisfaction of audible with auto

here in requirement and it's going to

a plus b does not satisfy the type

requirement because what we get after

adding a and b is not convertible to an

a plus b convertible to an end this is

going to fail okay so let's try and

remove this requirement to convert to

end and see that this actually works

we're going to remove this i'm going to

and try to build again i am going to use

gcc to build and now you see that this

is welding because we no longer

have the requirement of the return value

of this expression or result i should

say the result of this function

now doesn't have to be convertible to an

okay let's put this back because i want

you to see this later as a reference and

now you know how you can use compound

requirements to really put constraints

on your function templates this is

really all we set out to do in this

lecture i hope you found it interesting

i think i should comment out these guys

because i don't like to leave you with

code that has compiler errors let's turn

this back to double so that this works

we're going to weld again okay the world

is good and we are going to stop here in

this lecture in the next one we're going

to see how we can combine concepts and

go ahead and finish up here and meet me

there in this lecture we're going to see

how we can combine concepts using

logical operators we can combine

concepts using the and operator and the

r operator as you see here let's look at

a simple example here we have a concept

it is time type we have seen before and

it's going to check that the size of the

template parameter we pass is less than

four it's going to enforce the syntax

with a simple requirement but it's also

going to enforce for the value of this

expression to be true if the value is

not true the concept is going to fail

and we are using a nested requirement

for this so this is our concept here

let's try and set up a function and see

how we can combine this concept with

other concepts here we have a function

it is going to return a t the name of

the function is func it is taking in our

parameter and here we have the body of

the function within these two curly

braces but what we have here is a

concept we want to apply to this

function here and the first line here is

going to show that we can combine the

like we do here so this entire thing is

going to be a logical combination of

concepts so we can require that the

template parameter be either an integral

type or a floating point type using the

or operator here another thing we can do

is use the and operator as you see down

here in the second line and we're going

template parameter is both integral and

a tiny type and the compiler is going to

enforce these things as we are about to

see in a minute when we hit visual

studio code you can even specify your

concepts in place for example the third

line here is going to say we require for

the concept to be integral so it should

be an integral type and we're going to

specify our tiny type concept in place

you see we are doing that right here in

the function declaration and this is

going to work this is a valid c plus

plus syntax but i don't recommend this

because this is going to make your

function declarations really ugly so now

that you know this we're going to head

over to visual studio code and play with

this a little more it's just using the

or and and operator to combine concepts

okay here we are in our working folder

the current project is combining

concepts we're going to grab our

template files pretty quick and put them

in place and we're going to open this in

visual studio code as we always do by

dragging and dropping here we have our

file we're going to open that up and

close the left pane here i don't like it

and we're going to include our concepts

library let's do that we have this and

the first thing we're going to do is to

put in our tiny type concept here so it

is tiny type it's going to require that

the syntax for the size of t less than

4b supported this is a simple

requirement again and we're going to

require that this expression be true and

using a nested requirement okay now that

we have this concept we can combine this

with other concepts let's use the same

function we've been using all along so

we're going to say template type name

team and we're going to put in our

requires clause so we're going to say

requires we can use std intergroup and

and say or it should be htd floating

point i think we have this end this is a

concept we have which is built into the

c plus plus standard library we can use

this now that we have this we can then

say the signature of a function t x is

going to add up t a and t b and it's

going to return the sum of a and b now

you can only call this function with

either integers or floating points if

you try to deviate from this the concept

is going to fail and we're going to get

a compiler error let's go down and try

this out we're going to say and x and

put in a 6 for example and into y and

put in a 4 and we're going to add this

up we're going to say add x and y and if

we do this this is going to work because

this is an integer so the concept here

is going to succeed let's weld with gcc

and show you that the build is good the

world is good so no problem we can

change this to double it is going to

work because double is a floating point

let's say double properly and if we blow

it again the bullet is going to go

through but if we try and use for

example a strength let's say std

strength string that's a strength and

we're going to change this into double

quotes we can do that and say std

strength and i put this in quotes again

double quotes okay if we do this you see

we have a squiggly line and if we walk

we're going to have violated our concept

because the parameters that we pass

don't satisfy this concept it's neither

an integral type or a floating point

type and if we go up here we're going to

see that we have violated a concept

constraint not satisfied and it's going

to say the concept that was not

satisfied here which is right here okay

you can combine two concepts using the

or operator but we can also use the and

let's go down and try and put up a

simple example that is going to do that

now what we're going to require for

people to use this function is to

both tiny type and integral so we're

going to say requires std integral i

think we have this n and we're going to

tiny time and we're going to say our

template parameter here the moment we do

this and let's turn this back to being

at let's say ant x and put in a seven

what we had before and at y and let's

say four or a five doesn't matter

let's see our thing again so tiny type

requires for the size to be less or

to four so ant is going to work this is

going to build because the concept is

going to be satisfied it is both

let's work and see this run you see the

world is good our concept is satisfied

but the moment we try and use something

we're going to have a problem

let's use a double for example we're

going to change this to double and world

we expect compilation to fail because

the type which is double doesn't satisfy

the tiny type concept and we're going to

see that here okay so we're going to see

weld finished with arrows and we're

going to have a lengthy error here but

the meat of this is that we have a

constraint which is not satisfied

that for required for the satisfaction

of std integral so double is not going

to satisfy this i think double was a

really bad example because it's not

integral so integral is going to fail

what if we pass in long ant okay which

an integral type but it's not going to

satisfy tiny type so let's say long end

and we're going to build now we are

going to violate let's use long long ant

because i think long end is not large

enough so we're going to build now we're

going to fail because tiny type is not

satisfied you see required for a

dissatisfaction of tiny type and it's

going to say size of t is less than 4 is

not satisfied because guess what the

size of lung lung ant is greater than 4.

you can try and prove that by taking out

this guy here and saying stdc out size

of a long long end we're going to see

and if we're boiled now we're not going

to violate our concepts because we're

the word is going to be good what we

want to do is run the program and see

the size of lung lung ant we can do this

rooster eight the size of lung lung ant

is eight and it is going to violate our

tiny type concept okay you can do things

like this and combine the concepts but

we can even put our concepts in place we

can do something crazy and for example

say let's copy this and we're going to

go down and say requires integral but

we're going to put timely type in place

for example we're going to grab the

requires close here and copy it

and put that in place of tiny type here

and you're going to see that this is

going to be valid c plus plus syntax if

we take out the semicolon because it

shouldn't be there but look at this this

is really ugly this is going to make

your functions really hard to read but

it is going to work exactly the same way

it did if we call this function we're

going to violate tiny type let's do that

we're going to build with gcc we have an

error let's bring this up so that we can

see what is wrong nested requirement

size of t is not satisfied this is a

syntax you can use but i don't really

recommend this because this is going to

make you code hard to read and this is

really all we set out to do in this

lecture looking at how we can combine

our concepts using the and operator and

the or operator and you can really use

this in all the syntaxes for concepts we

have seen but i just used this in this

lecture because it is simpler to show

we are going to stop here in this

lecture the next one we're going to look

at concepts and auto go ahead and finish

up here and meet me there in this

lecture we're going to zoom in on

concepts and the auto key world we have

already seen that we can do something

like this use the auto keywords with our

functions and let the compiler generate

a function template behind the scenes

and this worked pretty well we could use

this syntax to put constraints on our

other keywords and we saw that the

compiler could actually enforce this and

throw a compiler error if our concept

here is violated what i haven't shown

you is that you can even enforce

concepts on variables that you declare

you can do something like this set up a

variable say auto x and call the

variable x and enforce for the variable

to be an integral type i don't really

think you have much use for this because

once you call the function and assign a

value to a variable you already have an

idea of what is going to come out of the

function but if you have a use case for

something like this please go ahead and

use this it is going to enforce your

concepts you can even use concepts like

this set up a variable and assign a

literal to the variable name using the

auto keyword here but i personally find

this useless because you are putting in

why do you want to put a protection if

you know that you are putting in a

double literal then the variable should

be a double type i find this a little

bit useless but it is supported in c

plus plus if you have a use case for

this please go ahead and use this now

that you know this we're going to head

over to visual studio code and play with

us a little more okay here we are in our

working folder the current project is

concepts and auto we're going to grab

our template files and we're going to

put them in place and we're going to

open this up in visual studio code let's

do that pretty quick we're going to have

our folder open we're going to open the

main cpp file close the left pane and

clean things up a little bit and we're

going to include our concepts library

and we're going to put in our function

which is going to be using the auto

really make the syntax nice and cool but

we're going to be constraining our auto

parameters here to use integral types if

we call this function with something

that is not an integer or any trigger

type really we're going to get a

compiler error so if we go down here for

example and say add and say

10.9 and 0.1 we're going to get a

compiler error because 10.9 and 0.1 are

double literals and we only support

integral types in this function here so

let's work and show you the error but

you must know this by now because we

have done this like a gazillion times

the concept integral is going to be

violated and it's going to say required

for the satisfaction of integral so the

concept is failing here we're going to

get a compiler error but if we change

this for example to 10 and 5 put in

whatever you want which is an integer

this is going to work we're going to

you see the wealth is good so you can

use auto with concepts like this we have

seen this syntax already a couple of

times in this chapter what we haven't

seen is that for example you can set up

a variable in main and call this x y

naught and say this variable should

satisfy the concept and specify the

concept you want for example let's say

std integral and if you do something

like this let's see what we get from

this we're going to world you see the

work is good because if we add up these

guys we're going to generate an integer

instance for this function and we're

going to deduce the return type as ant

so the return type is going to be

integral and it's going to be assignable

in our variable here but if we change to

floating point i think we have this

concept in place yes we do but it is

going to fail because what we get from

this function is going to be an integer

and we can't assign to this because this

what you try to assign to this variable

here should be a floating point this is

the meaning here and if we do this we're

going to get to the error probably so we

have the arrow and it's going to say

constraint not satisfied and it is going

constraint we didn't satisfy which is

its floating point here this is how you

can put constraints on your variables

even when you are declaring them so

another thing we can try here is to

a literal to this variable here let's

put in a 3.9 and see if this actually

you see the build is good and the

requirement is for what we assigned to

this variable here should be a double

and a 3.9 is already a double so no

problem but if we try and make this

this is going to fail so let's build

again you see the concept is going to

fail and this is how you can use these

things to constrain your variables i

personally find this a little bit

useless at least in this case here

because i know that i have an integer

and i am assigning this to a variable

why do i need the help of concepts to

constrain my variable here but in the

case where you are calling a function

for example using a 5 and an 8

this can come in handy because it's not

easy to keep track of the return type

you get from a function because the

function might have a return expression

that has multiple different variables

and it's not easy to keep track of what

you get back from a function and you can

use a constraint like this to make sure

what you get from the function is what

you want and if it's not what you want

you're going to throw a compiler error

because the concept you use is going to

fail i would like to welcome you in this

new chapter where we're going to be

learning about classes classes are a

mechanism we have in c plus plus to

build our own types and use them like we

have been using other bulletin types

like and to double or whatever and we're

going to be able to do that by setting

up blueprints of our class types and

we're going to be using those blueprints

to build actual objects that we can use

in our c plus plus program so for

example we can have a class as a

blueprint and we can create real class

objects in our c plus plus program as we

need them and we're going to be learning

all about this in the next few chapters

we are going to head over in the next

lecture and let you set up your very

first c plus plus class go ahead and

finish up here and meet me there in this

lecture you are going to build your

first c plus plus class classes are a

mechanism we have in c plus plus to be

able to build our own types if you

remember so far in this course we have

been using basic types like ant and

and we were using them like this we said

the type of the variable we give the

name of the variable and then we

initialize this variable and we can use

this throughout our program now we are

at a point where we need to start

designing our own types suppose we want

to build our own type that models a

person for example suppose a person is

the age and the address and we want to

and use them as players for example and

when we have the properties of a person

we can do all kinds of crazy things with

them we can make them jump up for

example if we are designing a game we

can make them run we can make them fly

we can do all kinds of crazy things in

this lecture we're going to use a

cylinder as an example and we're going

to model a cylinder in our c plus plus

program a cylinder is defined by two

things it has a base radius which is

modeled by this r you see here and it

and when we have this information about

our cylinder we can really do all kinds

of crazy things for example we can

compute its area the base area and the

r squared this is a formula you get from

your basic mathematics education

you can compute the volume of the

cylinder and the formula to do that is

area multiplied by the height and we can

really do all kinds of crazy things with

the cylinder if we have this information

so we're going to use this information

and model a cylinder we can use in our c

plus plus program and we're going to be

using classes to do that the syntax to

set up your class in c plus plus it's

really simple you say class this is the

keyword you have to put in here you say

the name of your class in this case it

is cylander as you see here and then we

put a pair of curly braces in place the

start is on top here and the end is down

here and after your class definition

you're going to put a semicolon inside

the class we really have two parts we

have member variables which are going to

model the properties that your class is

going to have in this case we have two

properties that really define a cylinder

we have the best radius and we have the

height we have decided to model these

things as double types inside our class

and this is going to make the first part

of our class the member variables the

second part is going to be made of

behaviors or functions that do things on

the class using the properties and one

function we have is the volume function

which is going to help us compute the

volume of our cylinder here if you look

at its syntax it really is a function we

have a return type we have the name of

the function we have the parameter list

which is empty by now and we have our

curly braces that delimit the body of

our function inside the function we're

going to do nothing special we're just

going to return the volume of our

function here and if you remember the

multiplied by the height and this thing

here is going to model the base area you

multiplied by the square of the radius

and then we're going to multiply this by

the height and we're going to return the

volume for use by whoever is calling

one thing we haven't really talked about

is this public thing you see here

and what this says is that the members

that we have in this class are going to

be accessible from the outside of the

class for now we can't really understand

this but when we hit visual studio code

i'm going to show you what this exactly

now that we have the class declared we

can really use it like we use any other

types in c plus plus for example we can

and set up a variable called cylinder

one as you see here is type is going to

be cylinder and notice that this is

really a type that we build ourselves

and we can really use it like we use

other variables for example we can call

it function using the syntax here and

print the volume this is going to print

the volume using the volume function

that we just set up in a minute if we go

down we can modify things about our

cylinder for example we can use the dot

notation here to change the base radius

and change the height and if we try to

print the volume again this information

is going to be picked up and be used by

the volume function to compute the

volume of our cylinder here this is

really cool if you want you can also set

up another cylinder like we do here and

we're going to print the volume and we

can really do all kinds of crazy things

with our types like this okay this is

our class and we can really use it to do

a lot before we head over to visual

studio code and play with us i want to

bring to your attention that members of

are private by default and what i mean

by that is that for example if we don't

put this public keywords in here we want

to use the volume function for example

like we have used it in our main

if the member is private it won't be

usable outside the class this is what we

mean here we are trying to use this

member in the main function

outside the class definition it won't be

accessible if it is private and we make

it public by putting the public keyword

and the column like we do here

everything after this public keyword is

going to be public until we change this

to private somewhere in our program if

we need that now that you have an idea

about how you can declare and use your

class in c plus plus let's head over to

visual studio code and play with us a

little more okay here we are in our

working folder the current project is

your first class you are going to build

your very first class in c plus plus

we're going to grab our template files

we're going to copy them and put them in

place and then we're going to open this

little guy in visual studio code by

dragging and dropping here this is going

to open our folder we're going to close

the left pane here and clean things up a

little bit the first thing we want to do

but before we do that we're going to

need the pi variable because remember

for use in computing the area and the

volume of our cylinder that we want to

model like we did in the slides so the

way we're going to do that i am going to

declare a const variable and i am going

and i am going to initialize this with

pi to get pi i'm going to cheat a little

bit i'm going to go in my calculator and

let's see if i can get pi here and i

click on this and i'm going to grab pi

here and copy it this is the easiest way

i can find so i'm going to put it in

here and this is going to be our

variable now that we have this we're

going to set up our class and that to

define a class you say class you have to

put in this keyword and then we're going

to say the name of the class the name of

the class is going to be cylinder and

after we do this we're going to put a

pair of curly braces and we're going to

end this with a semi-colon you have to

remember this if you don't put it here

the ziploc plus compiler is going to

now that we have the class blueprint

here we're going to put in our member

variable and these are going to be the

variables we use to model the base

radius and the height of our cylinder

we're going to put in a double variable

and we're going to call this base radius

and we're going to brace initialize this

to zero we can do this and we're going

to set up another one and call it height

and we're going to also initialize this

to zero okay now that we have this we're

going to put functions or methods in our

class and we do that by just putting the

function definition in our class so our

function is going to be returning double

because it's going to be returning the

of our cylinder so it's going to return

double here the name is going to be

volume and it's going to be computing

the volume and returning that remember

the formula to compute the volume

is going to be pi we have a pi variable

on top and we're going to multiply by

this radius twice because the base

radius has to be squared let's do that

and multiply by base radius again and

then we're going to multiply by height

and notice that these are guys declared

in the body of the class if i can say

that this is the definition of the class

we are able to use this guys because we

are inside this class here okay now that

we have this our class is really defined

but we can't really use it quite yet

what do i mean by that let's go in the

main function and we're going to set up

a variable of type cylinder we can do

that and let's call this cylinder one if

we do this and try to compile this this

is going to work fine let's do that

world finished successfully this is

welding but we have a function called

volume here and we can try and call it

using the dot notation that we saw in

the slides let's try and print the

volume of our cylinder here and see what

we get so we're going to say volume we

can save that and we're going to say

cylinder one and do volume okay let's

see if we can call this function here

and the moment we do that you see that

we have a squiggly line here so visual

studio code has detected that something

is wrong let's hit the problems tab here

and see what we get it's going to say

expected an identifier on line what this

uh we put three columns here let's

and the error is going to change to be

suddenly the volume declared at line 6

is inaccessible from this location here

this is what the error says and it is

because members of the class are private

by default so they want to be accessible

from the outside of the class like we

are doing in the main function here

notice that we are able to access them

from the inside of the class you see

base radius is declared down here and we

are able to use in the function because

the function volume here is inside the

class so the members are accessible even

if they are private but private members

can't be accessible from the outside of

the class like we are doing in the main

function here that's why we have this

problem let's see what the compiler says

we're going to pass this through gcc and

we're going to get a compiler error that

we expect and the compiler is really

specific on this it's going to say

double cylinder volume the volume

function from the cylinder class is

private within this context and which

context the line 19 when we are trying

to use it in the main function so if you

really want thanks inside the class to

be accessible from the outside you need

to make them public and change them from

private how do we do that it is really

simple you use the syntax we saw in the

slides we're going to say public and put

a column here and when you do this it is

advised to align your things a little

bit properly so when we do this

everything after this public keyword is

going to be public in this class and it

will be accessible from the outside

let's try and build now but before we

build let's show you that the squiggly

line should be gone visual studio code

is still confused let's try and vault

let's pass this through gcc now you see

that the world is good okay now if you

try and print the volume here we're

going to get zero because the base

radius is braced initialized to zero the

height is zero and if we multiply like

this we're going to get a zero and

return that let's try and run this

program because we just build it

successfully we can bring up a terminal

to do that and let's clear and run

rooster and we can see that the volume

is zero and it is what we expect okay

now our class is working but there is

really something bad about it and

that is because the public keyword is

going to make everything public in this

class the member variables are also

going to be public so we can go down

here and print the base radius and the

height for example let's do that and

show you that this is the case so we're

going to say cylinder one and say base

radius this is going to print and we're

going to say hi we're going to print

this out if we try and print these guys

let's build and pass this through gcc

you see the bolt is good and if we clear

and run rooster we're going to see that

this radius and height are or accessible

to show you that this can also be

different from zero let's change the

base radius to one and the height to one

to make it a unit cylinder let's try and

weld we're going to change these guys to

one and the volume is going to be

3.14 or something let's run rooster

we're going to see our volume here and

we have the base radius and the height

but this is really bad design because

in most cases you're going to want to

keep them private from the outside

because users of your class don't really

care about the member variables they

just want to do things with your class

for example calling the volume function

here so what we usually do in

practice is to flag our member variables

as private and we can do that using the

private keyword as we do here and at the

moment we do this everything after this

private keyword is going to be private

to the class it is only going to be

accessible from the inside of the class

but if we try to access that from the

outside we're going to get the same

compiler error we saw before when we

tried to access private stuff from the

class in the main function here visual

studio code is going to give us a

problem saying that these member

variables are not accessible from this

context here and if we pass this through

gcc we're going to get a clear compiler

error saying that the height

base radius are now private in the class

and we can't access them from the

outside this is really what i wanted you

to see and this is good design okay now

that we have our class declared and that

we can use it in the main function i

want you to see that it is possible to

change these member variables but to do

that we will need to turn this back to

public and we're going to see a better

way to do this later but for now let's

make them public and show you that we

can change things around and make our

cylinders a little more interesting so

now that they are public we can go in

the main function and do crazy things

change the data for example we can

change our member variables to be

something else let's go down and say

cylinder one and say base radius we can

use the dot notation and put an ecosign

and give another value to our base

radius let's make it 10 for example and

change the height to be something else

we can change that and we're going to

put in a 3 for example why not now if we

print the volume again we're going to

get another value let's copy this and

our changes here and if we build the

program it should well define the world

so we can hit enter and clear and if we

run rooster we're going to get

3.14 first here the first line here and

the second line is going to give us

another volume and if we multiply these

and if we use our formula to compute the

volume we're going to basically get the

same thing let's try and prove this with

our calculator we have it around so we

have pi in here we're going to multiply

the radius squared we're going to put

100 here and we're going to multiply

this with 3 which is our height let's

942.47 which is what we have here

roughly the same thing so you see that

our function is really computing our

volume we can even go down and change

the height to something else for example

we're going to change the height to

let's make an eight and i printed the

volume again you can keep playing with

that our volume function is computing

our volume using the data that we have

in the member variables this is the

message here let's build again the world

should be good we're going to clear and

run rooster now we see another

number for our volume and this is really

how you can declare a class again you

use the syntax you see here class you

say the class name you put a pair of

curly braces and you put your semicolon

members of your class are private by

default but you can make them public if

you want using the public keyword as we

did here inside your class you're going

to have two parts you're going to have

the member variables which are going to

be properties that define what your

class is and we're going to have

functions or methods let's say that and

these are going to be behaviors

of your class you're going to go through

these functions to make your classes do

things and once you have the class

definition in place you can use it to

variables as we do in the main function

here and the variables we create from

our class are usually called objects in

c plus plus terminology okay the class

is really a blueprint and we create

objects using that blueprint and objects

are going to have runtime data that we

store in our class okay so for example

if we hit this point here the base

radius is going to be 10 and the height

is going to be eight and that's going to

be runtime information for our class

object stored in this variable that we

call cylinder one here this is really

what i wanted you to see okay let's try

and recap what we know about classes so

far a class can have member variables

but so far we have used member variables

as stack variables if we go back for

example you see that we say base radius

here you notice it is not a pointer or a

reference or anything it is a stack

variable inside our class so member

variables can only be stack variables

like we have here but they can also be

pointers but they can never be

references and the reason is a reference

can never be left uninitialized and in

the classes when we declare member

variables the ability to leave them

uninitialized is really important and we

can't really do that with references i

can't really go into the details of that

as we will see that as we progress in

the chapter but know that member

variables can either be stacked

variables or pointers but they can never

be references in z plus okay that's what

we just said here members can't be

references classes can have functions or

methods that let them do things we saw

an example of this with our volume

function class methods have access to

the member variables regardless of

whether they are public or private we

have seen that the volume function will

have access to our member variables

regardless of whether it is public or

private and last but not least private

members of classes aren't accessible

from the outside as we saw in the main

function you can't access them from the

main function you can only do that from

the class definition itself this is

really all i had to share in this

lecture i hope you found it interesting

we are going to stop here in this one in

the next one we're going to see how

from constructors go ahead and finish up

here and meet me there in this lecture

we're going to learn about constructors

and constructors are special class

that are called by the compiler to

construct your class objects and they

are special because they have no return

type a constructor can never have a

return type as you see here they have

the same name as the class so for

example for our class in the last

lecture that was called silenter the

constructors are also going to have the

same name as the class they are going to

be called also slander constructors can

have parameters but if it makes sense

for whatever it is you are trying to do

you can also leave the parameters out

and constructors are usually used to

initialize the member variables and put

them in a state where you want them in

let's look at how you can declare

constructors for your classes

here is our cylinder class you see we

have our member variables we had they

a public section which is going to have

our functions or behaviors as you see

here the member variables are what we

have seen from the last lecture but if

you look here we have a few new things

we have two things that look like

functions but they don't have return

values that's something you should

they have a parameter list as you see

here and we have a pair of curly braces

because these are really functions and

these are special functions that are

going to be called by the compiler to

initialize your class objects if you

look here in this example we are

constructor with no parameters to

initialize our member variables to 2 and

we have another constructor as you see

down here which is going to take

parameters directly and it's going to

take the radius parameter and the height

parameter the parameters are of double

type because that's what we expect in

our class and we are passing them by

value here because they are fundamental

types and we don't really mind copying

them but please keep in mind that they

are going to be passed by value and what

you have inside your constructor body

are going to be copies of the original

arguments that were passed to your

constructor and this is really how you

declare constructors for your c plus

plus classes constructors can either

have parameters like we have again on

this example here or they can have no

parameters and this is going to be a

default constructor we're going to see

that this is going to be called when you

variables of this cylinder type without

passing the parenthesis like we do when

we call this second constructor here

we're going to see this in a minute okay

this is all i think i have to share in

the slides about how you declare

constructors let's head over to visual

studio code and play with this a little

more okay here we are in our working

folder the current project is

constructors we're going to put in our

template files pretty quick let's do

that and we are going to open this in

visual studio code by dragging and

this is going to open our folder let's

and we're going to take out what we

don't need in the main function and on

top here and i am going to reuse code

from the last lecture because we don't

want to type that again so let's put in

our class definition we have our

variable pi which is going to be used to

compute the volume in the class here and

we have member variables okay now that

we are here let's change the member

variables to be private because making

them public is really going to be bad

design it's going to expose them in the

main function and people can mess with

them and really change the logic of how

our class works without our concept it

is advised to make your member variables

private unless you really have a

compelling reasons to make them public

okay now that we have our class here

let's set up constructors for it so

we're going to go down here in the

public scope and say constructors and

we're going to set up the first

constructor which is not going to take

any parameter so we're going to say the

name of the class remember a constructor

doesn't have a return type and it has to

have the same name as the class so we

need to comply with that and we're going

to put our pair of curly braces and

inside we're going to initialize our

member variables however we want so what

we're going to do here we're going to

set the base radius to something let's

make it a 2 like we saw in the slides no

problem with that and we're going to set

the height to something else and we are

going to set the height to 2 as well we

can do that you can use what you want

and now we have our constructor and it

is initializing our thanks okay now that

we have the constructor in place

how is it really called by the compiler

and notice that our constructor is in

the public scope of the class

if it isn't public you want to be able

to access it from the outside and the

compiler will fail to build your objects

and we're going to see this in a minute

but before we do that let's try and

create a cylinder object now so we're

going to say cylinder and say cylinder

one like we did in the last lecture

and when we do this notice what we see

if we print the volume of our cylinder

object here this is an object because

we're creating this from our blueprint

which is the class definition here you

really need to know this this is a class

object let's say that and we're going to

print its volume we're going to say

cylinder one and we're going to call our

volume method we should say and if we

build you're going to see that this is

the volume is not going to be coming

from the initial values we have here we

will have changed these guys to 2

from our constructor here because the

compiler is going to look at this line

here and see that we are trying to build

a silent object it's going to look at

the class definition and it is going to

say do i have any constructor

that i can use to build an object from

the syntax i see here and it's going to

see that it has a constructor that

doesn't take any parameter and it's

going to use it to build our object and

it's going to be using this information

to build our cylinder object so the base

radius is going to be two the height is

going to be two and it's going to use

that we print here you really need to

if gcc accepts this you see the both is

good now we can bring up a terminal and

clear and run rooster you're going to

see that we have 25 something which is a

result of using this information we have

here if we take pi multiplied by this

base radius multiply by this base radius

again and multiply by height we're going

to get this here you can try this out it

is going to be what you see here and

this hopefully proves that the compiler

is using our constructor here but we can

let's set up a breakpoint here

and we're going to run this through our

debugger we can come back to the run tab

and we're going to try and use the

with the gcc compiler that's what we can

use if you are on windows you can also

tools that come with the compiler from

microsoft but we're not going to use

that now gcc is going to be fine we're

going to start the debugging and we

should hit our breakpoint when the build

is done let's wait a minute okay we have

we can minimize this a little bit and i

show the terminal to the right here i

think we can do that let's do that let's

put that a little bit to the right here

and minimize a little bit okay we have

our thunk in place we have hit our break

point you see these are the local

variables we have here we have a

cylinder object which is not initialized

yet because you see what we have inside

is really junk data we haven't put in

anything yet but now that we are at this

break point here we can hit step into

and step into the code that constructs

our cylinder object because at this

point liner 25 here hasn't run yet so

we're going to step into and you're

going to see that we hit the constructor

this again proves that our constructor

is being used to build our cylinder

now we can move to the next line we're

going to set up the base radius and if

we hit next here this is going to set

and you see that height is in one

because we haven't set it up yet but if

we execute this line you're going to see

that height is also going to change to

and now if we hit next we're going to

get out of our constructor and our

cylinder object will be already

constructed if we look again here we're

going to see that radius is 2 height is

2 and we can print the volume and if we

hit step over we're going to see our

volume printed out here hopefully again

this proves that our constructor here is

objects and it is doing that because it

is the syntax here we don't pass any

parameter to our cylinder object as we

created so this must be calling the

default constructor which doesn't take

any parameter this is the message here

let's close our debugging session and

maximize our visual studio code instance

because we're going to set up another

constructor which is going to take

parameters now and you have seen the

syntax to do that in the slides it is

nothing complicated we're going to say

the name of the constructor which is

going to be the name of the class and

and say rad param for radius and we're

height and we're going to make this

double and after that we're going to

head in the body of our constructor and

we're going to initialize our guides to

the parameters that will pass to the

function here and this is really

powerful after we have this constructor

parameters that will be used to

construct our cylinder object so we can

red param and we can say height and say

height param here and these are going to

be used to construct our object now we

can head over in the main function and

change how we construct our cylinder

object if we want to use tan as the

height we can do that by passing

arguments to our constructor here

let's run this through the debugger

again and see that our information here

now this constructor here is going to be

chosen by the compiler because it is

more fitting for the call that we are

doing here let's run our debugging

session the program is going to be bolt

and we are going to try and maximize

this a little bit and bring up our

terminal output okay we have hit the

breakpoint here we can step into our

constructor and notice the constructor

that the compiler chooses our

constructor that takes parameters is

chosen here and we can do things inside

let's hit next we're going to initialize

the base radius to 10 and we're going to

four okay we can see that to the left

here if we hit next the height is going

to be changed to four and our

constructor is going to be done we're

in the main function again and if we

step over now we're going to print a new

volume which is based on the information

we used to construct our object here

this is really what constructors do they

are used by the compiler to build your

objects and we saw the syntax we can use

to set up constructors for our own

classes okay now you must be saying if

we need constructors to build our

why was the code in the last lecture

in the last lecture we did something

like this we said cylinder cylinder one

cylinder one and this was welding and

compiling fine and let's try and take

out our constructors we can do that

let's comment them out and if you look

you're going to see that the code is

going to compile fine even if we don't

have any constructors in here let's

build with gcc to show you that the code

is going to compile both is good so how

constructing our objects even if we

don't have any constructors in here well

the reason is the compiler is going to

set up its own constructor and what it

is going to set up is a constructor

which is really empty and doesn't have

anything inside it's basically going to

be as if we put in an empty constructor

let's copy this and actually show you

this we can do that and we're going to

make this constructor empty and not do

anything in the body this is the

constructor that your compiler is going

to generate and if we're both now and i

set up a break point here you're going

to see that our empty constructor is

going to be chosen let's debug and show

you that okay you see that we're going

to hit the breakpoint here and if we

step into the compiler is going to

choose this guy and it's not going to do

anything so it's basically going to take

they are and it's going to use the

information to print the volume here we

and get out of our constructor

step over we should print our volume

which is going to be 3.14 because the

initial values we have in our member

variables here so again the message is

if you don't have any constructor in

your class the compiler is going to

generate an empty constructor for you

and the empty constructor is going to

take no parameters and it's not going to

have anything in the body it's going to

be an empty constructor and it is called

a default constructor generated by the

compiler this is really all i had to

share in this lecture i hope you found

it interesting now you should have

enough knowledge to build your own

constructors for your classes we are

going to stop here in this lecture the

next one we're going to learn about

and meet me there in this lecture we're

constructors and this is a syntax you

generate a default constructor for you

all you have to do is do things like

this you're going to say the name of the

constructor which is going to be the

same name as the class you're going to

put in an empty parameter list and then

you're going to say equals default

if you do this the compiler is going to

generate a default empty constructor for

in the last lecture we have seen that we

can set up our own constructors

basically like this what i haven't told

you is that the moment you set up your

own constructor the compiler is going to

not generate the default constructor and

if you want to keep the ability to

construct objects without passing

parameters you're going to have to put

in your own default constructor and you

can use this syntax here to do that

let's head over to visual studio code

and talk about this a little more okay

here we are in our working folder the

constructors we're going to grab our

template files and we're going to put

them in place and we are going to open

this in visual studio code by dragging

and dropping here and we're going to

open our main cpp file let's take out

what we don't need we're going to clean

the main function here and we are going

to bring in the class definition we had

if you remember we had two constructors

and one constructor which didn't take

any parameter and another constructor

which was initializing our member

variables with parameters that we passed

in this parameter list here but in this

lecture let's take out this constructor

that doesn't take any parameter

and show you that when you set up your

own constructor the compiler is not

going to generate a default constructor

for you and we're going to lose the

ability to construct objects without

passing parameters the syntax we

basically see here we're going to say

cylinder and say cylinder one let's use

a lowercase c and if we do this you see

that we have a squiggly line the

compiler is not going to generate an

empty non-parameter taking constructor

because it sees that we have a

constructor here this is how c plus plus

compilers work if they see that you have

any constructor in your class they're

not going to generate a default empty

constructor and if we try to build we're

going to get an arrow that says

we don't have a constructor that can

basically construct an object from the

line here it's going to say no matching

function call for cylinder cylinder you

see here it is trying to call a

constructor that doesn't take any

parameter but we have no such

constructor in our code we could go in

and for example say cylinder and put an

empty parameter list and put an empty

body now this line here is going to work

because we have a default empty

constructor and if we weld you see that

the build is going to be good okay we

are building fine but having to type all

this if what you really want is an empty

is too much type in and in c plus plus

we have a syntax we can use to let the

compiler generate this kind of

constructor for us and the way we do

that is say cylinder and we say the name

of the constructor we say equals and we

say default if we save this the compiler

is going to generate this constructor

for us and the line here is going to

work so let's bring this up and build

again we're going to build with gcc

you're going to see that the build is

good and we can bring up the terminal

and clear and run rooster we're not

going to see anything because we're not

printing the volume of our cylinder here

but we can do that let's call this

cylinder one to be consistent with what

we did in the last few lectures and

we're going to say hddc out and print

the volume of this cylinder we're going

to say volume and call our volume method

and now that we have this we can weld

we're going to use gcc to do that the

build is good we can go down and clear

and run rooster we're going to see that

we see our volume here and this is

really all i wanted to share with you in

this lecture that you can use this

default syntax here to set up an empty

default constructor for your classes and

is that your constructors have to be

public to be able to be called like this

and to show you that let's go up and

actually change this to private and show

you what happens the moment we do this

we're going to get a squiggly line in

the main function here and if we try to

build but before we build let's show you

what visual studio code is saying it's

going to say cylinder cylinder declared

is inaccessible so you see the

constructor which is declared inside of

it accessible from the outside when we

try to call it to build our cylinder

objects so for constructors to be usable

on the outside here and both your

objects they have to be public let's

build and see what gcc says about this

we basically going to have the same

error the constructor is private within

this context so we can't really call it

so if we want our code to build we need

to make our constructors public and this

you need to know let's build again and

see that the cold is now building the

world is good and this is really all i

had to share in this lecture we are

going to stop here in this one in the

next one we're going to see how we can

use setters and getters to modify things

go ahead and finish up here and meet me

in this lecture we're going to learn

about setters and gators and these are

methods in our class that we can use to

read member variables or modify data in

our member variables let's look at a

simple example and by the way i am sorry

for my bad pronunciation of cylinder

here i have said it was cylinder and

after some careful thought i checked

online for the pronunciation on this and

i found that it was cylinder sorry for

this if it was bothering you i apologize

for the bad pronunciation and i am going

to do this right starting from now okay

here we have our cylinder class we have

a few member variables and we have the

base radius we have the height and now

we want to go through some public

functions to do operations on these

member variables because now that they

are private we can't really modify them

or manipulate them from the outside and

we really need to do things with them so

if we want to read things from them we

will use the getter functions

and if you look here this is a simple

function the only special thing about it

is that it leaves inside the class it

has a return value it has a function

name it has a parameter list and then

the body we're just going to return the

member variable of interest because this

is a getter we use that to get stuff

from the class this is the meaning here

here we have another getter function

which is going to return the height and

notice that these functions live in the

public scope of our class this is key

because we want to be able to go through

them to modify and do things with our

member variables but they will be used

from the outside so they must be public

otherwise they want to be accessible

from the outside we also have a pair of

setup functions they are going to be

modifying our member variables so set

base radius is going to take a parameter

that it's going to use to set a base

radius set height is going to do the

same it's going to take a parameter and

it's going to use that to assign a value

to our height member variable here and

because these functions are members of

they have access to our member variables

regardless of whether they are public or

private so this is going to work we're

going to go through them from the

outside and they are going to do the

dairy work for us and do things using

our member variables to which we don't

from the outside this is the meaning

here now that you have an idea about

this we're going to head over to visual

studio code and play with us a little

more okay here we are in our working

folder the current project is setters

and getters we're going to grab our

template files pretty quick and put them

setters and getters it is let's grab the

folder and we're going to open this in

video studio code by dragging and

dropping here this is going to open our

folder we're going to open our main cpp

file and we're going to clean it up a

little bit we are going to grab the

cylinder class from our previous lecture

and use that as a starting point here

and if you look we have a pair of

constructors here we have the volume

function which is going to give us the

volume of our cylinder here and we have

our member variables now what we want to

do is to be able to do things with these

member variables from the outside in the

main function here and we're going to go

through setter and getter methods which

must be public so let's do that so we're

going to set up our getter first so

we're going to say double get base

radius it's going to return double it's

not going to take anything and and in

the body we're just going to return our

radius let's return that okay so we're

going to set up another getter which is

going to give us the height and it's not

going to take anything and it's going to

just return our height member variable

now these are our getters they are going

to be getting things from the class

object we're going to set up other

functions that are going to be our

setters they're not going to return

anything and we're going to say set base

radius and it's going to take a double

parameter in and we're going to use that

to set our base radius so we're going to

say base radius and we're going to say

equals red parameter here and we're

going to do the same for our height so

it's not going to return anything the

function here and we're going to say set

height and we're going to take our

parameter n so i'm going to say double

height param and we're going to use that

stuff to our member variable we're going

to say hi and we're going to say height

param okay so this is our thing here now

we have two functions to get stuff from

our class and we have two functions to

set data to our member variables here

and again remember that we can't have

direct access to these member variables

on the outside of the class and if we

want to do that we're going to be able

to do that through our setter and getter

functions now for these functions

setters and getters to be accessible

from the outside they needed to leave in

the public section of our class you see

this public keyword here is going to

apply to anything after it until we

change this to private software so the

public scope is basically going from the

all the way to our set height function

and once we put this private keyword

here everything after that is going to

be private this is how these things work

so let's try and use this in main we're

going to set up a cylinder object

cylinder one and let's put in for

example two and three why not and now if

we want to have access to the base

radius remember if we tried to access

that directly let's say that if we try

to do something like cylinder one and

say base radius you're going to see that

we're going to have a squiggly line

meaning that there's something wrong

with our call here let's bring up a

and see what visual studio code thinks

about this membership base radius

declared this inaccessible here if we

try to weld we probably going to get a

compiler error that says that base

radius is private in this scope and

that's what we have here declare the

private here so we can't access this

from the main function here but now that

we have our getter functions we can go

through them and have access to

private member variables and notice that

because we are returning by value here

what return is going to be a copy you

really need to keep an eye for whether

what you are manipulating is the

original stuff or a copy so here we're

going to be returning by value and we're

going to return a copy but this is still

useful in some cases so here we can use

allocator let's take out this here and

say get base radius it is a method or a

function so we need to put our function

call here and now if we try to build

let's pass this through gcc and see what

we get you see the build is good we can

run this program let's clear and run

rooster you're going to see that the

base radius is two now now that we have

this sense we can actually modify stuff

about our cylinder here let's put in 10

and 10 just to be able to follow this

easily and we're going to print the

volume let's say volume and we're going

to say volume here we're not going to

use the getter here i'm going to say

volume this is going to print our volume

but we're going to modify our member

variables remember this is an object of

so we're going to say cylinder 1 set

base radius we can do that and we can

change this to 100 for example and we

can change the height that height we can

use this member function because we have

it now and we're going to set this to 10

why not now if we print the volume

you're going to see that the volume has

changed because we are going through our

setter and getters methods so the

cylinder is now going to be using this

data and for the first case here the

cylinder is going to be using the data

we used in our constructor here let's

both and run this application the build

is good we can clear and run rooster now

for the first time we're going to see

that our volume is this number and for

the second time our volume is going to

be multiplied by 10 because we changed

the base radius to 100 and if you put

these numbers in you're going to see

that they make sense we are able to

modify our member variables through our

setter and getter functions and again

for this setter and getter functions to

work they have to be in the public scope

of your class because if you make them

private they're not going to be

accessible from the outside and you're

going to get a compiler error let's try

and do that we are learning so we're not

afraid to break things a little bit so

let's make them private we can do that

and bring this a little bit to the left

and at the moment we do that we should

have a few squiggly lines in our main

function and we do expect this because

they are private now so we have no

business accessing them from the main

function like this they are meant to be

used from the inside of the class if

they are private like this and if you

try to use them from the outside you're

going to get a compiler error let's pass

this through gcc to really see the

compiler error and we're going to get

set height is private from the context

of the main function and if we go up i

think we're going to see the same thing

for a set base radius and that's here

this is really all we set out to do in

this lecture showing you how you can use

setters and getters to manipulate your

member variables from the outside

and i hope you found this useful we are

going to stop here in this lecture in

the next one we're going to show you how

you can split your class across multiple

files but before i let you go let's fix

this so that we don't have a compiler

error here so we're going to remove this

private keyword we have put here and

we're going to build again to make sure

the world is good let's use gcc for that

the world is good and i will see you in

the next lecture go ahead and finish up

here and meet me there in this lecture i

am going to show you how we can split

our class information across multiple

files so far what we have been doing is

really cramping everything in the main

function we had our constant declaration

we had our cylinder class definition and

we had our main function to use these

things all cramped into the main cpp

file now we're going to see how we can

do things better the first thing we can

do is move our constant in another file

because if you think about it users of

your class in the main function don't

care about this constant pi because it

really is an implementation detail

that should leave somewhere else or even

inside the cylinder class but we're

going to put this in a separate file

because that's going to give us room to

put as a constant if we need to do that

so if we split things up like this

when we want to use the pi variable we

will need to include the constants file

because that's going to give us access

to it but we don't have to maintain it

in the main function so this is a little

better but another thing we can do is

remove the cylinder in another separate

file and do something like this so now

you see that our cylinder declaration

and definition has moved in a file

living in another file called

and if we want to use our cylinder class

like we have been using it all along we

will need to include the header that

brings it in and this is how we're going

to do it and we will be able to use it

in the main function if we set things up

like this but we can go even further we

can split our class declaration and

definition in two separate files what

we're going to have in the header is

going to be really a preview of the

and in the cpp file which is going to be

cylinder.cpp we're going to have the

implementation details of our class and

again this is going to make things a

little easier to manage because it's

really not good to have everything

cramped into your main cpp file it

should really have high level details

about how your application works and all

the low level details should be split

into different files this is good design

now that you have an idea about this

let's head over to visual studio code

and show you how you can do this okay

here we are in our working folder the

current project is class across multiple

files we're going to grab our template

files and put them in place and we're

going to open this in visual studio code

so that we can really play with us this

is going to open our folder we can open

the main cpp file we are going to clean

it up a little bit and we are going to

grab our class definition and put that

on top here so this is our cylinder

class we have the constructors we have

the functions the volume function here

and we have our setters and getters

inside down we have our member variables

which happen to be private to this class

here now what we want to do is to

our code better and the first thing we

need to do is to move this constant from

the main file here because it's really

not that useful at this point here users

of your classes won't really care about

what pi is because it is an

implementation detail to the cylinder

class because we are using that to

compute our volume so this constant

really has no business being in the main

file we're going to move this in a

separate file we're going to set up a

new file we're going to come to the left

here click on the plus icon here that

says new file we're going to say

constants and we're going to call this

constants.h because it's going to be a

header file and we can just come from

main cpp file we're going to copy this

we're going to cut this actually and

we're going to put this in our separate

after we do this we're going to come in

our main cpp file and we're going to

include that header file so let's do

that we're going to include constants.h

and the moment we do that you're going

to see now visual studio code knows

where this constant is but we don't have

to deal with that directly here another

benefit of doing things like this is

that we can go in this header file and

declare thousands of other constants and

we can have access to them in the main

function by just using this single line

that includes our file here so this is

good design if we build our application

you're going to see that it is going to

work let's try and set up a cylinder

object we're going to say cylinder 1 and

we're going to put 10 and 10 n as our

parameters and we're going to print the

volume of this little guy so this is

easy to do now we're going to say volume

and we're going to print that out

cylinder one and we're going to call the

volume method and this is going to print

our thumb and again i am going to be

using the terms functions and methods

interchangeably in this course and what

i mean in the context of the class

that's going to be the member functions

of the class so don't be confused by

this right here if we build and run this

application it should be working right

because we have everything we need for

let's see if the world was good the

build was good we can bring up a

terminal and actually run this let's

clear and run rooster this is going to

print our volume so the code is working

right the second thing we want to do is

to move this class all together in

another file because we don't really

here in the main function what we really

want is to use stuff and we don't care

about how those things are set up in the

same logic we used when we used std

strength we didn't really care about how

hdd strength is put together all we

really wanted was to include the class

that brings it in and use it in our code

we're going to be setting up the same

behavior for our cylinder class here and

it is going to be given in its own

separate file so let's set up another

header file we're going to call this

cylinder dot h and we're going to grab

our class definition all together so

we're going to go from the bottom here

and select everything that includes our

class we're going to cut this out we're

going to go in our cylinder header and

we're going to paste this in there and

we're going to come back to our main

file and include our cylinder class so

let's do that we're going to include and

we're going to say cylinder.h

and this is going to make things work

remember the preprocessor is going to

put these things on the preprocessor is

basically going to go in constants it's

going to take whatever is inside and

then it's going to paste that here and

it's going to take everything inside our

cylinder class and it's going to paste

that here so it's basically going to be

like we are declaring these things in

the main function but our code is going

to be better organized now if we try to

build this program it is going to world

exactly like it did because we have all

the information for its world let's

build world has finished successfully so

the world is good and we can run this

program and it's going to do what it was

doing all along we can clear and run

rooster don't worry about visual studio

code here i don't know what the problem

is with that it's just having ah it's

constant here because it's not included

in here so what we can do is say include

and include our constants header and if

we do this the problem here is going to

go away but we're going to have a

problem if we're trying to run this

program now because try to think about

it in the main function we are including

header of cylinder we are also including

this little guy here so if the processor

this and it's going to have this little

guy inside our main function and the

cylinder is also going to include this

because it's including this header so

when the preprocessor is done we're

going to have our constant here declared

twice and if we try to build this

program you can expect bad things to

happen because it's really not good to

have the same thing defined more than

once in your entire program and let's

try and build and show you this

hopefully we're going to get a compiler

and it's going to blow up in our face

it's going to say hero redefinition of

const double pi so what is going on here

we are including this thing twice once

here and at the second time it's coming

in directly from the cylinder class

because we are including that in this

location here and what the preprocessor

is basically going to do it's going to

copy the entire file here and it's going

to paste that in the place of cylinder.h

here and this constants header is

basically going to be included twice so

it's going to be redefined here that's

the problem we have one way we have to

solve this in c plus plus is by using

include chords and the way we do that we

come in our constants header and we say

if something is not defined yet and

let's say cylinder underscore h and

cylinder underscore h and we're going to

come down to the end and say and f this

preprocessor to only do something or

include the code we have within these

things if the condition on top here is

satisfied so for example the code inside

here is going to be put in our c plus

if the cylinder name here is not defined

in the eyes of the preprocessor so it's

going to say if cylinder underscore h is

not defined i am going to define that

and i am going to put this code here but

if it's already defined it's going to

skip all these things and it's not going

to include this okay so this is the

logic here and i noticed this is really

not a cylinder file so we're going to

underscore h let's say that and let's do

the same here and this is going to do

our thing and we're going to go in our

cylinder header and do the same thing

and put in our include guard it is

basically a guard that is going to guard

being included more than once

so let's do that in our cylinder header

so we're going to wrap this inside our

include guards we're going to say if n

def you see visual studio code is really

helping out here and we're going to put

in the name we're going to use for this

this is a cylinder class so i think it

makes sense to call this cylinder

underscore h and we're going to do the

same thing here define cylinder and

we're going to end f at the end of the

file here so we're going to say end f

and again this is the syntax of the

preprocessor i don't want to get too

much into this because we will learn

about this later in the course but we

can now use this to guard against

something being included more than once

and if we're trying to build the program

now hopefully it's going to world let's

use the gcc and now you see that the

world is good even if we are including

the constant header multiple times in

the main file here we can even go down

and do that like a thousand times so

let's do that and you're going to see

that if we try to compile it is going to

boil define because now we have a guard

guarding against including this thing

more than once the preprocessor is

basically going to come in here and say

the constant's name is not defined i'm

and i am going to put the code here in

the source file that includes me

if it happens to be already defined this

condition here is going to fail it's not

going to do any more than in this file

the preprocessor is basically going to

give up on this file here this is what i

want you to know so now we should be

able to split our code into multiple

files and now that i think about it we

don't really need to include the

constants header here because it's going

to be broadened by the cylinder class

but it was a good opportunity to teach

you about the include guards here now

that you notice we're going to remove

this and we're going to build and show

you that this is going to work anyway so

weld is good we can run our program

clear and run rooster this is going to

work the last thing i want to show you

is that we can go even further and split

our class into two separate files

because people who come to the header

file are usually interested in your

class definition they are really not

interested in your implementation

details for example they want to see

that you have a volume function and they

want to know that they can call that

function but they don't really want to

know how you compute your volume and we

can really make events simple for them

and hide the implementation details in a

separate cpp file so let's do that we're

going to set up a new cpp file we're

going to call this cylinder that's cpp

in the cpp file and i am doing this just

to show you that it is possible in

practice you're going to have to decide

for yourself what you want to keep in

the header file and what you want to

keep in the cpp file so the cylinder

default constructor here is going to

stay this way but we can move the other

constructor here in the cpp file and the

way we do that we're going to just grab

this and i am going to change this line

by line so that you can see this

and in the cpp file the first thing we

want to do is to include the cylinder

header because the implementations here

and we're going to put in our

constructor and modify it to be fit for

living in a cpp file so let's come here

and do that the way we tell this that

this is really an implementation of a

function we have in our header here is

to put the class name in front we're

going to say cylinder and put two

columns the moment we do that the

compiler is going to know that this is

an implementation of a function we have

in our header file and this is the

function here and now we can take out

the body here and live this as a

prototype for the function which is our

constructor view we can do this

okay if we do this in world the code is

going to world it's going to construct

our objects let's go back in main cpb

constructor we are using it is we can

weld and make sure that what we just did

didn't break anything we are building

and we can clear things up a little bit

and run rooster this is going to give us

our volume and we have started to split

in our class here some things are going

to leave in the header file some other

things are going to leave in the

implementation file so we have moved our

constructor here let's move the volume

function we can grab it and i move

things line by line i think this is the

and i think we can move this things a

little bit to the left let's do that and

we're going to say that this is a

function implementation for some

function that is declared in the class

here so we're going to say cylinder and

we're going to put two columns this is

going to tell the compiler this is an

implementation of the function we have

in our class and the return type has to

live in front of this scope resolution

operator okay what we have here cylinder

column column is called the scope

resolution operator and is basically

telling the compiler that our function

called volume leaves in the scope of the

cylinder class this is what the syntax

here is saying and this little thing

here is called a scope resolution

okay so we have moved our volume

function we can now take the body out

from the class and keep the prototype

here we can go down and really practice

on the setters and gators so let's do

that so we're going to grab them all

together because now you have the gist

about how this works we can copy them

and move them into the cpp file and

we're going to fix the code lined by

line here so let's make sure they are

aligned properly we have two left to do

let's do that and i really have to show

you this life because some people are

going to have problems regarding how i

did this so i want you to see this live

as i do this i'm not going to edit this

out so we're going to put our scope

resolution operator after our return

type here i'm going to say cylinder

cylinder can't type can i okay we have

this in and we can really copy this and

paste this into place wherever it is

needed so i'm going to paste that here i

am going to paste that here and i am

going to paste that here now we have

successfully moved all the functions in

cylinder.cpp and we can go back in our

header and remove the bodies because we

don't need them here if we keep them

here we're going to have two definitions

for this functions and we're going to

have compiler errors let's take this out

we're going to take the body out we're

going to take the body out and we're

going to take the body out let's do that

and now if we build our program it

should work we're going to work with gcc

see the world is good and if we try to

run the program it should give us what

it was given before this is the volume

one thing i want you to see is that you

don't want to keep two definitions for

your functions so for example we can

grab the body here and bring this back

in the header file i want you to see

what's going to happen if you do that i

am going to paste that in here and i am

going to move things a little bit to the

right to align things properly here so

if we do this the compiler is going to

see that we are calling that constructor

and the compiler is going to have no

problem with us but once we hit the

linker stage the linker is going to find

that we have two definitions for the

constructor here we have one in the

implementation file and this is going to

raise a compiler error saying we have

two definitions for the constructor here

and the linker want to know which one to

use so it's going to give you an error

let's build and really show you this

because this can be hard to debug if you

don't know what is happening okay you

see we have world finished with errors

and the problem is cylinder cylinder

double double is redefined we don't want

to have two definitions for the sum

function so once you move things from

header to implementation file be sure

you don't have any more definitions left

in the header or you're going to have

really hard to debug problems

and now i think we have our program

organized fairly well for what we know

so far about c plus plus we have our

constants living in another header file

and we have learnt about include cards

what we can use to guard against our

stuff being included more than once by

the preprocessor we have our cylinder

class living in its own file and again

we have an include guard here and you

can see that this class now is really

easy to look at we can look at the

information about the member functions

we have for example we have a default

constructor we have a constructor that

takes two parameters but we don't see

the details about how these things do

their jobs for example we don't see the

details about how the volume is computed

those details are hidden in the cpp file

and if you want to see them you need to

go to this implementation file here this

is a good design and i encourage to

split your c plus plus programs in

multiple files like this this is going

to make your life easier in this lecture

we're going to see how we can manage our

class objects through pointers and in

most cases we need to manage our class

object through pointers if we are using

some form of dynamic memory allocation

here is a simple example we have our

cylinder class included and down here

you see that we can create cylinder

objects on the stack if we use the

syntax like we do here the objects are

going to be created on the stack and we

have seen that we can access the

behaviors or data inside our class

object using the data notation like we

do here for example here we are calling

our volume function but sometimes we

want to manage our objects through

pointers for example if you look at the

syntax we have here we are saying

cylinder and using the asterisk here

this is going to say that this is going

to be a pointer to a cylinder type

and i'm going to give it a name c2 and

we can allocate our object on the heap

using the new operator this is going to

dynamically allocate space from the heap

and that memory space is going to be

used to store our cylinder object now

the interesting thing is going to happen

when you try to access behaviors from

your cylinder object here for example if

we look at this line here we are trying

to print the volume of this cylinder and

you notice that we have to go through

ugly dereferencing here we have to

dereference the object and then call our

method through the dot operator here but

what i want you to see is that we can

avoid this ugly the reference that we

are doing here and use the pointer

access notation this dash greater than

symbol you see here is going to allow us

to access stuff directly using the

pointer to an object that is dynamically

allocated on the hip okay after we are

done using our cylinder object remember

it is memory that was dynamically

allocated from the hip we have to

release the memory so that it can be

used by the operating system and we

release the memory using the delete

operator as we do here okay the idea i

wanted to introduce here is that we can

use players to manage our cylinder

objects and this is one way we can do

this and once we are using a pointer as

a handle to our cylinder object we can

use the pointer access operator here to

access stuff from our class objects

easily and another thing you should know

is that we can actually create a

cylinder object and store in the address

of objects that we have on the stack and

we're going to see this in a minute when

we hit visual studio code now that you

have an idea about this let's head over

to visual studio code and play with this

a little more okay here we are in our

working folder the current project is

managing class objects through pointers

we can see the entire name here and now

we're not going to grab our template

project because we want to start from

the project we had in this lecture on a

class across multiple files so we're

going to go in that project and grab

except for the executable because we

and we're going to go in our current

project and paste in the code and this

is going to give us a good starting

point so we can grab this and open

this project in visual studio code it's

going to open the folder and we're going

to have everything we want to start

doing what we want to do in this lecture

here so now we should have access to our

cylinder class and if you look here we

have an object of cylinder type already

created by this line on liner number six

here and we have seen that we can use

the syntax like cylinder volume here

using the dot call operator to access

stuff from our class object and this is

going to work but we want to see that we

can use pointers to manage our object

here and the first thing i want you to

see is that we can manage a stack object

through pointers and to really show this

another variable it's going to be a

cylinder pointer and it's going to be p

cylinder one it's going to be a pointer

to cylinder one here that's what i mean

and we can give it an address of

cylinder one as a value so we can do

that for example and put in the address

of operator and this is going to work

now we can go through our pointer here

and do stuff with this cylinder object

but the syntax is going to be pretty

ugly so for example let's try and print

we're going to say htdcl and say volume

can save that and we're going to have to

go through the dereference operator so

if we do something like p cylinder one

and try to use the dot operator

you're going to see that we have the

volume function but if we try to call it

let's do that let's make sure we are

using the dot operator here if we try to

compile this program it's not going to

we are trying to call stuff from a

pointer and remember a pointer is just

going to store an address it doesn't

really have information about the type

that it is pointing to if we try to

compile this program we're going to get

a compiler error so let's use gcc to do

and we're going to get request for

member volume in pc lender 1. remember p

cylinder 1 is just a pointer it's not an

object so we can't really call the

if we want to use the dot call operator

here we have to the reference and

object that the pointer is pointing to

and we do that using the star operator

you already know how to dereference a

pointer so we can dereference our

pointer and then call the volume

function on what the pointer is pointing

to and this is going to work it's going

to print out volume let's build now now

that we are dereferencing correctly and

you see that this is going to work and

if we try to print this let's bring up a

terminal so that we can run this program

let's run rooster you're going to see

that we have our volume here so to

really get to what is pointed to

you need to use the reference operator

and then call whatever method you want

to call on your object but we can do

things even easier there is a syntax we

can use to use the pointer directly here

because going through all this

dereferencing ugliness is really not

cool so we're going to grab this and

show you that we can use the dash

greater than operator that's how i

and if we use that we don't need to the

all we need to do is use the dash

greater than symbol here and it's going

directly tell the compiler don't code

stuff on the pointer directly do the

reference the pointer internally and

then call the volume function on

whatever you get after referencing so

this is basically going to push the the

referencing ugliness here behind the

curtains of the compiler and we can use

a nice syntax like this and i think this

is much better than what we were doing

here so if we try to bolt now we're

going to build and print our volume

you're going to see the bolt is good you

can clear and run rooster you see we see

our volume here so this is what i want

you to see it is possible to manage your

cylinder objects through pointers and

this is one way we can do this by

managing a stack object through pointers

and this is what we are doing here if

you want to call stuff on your class

object you can either do the ugly stuff

we do here or you can use the nice

pointer access operator and it is going

to be cool okay now that we have seen

this let's see another use case in which

we're going to be creating a cylinder

object on the heap through the new

operator okay we can go down and save

that we're going to say cylinder pointer

c lender 2. we can call it like this and

then we're going to say new cylinder and

you're going to see that we can call a

we have two types of constructors we can

call we're going to call our constructor

that takes two parameters and we can

100 why not oh let's put the two after

here we can put in whatever we want this

is going to create a new cylinder object

the space for the cylinder object is

going to be allocated on the hip so this

is a hip object and because we are using

the other thing you should have in mind

is that you will need to release this

memory and let's go and do that directly

this is a good practice because you will

forget to release your memory if you

don't really keep this in mind so we are

going to delete p cylinder 2 because

that's what we used to allocate our hip

memory here okay now that we have taken

care of memory management we can go in

and use our p cylinder to object

and for example we can print its volume

by using the stdc out statement here so

let's go down and save that

let's align this properly and we're

cylinder 2 to really make this super

clear and then we're going to say p

and call the volume function here this

is going to work let's draw in world the

world is good we can clear and run

rooster this is going to give us our

volume and if we try and use this

information to create a cylinder we're

going to see that the volume is what we

see here we can even try and print its

let's do that we're going to say sdd cl

we're going to say p cylinder 2 and

we're going to say base radius we can

hit the dot operator here you're going

to see we're going to have a few options

in a visual studio code here if we

double click on get base radius here

you're going to see that visual studio

code is going to use the pointer access

operator here and this is really cool so

we can hit std and yeah we can close the

left pane here because we need some more

breathing space and if we try to

build and run this program and we have a

compiler error here and the reason is

get base radius is a function

if we go back in our cylinder class we

see that we have a function called get

base radius so if we want to call this

in the main function we need to call

that as a function so we need to put a

pair of parentheses here and if we build

we should build without a problem let's

you see the build is good and if we run

the program we're going to see exactly

what we expect let's run a rooster we're

going to see what we expect here and the

message here was really that you can

class object through pointers one case

is when you have a pointer that is

pointing to a stack object and we saw

that we could do that here we can also

use pointer notation to allocate

objects on the heap and point to them

with our pointer here and whenever we

are using a pointer we have the option

to use the pointer call operator here to

do things easily i am going to be

calling this the pointer call operator

to mean this from here on if we happen

to need this and you should know what i

mean by that this is really all i set

out to share in this lecture i hope you

found it interesting we are going to

stop here in this lecture the next one

we're going to learn about these

go ahead and finish up here and meet me

there in this lecture we're going to

learn about these structures these

structures are spatial functions or

methods in a class that are called by

the compiler to destroy your object and

these are going to be especially useful

if you are for example allocating memory

let's look at the simple example here we

have a class called dog it has two

sections the public section and the

private section in the public section we

have two constructors a default

constructor that doesn't take any

parameter and a constructor that takes

the parameters are going to be used to

initialize our member variables and they

are passed by a value here for

simplicity and they are going to be used

to initialize these member variables

doug name dog breed and dog age

the special thing about this class is

that it has a destructor and you declare

syntax here he puts a tilde character in

front you say the name of the class and

then you put an empty parameter list it

is also possible to declare a destructor

and put in its entire body in the header

and this is the syntax to do this

inside the body you're going to do

whatever it is you need to destroy your

object for example if the class here is

constructor the destructor is the best

place to release that and this is an

example of how you can do that here is a

more direct example of how we allocate

for dynamic memory in the constructor

and release that memory in the

destructor we have our three variables

but we have chosen to allocate

our dog edge variable on the heap using

dynamic memory allocation and after we

dynamically allocate a piece of memory

to store our age variable we're going to

set that to 0 because we are in a

constructor if we are using the three

parameter constructor here we might use

the past parameter to initialize our age

variable but the important thing here is

dynamically educated memory on the hip

here and when our object dies we need to

remember to release that memory and the

destructor is the best place to release

that memory as you see here we say

delete dark age when our object dies and

the compiler is going to call this

function when it's about to kill the

so you might ask when are destructors

really called we are going to start by

looking at obvious cases here for

example when a local stack object goes

the destructor is going to be called

because that object is going to be wiped

out from memory so this is an obvious

in which the compiler will need to call

a destructor also when a hip object is

released from memory using delete the

destructor is also going to be called

but there are some indirect ways in

which the structures are also called for

example when an object is passed by a

this is going to call the destructor to

kill the object when the object goes out

of scope in the function because when an

object is passed by value we're going to

have a copy in the local scope of the

function and when the function exits

that local copy is going to be killed

and we're going to see an example of

that another case where you might have

the the structure called is when a local

object is returned from a function

another copy is going to be created to

be used outside the function and the

copy inside the function is going to be

killed but this is not guaranteed as

some compiler may optimize your return

value and use some kind of reference so

you're not guaranteed to see this

behavior but it is possible to see it

now that you have an idea about

destructors it's time we headed over to

visual studio code and play with us a

little more okay here we are in our

working folder the current project is

the structures we're going to grab our

template files pretty quick and we're

going to put them in place and after

that we're going to open our folder in

visual studio code by dragging and

dropping here this is going to open our

folder and we will see our main cpp file

here we can open it and i clean up and

remove what we don't need we have an

unneeded breakpoint here we can remove

that and we're going to clean up the

main function the first thing we want to

do is to put in our dog class i am going

to just put this in here because i don't

want you to watch me type all this

that's just going to waste your time we

have two sections in the dog class we

have a public section which is going to

now contain our constructors and we have

a private section which is going to

contain three member variables we have

two strengths one for the name and the

other for the breed of our dog and we

have another one which is an end pointer

which is going to store the edge of the

dog and you see that this is initialized

to no pointer one thing you should

notice is that for our parameter taken

constructor we are passing the string

information here using string views to

avoid copies with the std string view

type you already know this because we

learned about this but for this to work

we will need to include a string view so

let's do that and now we have our class

and we can use it however we want

so but before we do we need to put in

the implementations for these functions

one way we can do that is do that

directly in the function here but i want

you to see that you can also do that

directly outside the class here i don't

think i have shown you this but it is

possible to do that so we're going to

grab the prototype for our constructor

and say the scope resolution operator

and we're going to just paste in what we

have copied which is the prototype here

and we're going to go inside put in our

body and in the body we're going to

initialize these three guys

so the name is going to be initialized

to nem param and the bridge is going to

be initialized to breed the param we can

do that and the age is going to be

dynamically allocated from the hip you

see that it is a pointer so we're going

to say ph equals new and because we're

going to allocate dynamic space to store

an end and we're going to put data in

using our good old dereference operator

equals whatever ph parameter they passed

and i think we should say edge here

because it's not a pointer so we're

going to say age i think this is going

to do better age param this is probably

going to be better and we're going to

say age param okay so now we have our

constructor n and it's going to allocate

memory from the heap and we're going to

put data in that new memory location

that has just been allocated to our

class here so this is our class and we

can go in the main function and really

use it however we want for example we

can set up a dog object so we're going

to say my dog and we're going to give it

a name the name is going to be fluffy

and we're going to put the breed in and

it's going to just be a shepherd and

we're going to put in the age which is

going to be for example a 2. let's say

this is valid c plus plus code it's

going to be setting up an object of our

class here and we can world to see that

this program is going to world without a

problem so both is good but if we run

the program we're not going to see

anything but we don't really need to see

our constructor here called because we

already know about constructors what we

want to learn about are these structures

and these are spatial methods that are

called by the compiler when your object

dies let's set up a destructor and see

it called when our dog objects die the

syntax to do that is to use the tilde

character here you're going to say the

name of the class you're going to put an

empty parameter list and if you want you

can put a body and do whatever you want

to do in the body of your destructor

here but again we're going to move the

entire definition of the destructor to

the outside so let's go down and save

that we're going to say the scope

resolution operator we're going to say

dog and we're going to put in our body

and the first thing we want to do in our

destructor is to release this memory

that was dynamically allocated for us if

we don't release it when this dark

object dies we're going to link memory

and that's really bad so let's do that

directly in the destructor we can say

delete and say ph this is going to

release the memory that was allocated in

the constructor here and we have access

to this ph variable because the

destructor is part of our class

any member function of your class is

going to have access to any member

variable even if it happens to be

okay so we forgot our tilde character

let's put that in here and this is going

to be valid c plus plus code but to

really see things happening here let's

put in an sddc out statement we're going

to say doug destructor called 4 and

we're going to say the name of the dog

let's say name and we're going to say

the same thing in the constructor we're

going to say hddcl and say dog

constructor cold for and we're going to

say the dog name going to use our member

variable and now we have our thing in

place we have the destructor declared in

the class definition and this is the

syntax again this is what we really want

to learn about in this lecture we have

the tilde character we have the class

name and we put an empty parameter list

let me tell you that it is not possible

to pass parameters to your destructor if

you do that you're going to get a

compiler error the structures will

always have no parameters in c plus plus

here we have the definition of our

destructor and it is going to release

whatever memory we have dynamically

allocated from the constructor here if

we're going to see our constructor

called as a result of this line here

because we are constructing a dog object

and we're going to see the destructor

called when the main function is about

let's put an stdc out state to mention

the main function here and say done just

to prove that we have hit the end of our

main function here i think this is

useful and we're going to build so let's

do that we're going to build with gcc

you're going to see that the world is

good so we can clear and run or program

let's hit enter here and clear and run

rooster you're going to see that the

constructor was called we are going to

say done when the main function is about

to end but before the main function ends

we're going to destroy any stack data

that we have in the main function and

our dog object is on the stats so it's

going to be destroyed as part of that

process and the destructor for dog is

going to be called and we're going to

release our memory and we're going to

say that dog destructor was called for

we have assigned to our dog here so this

is how destructors are called when your

and we didn't put in the correct name

we said fluffy let's say fluffy because

that's what i wanted and now you see

that our destructor is really being

called and releasing memory however we

want but we can also go a little further

and show you another example of a case

where the structures are called and

we're going to look at a function that

sets up a local object of a dog we're

going to see the dog constructed and

we're going to see it destroyed when the

function is about to end let's do that

we're going to say void some funk and

it's going to be just some function to

play with us we're going to

move our dog declaration in some funk

and this is really it we're going to

and when we call it we're going to

construct the object here when the

function is about to end the compiler is

going to call the destructor because

it's going to destroy this object here

and we're going to see the destructor

called by that point the some funk

function is going to be popped off the

top of the stack we're going to hit the

main function here and we're going to

say done and the program is going to end

let's call some funky name here so we're

going to say some funk and we're going

to world to really see this happening so

we have worked successfully we can clear

clear properly and run rooster we're

going to see constructor called for

fluffy the structure called for fluffy

and you see done we have hit the main

function and really finished executing

our program here we can even see this

through the debugger we're going to set

up three break points one in the main

function here before we call the some

funk function we're going to set up

another one in our destructor before we

print the message here and we're going

to put another one in the constructor

when we are about to print this message

here on line 20. after we set up these

break points we kind of kill the

terminal here and minimize a little bit

let's kill these things here so that we

have a clean ah we have a lot of windows

here okay we have our editor here

and now if we go to the tab here that

says start or run we're going to be able

to click the green button here to start

our debugging session we are going to

have a terminal here so let's bring that

to the side so that we can see things

printed out nicely let's do like this

and now we have hit the break point in

the main function we can step into

the sum func function and we're going to

do that using the step into button here

let's click that we're going to jump

now we have the option to step into but

this is going to jump us into the logic

of transforming the string literal here

into a string view because if you see

the constructor is going to take string

view parameters we can actually see this

and hit the step into button you see

that we are in the string view class and

we don't really want this so let's step

out and we're going to step over this

so that we can hit the next breakpoint

and you see the next breakpoint is in

our constructor and this proves that the

constructor here to build our object

if we step over this we're going to

print the message from the constructor

and if we keep going we're going to get

our constructor and you see where this

is going to go this is going to go in

the destructor because before we leave

the some func function our dot objects

is going to be destroyed so we're going

to release our memory and we're going to

branch the message from our constructor

and if we hit next and a step out of

this i think we can do that because this

is logic we don't want we're going to

try and step over this and now if we hit

next we're going to come back in some

funk and some funk is already going to

be finished and if we hit next we're

going to come back in main and we're

going to print done and the program is

basically going to be done hopefully you

the compiler is going to call our

destructor after it leaves some funk

here because it's going to be destroying

the local object that we have inside

some funk here so this is one case where

the destructor is going to be called by

the compiler and it is if you have a

local object that needs to be destroyed

when function scope finishes another

case where the destructor may be called

parameter by value so let's change some

function here and make it take something

by value so we're going to pass a dog

inside and we're going to say dog param

this is going to do okay now that we

have changed some func here we can

really do all kinds of crazy things with

it for example we can set up our dog

object inside our main function here so

let's do that we can say dog and dog the

variable name is going to be dog we can

a name which is going to be fluffy it's

going to have a breed of shepherd and we

can give it the age of 2 like we have

been doing all along we can call our

function with the dog object here but be

careful about what is going to happen

here when we do something like this

we're going to be passing by value and

the compiler is going to see that it

now we haven't really told our class

here how to copy dog objects and we do

that through constructors we call copy

constructors we haven't really learned

about yet but what the compiler is going

to do by default is copy these things

member by member so it's going to set up

a doug copy object which is going to be

initialized with empty strings and a

null pointer here and then it's going to

that we have here it's going to take the

name and copy that in the name member

variable of our dark copy it's going to

take the breed and copy that n in the

second member variable here and it's

going to take the age from our dog and

copy that in the problem is going to

come to this pointer here it's going to

copy the address and it's not going to

copy what it's pointed to and this is

going to be a recipe for a disaster i

don't really want to go through this

right now but if we try to run this

program it's not going to work like we

expect for example if we pass fluffy

things that we don't expect so let's try

to build we're going to build with gcc

and the bolt is good so what we expect

is to have the constructor of fluffy

here called and we're going to copy the

dot object for use in some funk here and

to set up this copy it's not this

constructor here that is going to be

so it's not our constructor here which

is going to be called so we're not going

this called for the copy that we set up

inside some funk another thing is

because now these two dog objects are

pointing to the same thing because what

we just copied is the address as we see

in our member variable here the two dog

objects are going to be pointing to the

same thing in memory and when we hit the

destructor we're going to call delete

twice and this is going to be a recipe

for disaster our application could

really crash you already know that

deleting a pointer twice is really bad

we shouldn't do this and we are doing

this here because we are copying i

realize this is a slightly confusing

but what i want you to know is that if

you pass a class object by value like

the copy you have inside is going to

cause for the destructor to be called

when the function exits because the copy

is going to be scoped inside the

function here so let's take out this

example because it really is confusing

but i hope you know that and i am going

to show you that another case where you

might see the destructor called is when

you call the destructor explicitly using

the delete operator on your object so we

can set up some func again let's do that

some funk and we're going to repurpose

it and inside we're going to set up a

dag object so let's grab this and reuse

that in our function here and we're

going to say dog pointer so let's say

dog pointer we're going to say p dog p

underscore dog it's going to be equals

to new dog and we're going to pass in

what we need to initialize our dog

object with this is going to create a

dark object on the hip and it is going

to be pointed to by p dog here

now i want you to see that if we don't

explicitly release the memory that we

allocate through the new operator we're

going to leak memory so we created an

object on the hip here but we're not

deleting that in some funk when some

funk exits we're going to lose this

pointer this variable because it is on

the stack itself and we won't have any

way to release this memory let's call

some funk here and really show you this

so we're going to call some funk and

we're going to build let's use gcc for

that the build is good we can bring this

up a little bit and clear and run

rooster we're going to see that the

constructor for fluffy was called

because of this new operator but we

didn't see the destructor called and

so for the destructor to be called we

need to explicitly release the memory in

this function here and we do that by

using the delete keyword and saying the

pointer that is pointing to the memory

that we want to release if we do this

this is going to cause for the the

structure of doubt to be called and if

we run we're going to see our destructor

called let's do that we're going to use

gcc the bolt is good you can clear and

run rooster now you see that the

constructor is called full fluffy and we

have the destructor cold this is really

all i wanted to share with you in this

lecture i apologize if you found it

confusing but if you have any problem i

am always available please do ask and i

will do the best i can to help you out

so the destructor is a special method

which is going to be called when your

object dies it is going to be called

when an object is passed by a value to a

function we have seen an example that

it's going to be called when a local

object is returned from a function by

value but this is going to be compiler

dependent because some compilers are

going to optimize this out and make it

look like when you returned by reference

so i don't want to go into this because

this is subject to compiler optimization

but other cases where you're going to

have your destructor called is when a

local stack object goes out of scope and

through the delete key world this is

really all i had to share in this

lecture i hope you found it interesting

we are going to stop here in this one

and the next one we're going to see the

order in which constructors and these

structures are called and you really

and this lecture i wanted to raise your

awareness on the order in which

constructors and the structures are

called suppose we have our class which

is dug here and we have the constructor

which is doing its thing in the body

here and we have the destructor which is

releasing our memory and printing

something out so suppose we have created

of this class here and they have

different names and they have the same

breed and different edges as you see

and if we run this code in main

what do you think will see printed from

the constructors and the destructors if

you asked me and i was learning about c

plus plus i would say that the

constructors are going to be called in

order dog one dog two dog three dog four

they are going to be constructed in this

order and the destructors would be

called in the same order but this is not

true the destructors are going to be

called in the reverse order as you see

so we're going to call this constructor

for doug d1 delegate2w3 doge4 which is

exactly what i expected but you're going

to see that the destructors are going to

be called in reverse order so the object

is going to be destroyed first as you

see here and the object that was

constructed first is going to be

last and the compiler follows this order

to make it easy for it to do things we

can't really get into those details but

for now we're going to head over to

visual studio code and play with us a

little more okay here we are in our

working folder the current project is

order of constructor and destructor

calls here we're going to grab our

template project pretty quick

and we're going to put them in place the

files i mean and we're going to open

this in visual studio code like we have

been doing all along this is going to

open up our folder we can close the left

sidebar here and let's clean up our main

function we are going to bring in the

class for dog from the last lecture this

no change and we're going to include the

string review library for this to work

so we're going to include string view

here and once we do this we're going to

head over in the main function and set

objects of the dog class here but before

we go there notice that we have a few

htdc out statements in our constructor

and destructor and we want to see the

order in which they are called so we're

going to set up four objects of our dog

we're going to say dog dog one and we're

going to say the name to be won and it's

going to be a shepherd and it's going to

be for example 2 years old why not we

should say dog here and we are going to

copy these four times here and we're

the other is going to be dog 3 and this

and i'm going to say the same thing here

the names are what is really important

because we're going to see them printed

out here but if you want you can change

the ages let's make this a three let's

make this a five let's make this a one

why not for dougie for and now we're

going to run our program if we run it

we're going to see the constructors

called in the order doggy one doggie 2

w3 dog e4 and the destructors are going

to be called in the reverse order

all the way to doggy one let's boil and

show you that this is actually the case

so the build is good we can bring up a

terminal and really run this let's clear

and run rooster you're going to see that

dog constructor called for a doki one

all the way to dog e4 and now we have

the dagger destructor called from doge4

all the way to doge one and the compiler

is going to enforce this order for

calling constructors and destructors

because it makes it easy for it to

manage the memory of objects for example

if duck one has been around for a long

time and it has because it's going to be

after dog four here there might be other

objects that depend on dog one so that's

why the object that was created the last

is deleted first because chances for

other objects to depend on that last

object are really slim and you can

delete it without any problem but the

object that was created first might have

other dependencies and you're going to

be deleting dependent object first

before you delete that object i think

this is the logic the compiler follows

to really enforce this order here and

you need to be aware of that and make

sure that at any time in your c-plus

plus application this is working to your

advantage this is really all i had to

share in this lecture i hope you found

it interesting we are going to stop here

in this one and the next one we're going

to learn about the this pointer go ahead

and finish up here and meet me there

in this lecture we're going to learn

about the this pointer and this is a

special pointer that is maintained by c

plus plus to really help you manipulate

the current object and it is the current

object for which a given method is being

executed here is a simple example with

our dog class and we're going to show

some usefulness for the this pointer the

first thing we're going to look at is

the syntax for example here we might

need to print the address in memory

where the object was created and do that

from the inside of the function and to

do that we use the this pointer for

example we can put out a message and we

can do that through a statement like we

have here we are printing dog dog name

constructed at a given memory address

and we use the this keyword to get the

address of the character object for

which a specific method or function is

being called in this case it was the

constructor of the dot object here we

can also do the same thing for the other

constructor and you see we are using the

this pointer this is one of the uses you

have for the this pointer again the this

pointer is a special pointer that is

maintained by the c plus plus system and

it is going to be pointing to the

current object that is being manipulated

by the z plus plus run time and it's

going to be manipulated through a

special function of the class object

that is being called this is the meaning

here here is another use case for the

this pointer it may be used to resolve

conflicts when you have a parameter and

a member variable that are named the

same way for example here we are calling

the set name function it has a parameter

with a name doug name and it has a

member variable called dog name so if

you do a statement like we have on top

here the compiler is going to be

confused they're going to say dog name

equals dog name and it won't really know

which dog name you are referring to we

can resolve this conflict by saying

this and say pointer access notation

and say dog name and this thing here is

going to be the member variable and

we're going to be assigning to the

member variable from the parameter this

is the meaning here and we can use the

desperator to resolve such conflicts

another use we have for use pointer is

if we want to set up chained calls for

example using pointers and we might need

to do something like this so we have a

dog pointer set up on top here and we

can do something with our new object for

example we can call a function called

printful on a dog object after we print

the information we're going to set some

information on the doc and you see we

are setting all of the information

through one statement the way we achieve

this our setters are going to be

returning a pointer to the current

object and we're going to be grabbing

on it directly because it's a pointer

and we are going to be using the pointer

access notation so we're going to call

set name set name is going to return a

pointer we're going to use that pointer

to say to the breed and set the breed is

going to return a pointer we're going to

use that pointer to set the age and

after this entire line all the

information is going to change about our

dog and we can see that here and after

we do whatever we want with our dog

object we're going to release it from

memory so this is another thing you can

achieve using the this pointer and this

is how you can set up these setters it

is nothing complicated we have set name

it's going to return the dot pointer and

we're going to return this okay and this

is going to be a pointer or the memory

address of the current object of the dog

class we have the same setup for seti

dog breed we return the dog pointer and

we return this the same setup for set

doug age we return a dog pointer and we

this we can do the same thing using

references but our setup is going to be

somewhat a little bit different

we have our dog object here and we're

going to do our change call here so

we're going to say set name through the

because we have a dot pointer here but

after that we're going to return a

reference from the functions here so set

name is going to return a reference

we're going to go through that reference

set dog breed is going to return a

reference and we are going to go through

that reference to set the dog age and if

we print the information now we're going

to see that we have new information in

our dog object and after we are done

with our dog object we have to remember

to release it from memory because it was

allocated dynamically from the heap here

is how you can set this up it really is

nothing complicated we just have our

setters and we are going to return a

reference but before we return through

the desperator we will need to

dereference the displayer and get to the

actual thing that is being pointed to

that's why we have this star operator

here and for the other setters we're

going to do the same thing we're going

to return a reference we're going to

return a dereferenced version of this

we're going to return a dog reference

for set dog age and we're going to

return a dereferenced this pointer

because this is the reference we are

returning here so this is what the this

pointer is about now we're going to head

over to visual studio code and play with

us a little more okay here we are in our

working folder the current project is

the displayer we're going to grab our

template files and we're going to put

them in place and then we're going to

open this in visual studio code by

dragging and dropping here this is going

to open our folder we're going to open

the main cpp file and we're going to

so that we have some more space to work

with i am going to put in a version of

it is pretty limited right now it just

has a destructor and a constructor and a

constructor and we have our member

variables and we're going to

tune this a little bit so that we can

work with us however we want the first

thing we want to do is to print the

addresses of dug objects that we

construct and destruct here and we're

going to do that in our constructor so

let's go to our hd dc out statement here

and we're going to say add to mean the

memory address where the object was

constructed and we're going to say this

so when we do this this is going to be

the address in memory of the current

object that is being constructed

by our constructor here and we're going

to say the same thing in our destructor

we're going to say at and we're going to

say the memory address where the current

object is being destroyed from so after

if we go in the main function and for

example set up a doug object we're going

to say dark we're going to say dog one

and we're going to give it the

information we're going to give it the

name which is going to be fluffy we're

going to give it the breed which is

going to be a shepherd and we're going

to give it the age of two like we have

been doing all along when we do

something like this this is going to

call the constructor because we are

trying to set up an object and before

the main function ends we're going to

call the destructor and we're going to

see things happening here let's say done

so that we know that the code is

actually running i'm going to say sddc

out done here okay we have the setup

we can uh build and run the application

we're going to use gcc to build and the

build is good we can bring up a terminal

to try and run the application and now

if we run rooster we're going to see

that dog constructor called for a fluffy

at this memory location and the current

object is this object here which is

being constructed and we're going to

have access to its memory through the

this pointer hopefully you can see how

powerful this is if we didn't have the

this pointer the only way to get the

this object would be to grab the address

from the main function or from wherever

we are setting up our object here but we

have access to this address from the

inside of the functions for the class

and this is really cool so we can

manipulate these addresses if we need to

and we're going to show you another use

for this so suppose we need to set up

setters for our class here so we need a

setter to set the name the breed and to

set the age here so let's set up our

setters we're going to say setters and

name or let's be explicit set dog name

that's going to be better and we're

going to pass a string view we're going

to say stds friend of you and we're

going to say name program and we're

going to put the bodies in our class

here but i would encourage you to be

consistent if you are doing this in real

code we are learning here and we are

taking some shortcuts so that we can do

things simply but what we want to see

now is what happens if we have a

parameter named the same as a member

this name to the member variable called

the name so if you have a case like this

you're really going to be in trouble

because if you say name equals name

we should get a compiler error or a

squiggly line because the compiler is

which name are you using here is it the

memorial is it the parameter it's not

going to know and let's try to build and

see what we get we're going to use the

and surprisingly gcc is taking this

and it's probably knowing that we have a

member variable named name and it's

going to assign the parameter to that

member variable so behind the scenes gcc

is going to change this to this it's

going to use this name equals name

this is the syntax we want which is

really not confusing but what we have on

top here is going to be confusing and

some compilers are not even going to

take this let's leave this in and

actually build it in with us i want to

see that this actually works so we're

going to weld successfully and if we go

dog one set dog name let's say pumbaa

let's see what happens if we do

something like this we're going to try

and build again and gcc is going to take

this and this is really cool so let's

put in a function which is going to

print information about our dog we can

do that down here and it's going to

return nothing it's going to be called

print info and it's going to basically

print the name of the breed and the age

so it's going to say sddc out we're

going to say the address where the dot

i think that's more meaningful we're

going to say this and then we're going

put a parenthesis and say the name i

think we can put a an angle bracket here

and say name and we're going to say the

dog name we can go down and say the age

or the breed and say the age and we're

going to dereference the age member

variable because it's a pointer we're

going to say the reference ph here and i

think this is going to be it now we can

put a new line character std e ndm and

if we go down now and say printable

before we set the name we're going to

printful we're going to print the

information about this dog and after we

set the dog name we're going to go down

and also say dog one principle you can

play with these things and i really

encourage you to do so so we're going to

build this we're going to use gcc so the

world is good we can clear and run

rooster this is going to say the

constructor was called for fluffy at the

we're going to say the dog we're going

to print the information and we're going

to say it's a dog object at this address

the name is fluffy and we're going to

print the dog for the second time you're

going to see that the name is still

fluffy and we have a problem here why is

why is our object not being modified

let's go up and see our set dog name

function here so we're going to

remove this and we're going to use the

this pointer and we're going to

weld again and let's clear now and run

rooster and now you see that the changes

are actually making sense so what is

happening with the assignment here the

compiler is assigning the value of the

variable to the variable itself and this

is really doing nothing and it is not

what you expect i was fooled a little

bit by the compiler because this was

compiling but it's not going to do what

you want when you call set doug name you

probably want to take this name and

assign that to the member variable name

of this class but this is not what it's

going to do let's build again and really

so it is a really good advice to

practice and really try things out

yourself we're going to run a rooster

you're going to see that after we set

the dog name here to pumbaa and we try

to print the information the information

is not going to be end the name is not

going to be pumbaa for the second call

here and what this is really doing is

doing nothing here this does nothing and

you really need to know this if you want

your remember variable you will have to

go through the this pointer and this is

take the name member variable of

the current object and assign the value

in name the name parameter to that and

that's going to set your name to

whatever new name you passed when you

called the set dog name function here so

hopefully you really understand this now

if we both are going to see that the

pumbaa name has been applied let's boil

again so we're going to clear and run

rooster and we're going to see now that

the name is pumbaa and there is some

constructors we don't have a space

before at here and it is really annoying

to look at here so let's build again and

fix this we are going to use gcc the

world is good we can clear and run

rooster and now we have what we want so

this is the second use case you might

have for this pointer through setters

let's use the parameter that is named

the same as your member variables so

we're going to set up all the other

setters we're going to set up a setter

for the breed we're going to say std

strength view and it's going to be breed

we can do that because now we have tools

to really do this properly we're going

to say this breed and we're going to say

equals read this is going to do and we

can set the age and we're going to say

dog age and we're going to pass in a

value and we're going to go inside what

is it called it's called ph i don't

think it makes sense to call the

parameter ph because it's not a pointer

so we're going to go inside and just the

reference of a pointer so we're going to

and we're going to say this so we're

going to go inside and say this ph

equals h i think this is going to work

and we need to reference this pointer

because what we have as a member

variable is the pointer so we need to go

through the ugly syntax you see here and

this is going to set our age so we can

go through this and really change the

information so we're going to change the

breed here set dog breed let's go down

and choose that and we're going to say

wirefox terrier and we're going to go

down and set the age we're going to say

guilt 1 set dog age and we're going to

say for why not so we change the

information of our dog through our

setters here and we're going to print

let's build again we're going to use gcc

for that the build is good we can clear

and run rooster this is going to give us

new information for the second print

here so name is going to be pumba breed

is going to be wirefox terrier and age

is going to be four and we have the

information for our dog object here okay

now we have this and we want to see how

using the this pointer and in this case

we will be using pointers let's change

our setters to return dog pointers we

can do that and we're going to go down

to say to dog breed we're going to

and we're going to go to set dog age and

we're going to return a dog pointer now

after we do this we will need to return

these pointers and we're going to go

inside and say return this remember this

contains the memory of the current

object so we can return this and fit

that to a returned pointer so we can go

down in all the other functions and

really save this we're going to say

return thus we return the memory address

through the setters that we are doing

here we're going to return this

and after we do this we can change the

setting we are doing here to b1

statement and we can comment this out i

think we can do that and what we're

going to say is dope one and we're going

set dog name and we're going to pass in

pumbaa but this is going to return a

pointer now set dog name is returning a

pointer to the current object and you

can see that here this is what we are

returning so we can go through this

pointer and call some other functions

for example we can say set dot breed

directly and the visual studio code is

going to figure out that what we are

returning is a pointer and it's going to

change our access notation here to a

pointer axis notation and we're going to

use this in one single statement so

we're going to put in our breed and

we're going to call the function to set

the age okay you see that it uses

pointer access notation and this is

really cool so we're going to put in our

four and you're going to see that this

actually works and this is really cool

if you don't want to do thanks in three

steps you can give your users the option

to do things in one step using returned

pointers like this and this is really

cool i use this all the time for my

classes that i design in my applications

so if we're both we're going to see that

the world is good and we're going to

clear and run rooster we're going to see

that the information is n name is pumbaa

breed is waterfox terrier and the age is

for and we were able to do all these

changes in one go so we can even change

this to use references here we are using

pointers so let's say that we are using

pointers but we can also use references

let's go on top here and say that this

is using pointers and we're going to

comment this out but before we do we're

going to copy all this because we're

comment all this out and we're going to

go down and say change calls using

references and we're going to go down

and put in our code and we're going to

change our setters to return references

instead of pointers we can do that so

we're going to change the star here to

an ampersand symbol here and this is

going to do the magic so we have a dog

reference returned from all these

functions so because we are no longer

returning a pointer returning this

directly is going to give us a compiler

error we need to dereference this

pointer and get to what what is pointed

to now the compiler will know that we

are returning a reference to the current

object and this is the syntax we can use

to do this let's go down and dereference

all the returned pointers and if we go

down we're going to see that this is

good already and we can go down and set

up our chained call using references and

we're going to go down and say dog one

we're going to set dog name and we're

what we have been doing all along now

we're going to use the dot access

notation because what we are returning

is a reference and you're going to see

that visual studio code is going to pick

this up the breed is going to be wirefox

and we're going to say set dog age and

we're going to pass in our four and

you're going to see that this is valid c

plus syntax and if we print the

information we're going to have new

information applied to our dog object

here we can weld and see that this is

actually working you see the world is

good we can clear and run rooster and

we're going to see that information has

been applied to our dog object so these

showing some of the usefulness for the

this pointer we have seen that we can

use the this pointer to print the memory

address of the current object if we go

down and look at our constructor and the

destructor we are printing the address

of the current object in our debug

statement here and this is really cool

we can use the this pointer to resolve

conflicts in our setters for example we

can use a parameter that has the same

name as the member variable and it's not

going to be really confusing and lead to

bad results it's going to change the

actual member variable and change it to

whatever you pass as the parameter and

this is really cool we can also use the

this pointer to set up change calls for

our function and we have seen that we

can do that either through returning

pointers like we are doing here and

using the this pointer as a return

object for our function here or we can

use returned pointers to do this and if

we do that we're going to be able to

call our functions in one go like we are

doing here using pointers or do the same

thing using references like we are doing

here this is really all we set out to do

in this lecture i hope you found it

interesting we are going to stop here in

this one the next one we're going to

learn about struct go ahead and finish

up here and meet me there in this

lecture we're going to learn about the

struct keyword and this is another

syntax you can use to create classes in

your c plus plus program we have seen

that we can already use the class

keyword to create our classes i have to

break it to you that we can also use

struct to do the same so the syntax here

is going to create a class called cat

and it's going to have a member variable

called string name the difference

between struct and class is that for

classes members are going to be private

by default and when you do something

like this and create class objects you

want to be able to access the name here

directly for example from the main

function if you do that you're going to

get a compiler error because class

members are private by default but if

you use struct members are going to be

public by default and you will have

direct access from the outside this is

the only difference between class and

struct otherwise you can use them

interchangeably and they are going to do

the same things we have been seeing for

classes they really are the same things

the only difference is that classes are

going to have private member variables

by default and struct will have public

member variables by default but we can

change this defaults by putting in our

own public and private sections inside

our class so for example here you see

that we have changed our dog class to

have a public member variable through

the public keyword here and we can do

the same for cat for example we can put

in a public section and a private

section and it's going to behave like

classes we have been welding so far

one common use we have for struct is

when we have to set up classes that only

have public member variables for example

you can need to set up a point

model in your c plus plus program and

you can set up a class like this you can

say struct point you're going to put in

the member variables and they are going

to be directly accessible from the

outside and this is something you will

see a lot out there so this is really

all about struct we're going to head

over to visual studio code and play with

us a little more okay here we are in our

working folder the current project is

struct we're going to grab our template

files and we're going to put them in

place struct that's all project here

and we're going to open this in visual

let's grab extract and drag and drop on

top of visual studio code here this is

going to open our folder we can now open

the main cpp file and clean things up a

little bit okay so we're going to set up

a simple class called dog we're going to

say class dog and inside we're going to

have a member variable called name it's

going to be an std strand let's say dog

name or m name to mean that it is a

member variable this is a syntax you

will see a lot in c plus plus out there

so let's use this from now on we're

going to say m name and we're going to

have another class let's put our

semicolon we're going to use struct to

set up another one and it's going to be

called dog let's call this cat and we

are going to go inside and set up our

member variable we're going to say std

strength m name and it's not going to

have anything m so if we create objects

of these classes and try to access them

we're going to see the fundamental

difference between structure and dog

let's create a dog and we're going to

say dog one and we're going to create a

cat and we're going to say cat one and

if we do dog 1 and try to access the m

maybe set it to something else let's say

fluffy we're going to have a compiler

error because members of a class are

private by default and we can't really

so we are trying to access something

that is private from the outside we're

going to get a compiler error okay so we

have a squiggly line here but if we try

to do the same for a cat it's going to

go through because cat is destruct and

members of structs are public by default

let's do that and really show you this

we're going to say cat1 and we're going

to say m name and we're going to give it

a name and let's say johnny i am making

this up i don't know if there is any cat

named johnny but we're going to use this

and you're going to see that we don't

have any squiggly line we're going to

build and see if gcc is going to take

this it's going to take it the world is

good we can bring up a terminal and run

the program and we're not going to see

anything because we're not printing

anything from the main function here but

if we want we can print this name of our

cat we're going to say sddc out and say

cat one name and if we build we're going

to see that so the both should be good

it is good we can clear and run rooster

and we have johnny printed out and this

is the name of volca and this is really

the difference between class and strut

members of classes are going to be

private by default members of struct are

going to be public by default but we can

change these defaults for example let's

make everything public we can do that no

and we can move this a little bit to the

right so that things are aligned nicely

and we can do the same for struct okay

so let's align this now if we do this we

will be able to go in the main function

and say dog name and change that and

we're going to be able to see that if we

print that out so let's go down and say

stdc out and say dog1 name and print

and if we build now we're going to see

the name of our dog printed out okay

well this is good we can bring this up

and clear a little bit and run rooster

we're going to see fluffy our dog name

and johnny our cat name so this is

really all about classes and struct they

are the same things but the only

difference is the defaults that come

with these things but the common use we

have for struct is when we want to set

up a class that only has direct member

variables and we don't intend to put

methods into that class a good example

of this is the struct off point so

suppose we want to model points in our c

plus plus program so we can do something

like this and a point is going to have

two coordinates x and y we're going to

say double y and from this point on we

will be able to create point objects and

print them out however we want so for

example we can go down and say point

point one and from this point we can go

in and say 0.1 and say x and assign a

value to x let's put in a 10 and we're

going to go down and say point 1 y and

we're going to give it a value let's put

55.5 why not and we can do whatever we

want with this point for example we can

set up a function which is going to

print a point we can do that let's say

void print point and we're going to pass

the point by value or we can even use

references because this is going to be

an object const point reference i think

this is going to do and we're going to

go inside and print the information

hddc out point and we're going to put

the coordinates on we're going to say x

is going to be point x and y is going to

be point y why not and we're going to

put in our closing square bracket and

to put a new line character after our

print here now we can go down and say

print point and pass on point one

and if we do that we're going to build

and we're going to do that through gcc

you see the both is good now if we print

we should see the information about our

we can go down and change the

information about our point for example

we can copy this and go down and change

2.7 why not and if we print the

information about our point we're going

to see that we have new information and

we're going to print point one and

therefore world we're going to see the

new information so the build is good we

can clear and run rooster now you see

new information in our point so this is

really the difference between class and

struct the only difference is going to

be in the defaults and struct is mostly

useful if you want to set up classes

that only have public member variables

and you don't really want to use

functions or methods in that class and

we have an example of that here and if

you have a case like that you will use

struct your code is going to be much

easier to read and understand from the

perspective of other c plus plus

developers we are going to stop here in

this lecture and the last one we're

going to learn about the size of objects

go ahead and finish up here and meet me

in this lecture we're going to learn

about sizes of class objects and try to

what are we going to see if we try to

print the size of our class here called

wrapper inside we have two member

variables which are of and type

and we have a member variable which is

of std string type what do you think

when we print the size of this wrapper

try to think about it so what c plus

plus does it's going to only account for

the size of your member variables so

it's going to add to the sizes of these

guys in memory so we know an end is

going to take four bytes in memory so

we're going to have eight bytes for

these two ants and we're going to have

an unspecified amount of memory for a

strength because a strength is

internally implemented as a class and it

stores its data as cost car pointers so

and the size of an object doesn't really

account for thanks you are referring to

using pointers it may count to the size

of the pointer itself but it's not going

to count what is pointed to and in the

case of string for example we really

the range of things that we are pointing

to so we're not going to have correct

information with hdd string here but in

general the size of an object is going

to be the sum of the sizes of its member

variables the functions are not going to

be counted then the functions are just

helper functions that live somewhere in

memory but they're not going to be

accounted for in the size of your object

another reason you might think functions

are not accounted for in the size of the

object is that really functions are

affiliated with the class itself

functions are not affiliated with class

objects the class is going to be the

blueprint from which we're going to

generate thousands of objects if we want

but the functions or the methods are

going to be associated to the blueprint

itself so it really wouldn't make sense

to associate the size of those functions

in memory to class objects now that you

have this idea let's head over to visual

studio code and play with this a little

more okay we have saved that the size is

mostly going to be the sum of the sizes

for the member variables but this is not

always correct because of a phenomenon

binary alignment is a thing most

compilers do when they have member

variables of different types and member

variables that have the size of four

bytes in memory are going to be stored

at memory locations that are multiples

of four and because of this phenomenon

we might have gaps between our memory if

we have variables for example that are

of two bytes in memory and four bytes in

memory and we're going to have gaps

inside and the size of the object is

going to be slightly off the sum we

might do for the sizes of our object i

realize this may be confusing we're

going to head over to visual studio code

and we're going to see a few examples

okay here we are in our working folder

the current project is size of class

objects we're going to grab our template

files pretty quick and we're going to

put them in place and we're going to

open our project in visual studio code

by dragging and dropping here we have

our main cpp file we can close the left

and we can clean the main function here

we're going to set up a simple class

let's call this dog why not we have been

using dove so let's use this again

we're going to put our closing semicolon

we're going to put a public section and

it's going to just contain a constructor

and we're going to say dog and we're

going to use the default and we're going

to put in a private section and

in here we're going to put in a size t

this is the leg count of the dog why not

let's say we are modeling this okay so

now we have our dog class in place we

can create objects of this dog class

dog one and if we do this we are

interested in knowing the size of our

so we are going to say stdc out size of

dog and save that and uh fingers crossed

we're going to see the size of our dog

object here and try to guess what we're

going to get in the slides we have seen

that the size is mostly going to be

the sum of the size of the member

and let's print the size of size t here

because size d is our only member

variable so i think it's going to be

helpful to see its size printed out

so we're going to have some context if

we do that we're going to say size of

save that and we're going to build this

program let's do that we're going to

pass this through gcc you see the both

and we're going to bring up a terminal

and run this see what happens okay we

see size of size t is eight and the size

of our dark object is eight and this is

really cool because we see that the size

of our class object is really the size

member variables that we have in here

let's set up another member variable and

really show you this so we're going to

have arm account okay so we are just

i don't aim for this class here to make

some sense practically we just want to

see how the member variables affect the

size of our class object now we have two

member variables and we're going to try

and world we're going to use gcc to do

that and we're going to clear and run

now you see that size of doug is 16 and

proven that the size of an object is

only accounting for the sizes of the

member variables it's not going to count

the functions that we have here so if

for example we had a function that says

printful and we have another one that

says do something this is not going to

change the size of our object because

functions aren't accounted for in the

so let's build and really show you this

the world is good we can clear and run

rooster we see that we have the same

sizes the size of dog is 16 the size of

size t is eight we can even use object

names here for example we are using the

class itself but we can use dog one here

and we're going to get the same

information let's both and we're going

and you see that we have the same size

so if we change this thing to put in a

pointer we're going to see something

else let's put in an end pointer

and let's say ph like we have been doing

all along and see what we get and we

know that the size of a pointer on my

system let's print that out so that we

have no doubt let's for example say size

of end pointer is going to be size of

end pointer okay let's build we're going

pass this through gcc and the both is

going to be good we can clear and run

rooster we're going to see that we have

24 because we have two member variables

that are going to be eight bytes in

memory of size t they are of type size t

and we have a pointer which is going to

have a size of h in memory but we don't

care what this pointer is pointing to

if for example this pointer is pointing

we don't care we're just going to

account for the end pointer here and

this is really phenomenal because if for

example we tried to set up an sdd string

and by now you should know that std

strand itself is implemented as a class

in c plus plus so it's really a class

and we can print its size so let's set

up a string object here we're going to

say std strung and we're going to say

name and we're going to initialize this

with hello world okay we're going to see

something really strange here so if we

print the size of name here we're going

to say size of name and we're going to

print that let's see what we get we're

see the block is good and can clear and

run roaster we're going to see that size

let's change the text inside our string

and see that we change accordingly

because this can really be confusing

let's say i am the king of the universe

why not and we're going to build again

let's see what we get fingers crossed

this is going to blow your mind you see

we have the same size for name even if

we are changing the text in here so what

is really happening the strength is

storing our text here as cost card

and what we have is a pointer inside and

is a member variable which is a pointer

like we have here so what we will be

accounting for in the strength class is

the size of the pointer but it's not the

size of what is pointed to okay so the

car pointer may be pointing to thousands

of characters in memory but as long as

the compiler is concerned it's just

going to use the pointer member variable

and it's going to account for it in the

size of your object hopefully you can

the size of our string objects is going

regardless of how large is this strand

this is really something you need to

understand otherwise this is going to

throw you off as you design your c plus

plus applications and this is really all

i had to share in this lecture the size

of your object is mostly going to be

member variables you have and the size

is going to be the sum of the sizes of

your member variables i would like to

welcome you in this new chapter where

we're going to be learning about

inheritance and inheritance is a feature

to allow us to build classes in terms of

and what i mean here is that we can

build complete hierarchies of classes

that depend on other classes for example

if we think of a person as a type we can

have different types of persons we can

have a doctor a doctor is a person we

can have a physician a physician is a

person we can have an engineer an

engineer as a person we can have really

all kinds of persons and we can capture

these kinds of relationships in c plus

plus using inheritance for example here

we have an inheritance hierarchy we can

set up a person type in our c plus

program and put in whatever member

variables we need to define a person for

whatever purposes we are building our c

plus plus application for once we have

this type we can build other types that

depend on this person for example we can

build an engineer type which is really

going to embody the person type inside

so what we will be doing is really

setting up a layer of a person type and

in our engineer type which is going to

depend on person we will boil the novel

layer on top of that and really reuse

that person type without having to

rebuild this from scratch hopefully you

can see that this is going to improve

code reuse we can also reuse this

engineer type and well the other types

on top of it for example we can have a

civil engineer we can have an electrical

engineer we can have all kinds of crazy

engineers modeled in our c plus plus

using the inheritance and this is going

to be really cool so this is what we are

going to be exploring in this chapter

looking at the facilities that c plus

plus provides to capture these kinds of

relationships in our c plus plus

programs please note that inheritance is

a really big feature and it is a

defining feature of object oriented

programming c plus plus object oriented

programming is a paradigm or a way of

thinking about programming that uses

objects and the most basic defining

feature of object oriented programming

in c plus plus is classes that we have

learned about using classes we can

define things for example we can set up

a car we can set up a house we can set

up a spaceship we can do all kinds of

crazy things with classes and ziplocs

plus inheritance is going to build on

top of classes and allow us to build

classes that depend on each other and

hierarchies that are going to make our

design much easier to look at and

understand and work with okay so this is

what we are up against in this chapter

learning about inheritance and really

exposing you to as much as possible to

let you use inheritance in an easier way

in your c plus class programs we are

going to start in the next lecture and

try out inheritance for the first time

go ahead and finish up here and meet me

there in this lecture we're going to try

out inheritance for the first time in

but before we do that let's remind

ourselves of what inheritance really is

inheritance is a feature we have in c

to be able to build new classes in terms

of the classes we have predefined

and the new classes are going to be

stealing features from the already

pre-existing classes if i can say it

like that and the more classes we build

in terms of others we're going to end up

with what we call an inheritance tree

which is basically going to go from the

top to the bottom with the most

fundamental class on top and the derived

class at the bottom here we have a

simple example for example we can have a

defining the basic features of a person

but based on that personal class we

might want to derive other classes that

build on top of this person class for

example we might want to define an

engineer and a doctor and we know that

an engineer is also a person so they are

going to inherit some features from the

person class the same goes for the

doctor class it is going to inherit

some features from person but all these

derived classes are also going to add

their own features to the person class

siplus plus allows us to build these

here is another simple example we have a

vehicle class to the top of our

inheritance hierarchy and below this

class we might derive a track class

which is also a vehicle we might have a

minivan we might have a truck we might

have a pickup truck we may really do all

kinds of crazy vehicles which are going

to inherit the basic features from the

vehicle class and add their own

on top of the vehicle class so this is

the basic idea behind inheritance in c

plus plus so the examples we're going to

so here is a simple example of what

we're going to do in this lecture we're

going to set up a person class which is

it is going to be defining two member

variables which are going to be of std

string type we're going to have a last

name for the person and the first name

we are going to derive from this class

the player class is going to inherit

these features from the person class so

it is going to have a last name and a

first name built into it but that's

going to be our base or our starting

point we are going to add to this base

and add another member variable from

player and we're going to be having the

player class which is really a person

but it is going to add things to person

to customize on what we can do with a

that we wouldn't originally be able to

do or have with a person class this is

the basic idea okay now that we know

this we're going to set up our personal

class which is going to be our base

class it is going to have our two member

variables first the name and last name

we're going to have a bunch of

constructors and we're going to have a

stream output operator to be able to

print this on the console and see our

information here nothing special but now

that this class is done we can build

other classes on top of this class so

what we can do for example we can derive

so the syntax is what you see here we

say class player we say column column

and specify the class that we are

inheriting from so the parent class for

this class is going to be person or in

other words we're going to be deriving

from the person class and we're going to

be doing that publicly okay for now i

don't want you to worry too much about

this public keyword we're going to be

learning this in steps just know that

this is the syntax you use to derive

now the moment we do this the player

class is going to have the person

information embedded inside but we will

also have the ability to customize or

at the level of the player class this is

what we do we have a private member

variable and it is going to specify the

game at the player place we're going to

have our own set of constructors we can

really build player objects but they are

going to have a person part inside that

is going to store information about this

you notice we don't have a member

variable here for the first name we

don't have a member variable here for

the last name but that information is

going to be baked into this player

object and this is really how

inheritance helps us out we can derive

and build on top of them without having

to redo the fundamental work to build

our base classes we can just build on

top of them and really do things faster

and more efficiently okay so here are a

few things you need to know about the

public inheritance that we just did and

we are saying public inheritance because

public person this is doing public

inheritance and we're going to see what

this gives us so with public inheritance

derived classes can access and use

public members of the base class

but the derived class can't directly

access private members from the base

class i want you to let this sync end

what this means from the player class we

can't directly access the private member

variables we had in person remember our

first name and last name are private to

person and we can't directly access them

in any deriving class that is doing

public inheritance okay so in our player

class if we try to access the first name

and the last name we're going to have

compiler errors because we can't

directly access them but not to worry

here we can still go through

the public getters that we have in the

to access the private member variables

from the base class and that's what

we're going to do in this lecture here

because we don't have access to more

powerful tools we're going to learn

about in the next few lectures the same

is also going to apply to friends of the

they are going to have access to private

members of the derived class but they

the private members of the base class if

you try to access the private parts of a

from a friend of the derived class

you're going to have a bunch of compiler

okay now that you know this we're going

to head over to visual studio code and

play with this a little more and really

here we are in our working folder the

current project is first try on

inheritance we're going to grab our

template files and put them in place

and we are going to open this in visual

studio code pretty quick by dragging and

dropping here let's do that properly and

we're going to have our main cpp file we

can clean this up a little bit and we're

going to add our classes the first class

we're going to add is the person class

so we are going to create its header

file and let's do the cpp file i am

going to grab the code i have lying on

my drive for the header here i am going

to put the class in we are including the

classes we're going to need we need

string and io stream here because we're

going to be outputting thanks through

and down here we have our two member

variables we have first name and last

name they are of std string type and we

have a bunch of constructors here a

default constructor and one that takes

two parameters we are taking them by

copy here this is bad we should at least

pass them by reference here let's

and we're going to make the second one a

reference as well let's do this and we

have a destructor which is going to do

nothing because we really aren't doing

any dynamic memory allocation here we're

going to head over to the cpp file and

put in the code for that we're going to

include the person and we're going to do

implementations i should say and we're

going to pass our parameters by

reference again let's do this and our

constructor should be done now we have a

person class that we can use to derive

other classes and use this class as a

foundation to build other classes to

visualize this again our class person is

going to be the base class for our

so if we build a player class it's going

a person part of it which is going to be

the foundation on top of which we're

going to build notice that in player we

don't need to set up last name and first

name they are going to come from our

personal part of player all we need to

do in player is set up the game member

variable to make him a full player who

can have the game they happen to be

playing this is the idea here okay so

now that we know this we're going to put

in our player class we're going to

create the files for it let's do player

dot h we're going to put this in and

that cpp we're going to put him and

we are going to hop over to the header

file and put in our code the class is

going to be player and it is going to be

inheriting from person this is the

syntax again we say colon colon we say

the kind of inheritance we want to do in

this case it is public and then we say

the class that we are going to be

inheriting from from this point on the

player class is going to have a person

part of it and we are going to prove

this in a minute when we run this code

here notice that we can build player

objects by just passing in the game

parameter here which is going to be used

to initialize our member variable let's

also make it a reference because this is

good practice it is going to avoid

copies you can even use string views but

that's going to be your choice

we are going to hop over to the cpp file

and put in our implementation

and this is going to complete our setup

for the player class which is going to

be inheriting from our person class here

we can actually head over to the main

cpp file and include the player class

let's do this we're going to say player

and we can create player objects let's

look at the code again for a player we

have a constructor which is going to

take a string parameter we can use this

to create a player and specify the game

for now we don't have enough tools to

put in the data that would initialize

the member variables in the base class

which is person here if we go back to

person we're going to see that we have

the first name and the last name

these member variables are going to be

inherited because a player is inheriting

from a person this is the syntax to do

that but even if the player class has a

person part inside of it we can't really

access private members from person

from a player object we're going to see

a few ways we can get around this and

one of those is to go public methods

from the person class to access

private parts of the person class this

is going to give us access to these

member variables if you go down in our

stream output operator you're going to

see that we are using these getters here

the parameter is a player objects that

we want to print out but to get access

to the names we are getting the first

name and the last name through our

getters here before we really explore

this any further i think it is a good

idea to go in the main cpp file and

create a player object so we're going to

do that we're going to say p1 and we're

going to specify that they play

basketball why not okay so we have our

and we can really do all we want with

that for example we can print the

information about this player object if

you remember in player we have a stream

output operator which is going to print

and here we have a problem because this

guy is taking the data by reference

and this is not a reference this is a

temporary object that we are passing

so we could go back and change this to

take a string view parameter

let's go back and do that we're going to

include a string view here in player and

we're going to change our parameter to

be std string view by value and we're

going to do that in the cpp file let's

do that we're going to say std string

view and this should take care of our

problem here you see that the problem

goes away now that we have this guy we

can print it out we can say sddc out

player and i put the information out

okay so now that we have this we cannot

try and build our program we're going to

our favorite compiler and you're going

to see that we have a problem undefined

reference to player destructor let's go

back in the header and see that we have

a destructor but we probably didn't put

a destructor in the cpp file so let's do

that or because we're not doing any

dynamic memory allocation we can even

completely take out this destructor and

we're just going to use the one the

compiler generates for us this is going

much easier to handle in our code so we

can build again with gcc okay the world

is good we can run this program

and let's see if we have a powershell

window we don't we're going to bring up

a new one and we're going to run rooster

we should see information about our

player so player the game is basketball

the names are mysterious person because

that's the default data we inherit from

a person if you go back to person you're

the default data in first name is

mysterious the default data in last name

is person and it is what we see printed

in our powershell window when we print

information about our player object

another thing i want you to see is that

that any player object is going to have

backed in and that's going to be storing

the information that is modeled into our

person class and we can use a debugger

to do that for this to work i am going

to put a break point here on line 8

which is printing things out

this break point is going to be hit

after our object is set up and we can

really see the data inside this guy here

so what we're going to do we're going to

and we're going to use g plus plus we're

going to use the debugging tools that

come with gcc because this is our

favorite we're going to hit the green

this is going to start our debugging

session a binary is going to be built

and it is going to be plugged into our

debugger and we're going to hit a break

now if you look on the left here you're

going to see a title that says locals

we're going to expand this and we're

going to see that the p1 object actually

has a person part of it and you see that

visual studio code is being helpful here

it is saying that this is the base class

and if we expand we're going to see that

we have our member variables we have

first name and last name and this is a

player object that we are looking at

don't forget that and on top of our

person part we also have our own member

variable which is the game that we play

and it is right here hopefully this

that any derived class object is going

to have a base part embedded into it and

that's going to be the foundation on top

of which the derived class is going to

be building its own tank this is the

basic idea here okay now that you've

seen this we're going to kill our debug

and we're going to see some of the

things you need to be careful about when

doing public inheritance like we are

doing here the first thing i want you to

see is that you don't have access to

of the base class if you go back to

let's kill this so that you're not

confused if we go back to our personal

class we're going to see that our first

name and last name are private

so they want to be accessible to any

that does public inheritance like we are

doing here they are just going to be

private they are going to be part of the

class but the derived class would have

access to them this is the idea here and

if we go in our output stream operator

and comment out what we have here and

try to directly access these member

variables let's do that i am going to

copy the code here and put that on top

and we are not going to go through the

getter methods from the base class we

are going to try and access m first name

let's go back and look at the names for

the member variables it is first name

and last name let's use that we're going

to say first name you see that through

intellisense but trying to access that

is going to give us squiggly lines you

see that we have this in our

autocomplete but we have squiggly lines

we can't access these if we try to

compile our program let's do that again

we're going to use gcc and we are going

to get compiler errors and the compiler

errors are basically going to say

first name is private within this

context again the meaning is that

first name is private to the base class

and we have no business accessing that

the player class here this is the

meaning so we can't really access that

okay i realize this is a global function

but even if we try to do that from a

member function let's do that from

a constructor we're going to try and say

first name okay i realize the access we

are trying to do from the output stream

operator is really not a good example

because this is not a member function it

is a global freestanding function so we

can try and change the first name and

last name from the constructor for

example and we're going to see that this

is not going to work either so we can

take this out and we're going to

remove our block comma so we're going to

take out what we just did here

and we're going to uncomment our good

code here which is using getter member

functions from the base class and we're

the first name and last name from the

base class and change those into our

constructor of the derived class we're

going to try and change for example the

first name and make it john and we're

going to take the last name and change

snow let's do that and let's go back and

make sure we have the correct names

and you see that we have squiggly lines

we can't really do this because these

are private members of the base class

and we can't access them from a derived

class they are part of the player class

which is a derived class but we don't

have access to them we can't modify them

or do anything we can't read from them

we can't write from them this is the

message here if we try to build our

program we're going to use gcc to do

we are going to get compiler errors and

uh let's see the compiler error we get

again the error is that first name and

last name are private to the base class

and we have no business accessing them

from a derived class like we have here

so if you need any kind of access to a

member of the base class you will have

something that is public and a good

example is getter methods which are

change things so for example if we want

the ability to change the first name and

the last name we can set up a bunch of

setter methods let's do that we're going

to say setters and we're going to say

first name and we are going to pass an

let's do that we're going to say string

this is going to modify our class so we

are not going to mark this as a custom

member function and we're going to say

we are going to set up a setter for the

last name set and we're going to pass a

string view here and we're going to say

ln for the last name again this is not

going to be a cast member function so

we're going to say last name and we can

pass in ln as our new name here now that

we have these end we can take out

these things we have in the constructor

i think the job for this is done and

this is going to give you compiler

errors and we can go in our main cpp

file and change the names for this

person here for example we can say p1

first name we're going to pass john and

we can also set to the last name we're

last name and we're going to pass snow

and this is going to do if we build and

run this program we're going to see that

the world is going to be good this is

and if we run we should see the

information printed out we want to join

snow printed out and the game should be

let's clear and run rooster we're going

to see that the data is in here the name

the names are jon snow and we have our

game to be basketball here but notice

these are base methods and we are

calling them from a derived object and

this is living proof that the public

members from the base class are going to

from a derived class that does public

inheritance like we are doing here and

this is really the main message you can

inherit publicly and have access to

public stuff from the base class and use

them in your derived class but private

data is going to still be private to the

base class you can't use that in a

derived class this is the message here

and this is really all i wanted you to

see in this lecture the big thing is to

notice the syntax you use to do

inheritance and if you do this the

player class is going to be derived from

and it will have a person part

baked inside and we can build on that

foundation and for example put in our

own member variables and do all kinds of

public stuff from the base class are

going to be inherited and usable from a

derived class we just saw that by

setting up a bunch of setters that live

in the public scope of the base class

and they were usable from the outside

because they will be inherited as public

in a derived class so we can really call

these methods and use them from the

outside like we are doing here but

private data from the base class is not

going to be accessible and usable from a

derived class and we saw that by setting

up this piece of code in the constructor

of player this is going to give us a

compiler error saying that first name

and last name are private to the base

class we are going to stop here in this

lecture in the next one we're going to

learn about another kind of access

specifier we have in c plus plus and

so go ahead and finish up here and meet

in this lecture we're going to learn

about the protected access specifier you

can use in your c plus plus class

and we're going to be reusing the same

example from the last lecture we're

going to have a person class which is

going to act as our base class and we're

going to be deriving from this person

and creating a new class called player

the player class is going to have a

and we can use this as a foundation to

build other fans in player class for

example we can set up our own member

variables and do all kinds of crazy

things and this is the setup we used in

the last lecture we set up a person

class and our members were private as

you saw here but in the last lecture we

private member variables are not going

to be accessible and usable from derived

classes that do public inheritance and

sometimes we want members from the base

class to at least be accessible and

usable from a derived class but still be

inaccessible from the outside and we can

achieve this using the protected access

specifier so for example we can change

the access specifier of our member

variables from private to protected and

at the moment we do this we will be able

to access for example read from and

write into these member variables from

derived classes so for example we will

be able to modify these guys from a

constructor of the derived class and we

thought that that was impossible from

the last lecture but still we want to be

able to use these from the outside of

our derived class which is person here

so we're going to still do public

inheritance like from the last lecture

but now that our member variables in the

base class are protected we will have

the ability to do whatever we want with

them in the derived class and when we

say in the derived class we mean from

any method from the derived class for

example we can go in our constructor

here and then set data into the member

variables from the base class and that's

going to work as we're going to see

in a minute now that you know this we're

going to head over to visual studio code

and play with this a little more okay

again our member variables from the base

class are going to be protected

okay so we can really say that here

let's say protected and at the moment we

do this they are going to be accessible

and usable from a derived class so from

the derived class we will have the first

so from the derived class we will have

our members baked then we will have a

last name and the first name and because

they are protected in the base class and

we are doing public inheritance we will

be able for example to set data into

these member variables from a derived

really cool now that you know this we're

going to head over to visual studio code

and play with us a little more okay so

here we are in our here we are in our

working folder the current project is

protected members we're going to grab

the code from the last lecture and reuse

that because that's going to have our

inheritance hierarchy already set up we

will have our person and player class

and we can reuse them we will have our

person and player classes and we will

reuse them without needing to completely

set them up from scratch that's going to

save us a few seconds so we're going to

and we are going to open this little guy

in visual studio code by dragging and

dropping here and we will have our

person class which is going to be the

base class it's going to have our member

variables which are going to be private

from the last lecture we will have a

player class which is going to be

inherited publicly from the player

we will have a player class which is

going to be publicly inheriting from

person and we have our main cpp file

which is going to set up a player object

and try to use it and we're going to see

how this goes in this lecture so what we

want to do is to change the access

specifier in the base class and make

that protected we can do that we can say

protect it and this is going to change a

few things about this class what this is

if you do public inheritance from this

person class you will have the ability

to do whatever you want with these

member variables from a derived class

you will have the ability to write into

these member variables and change the

data that we have inside you will also

have the ability to read from them and

that's something we couldn't do from the

last lecture and this may come in handy

sometimes another thing you should know

is that these members are still not

going to be accessible from the outside

so from the standpoint of the main

function for example here they are going

to behave as if they are private because

they want to be accessible from the

outside they will only be accessible and

modifiable from derived classes

that do public inheritance this is

really important to understand now that

we have this we can really do all kinds

of crazy things for example we can go in

our constructor of player and comment

what wasn't working from the last

lecture and this is going to work now so

let's uncomment this and we're going to

see that the squiggly lines are going to

go away and if we build a player object

using this constructor we're going to

see that we're going to have jon snow in

even if we don't set using the setters

from the base class so we can take these

and if we print information about this

player we're going to see the game to be

basketball and the names are going to be

john snow because we are setting up this

in the constructor of player that's no

longer that's no longer going to be the

data we get from the constructor of a

person object which was here

in the base class let's try to build and

run this program so that you can really

see this i just used clan here but it is

also going to work no big deal here the

build is going to be good we can clear

and bring up a powershell window we can

use to run this program we're going to

say rooster and you're going to see that

having the information the game is going

to be basketball the names are going to

be jon snow and we are setting this data

from a derived class and we have the

ability to do this because these members

are now protected in the base class so

they are accessible and usable from a

now that we have this ability we can

really change how our class at least the

derived class works we're going to

change it to have two more parameters

and we're going to pass the first name

and the last name and pass this data

back into the base class by setting the

data in the body of the constructor this

is going to work so let's add our

parameters we're going to say std string

first name param and we're going to put

in another one which is going to also be

a string view parameter and it's going

to be last name param we can say that

and we're going to hop over in our

implementation let's grab what we just

added because we will need to put that

in our cpp file we are going to go in

player.cpp and we're going to add this

data we're going to put that here

we can close the left sidebar to have

some more breathing room and then we're

an initializer list here because this is

really going to be useless we are

changing data in the body anyway so what

is say game param or a game and we're

gamipuram i am really sorry i am not

following the same convention for the

naming of my member variables but we can

change this later so let's say first

name we are going to pass in first name

ram and for the last name we're going to

say last name param and that's going to

do now we have the ability to go in the

main cpp file and create player objects

and specify the first name and the last

name and this is going to be much more

flexible so let's go back to the

constructor and see the order of our

parameters game first name last name so

we can come here and say first name is

john and the last name is going to be

snow and if we build and run we're going

to see the information printed out here

and now we have the flexibility to be

in a constructor and this is going to

make the job of building our objects

much easier and we can forward this data

back into the base class using the

protected mechanism that we just learned

about in this lecture and this is really

cool so let's build we're going to pass

this through gcc and the world is going

to be good we can clear and run rooster

we're going to see that the data is

passed back to the base class this is

really well okay so this is really all i

wanted you to see in this lecture we can

set up protected member variables and

they are going to be accessible and

usable from any derived class that does

public inheritance but they want to be

accessible from the outside so if you

try and for example say p1 and say

first name and try to change that to

something else let's say daniel for

example you're going to have compiler

errors because this is not going to work

so let's try and build and show you the

compiler error okay so protected members

are not accessible from the outside

they will be just accessible from

derived classes or to be more specific

they are going to be accessible from

the members of the derived class and by

members i mean member functions because

that's where you will be accessing and

modifying stuff so let's go back to the

main cpp file and remove this

and this is really all i wanted to share

with you and i hope you found this

lecture interesting we are going to stop

and in the next one we're going to zoom

in on the syntax here we are using to

derive from other classes we just did

the public inheritance here but in the

next lecture we're going to see that it

is possible to actually do protected and

private inheritance and we're going to

see what this means in the next lecture

so go ahead and finish up here and meet

me there in this lecture we're going to

learn about base class access specifiers

and in case you didn't know we have been

using base class access specifiers in

this chapter all along and to really

understand this let's look at our player

class which is inheriting from person

and we are doing public inheritance the

public keyword here is a base class

access specifier and it is going to

how accessible our base class members

from a derived class and we have three

options okay so if we do public

inheritance like we see here in our

anything that is public in the base

class is also going to be public you see

m1 here is also public in the derived

anything that is protected is going to

stay protected and anything that is

private in the base class is also going

to stay private in the derived class

try and take a moment to look at this

the member access specifiers we have in

the base class are going to stay intact

public inheritance again anything that

is public in base is going to be public

and derived anything that is protected

in base is going to be protected and

derived and anything that is private in

private in derived this is one kind of

inheritance we can do in c plus plus but

we can also do protected inheritance and

the syntax to do that you just use the

protected keyword here you say class

player column column and specify that

you want to do protected inheritance and

then you specify the base class you want

to inherit from the moment you do this

anything that is public in the base

class is going to be protected in the

anything that is protected is going to

stay protected anything that is private

and in one way you can see that we can

use these base class access specifiers

the access specifier in derived class

but we can't make the access specifiers

more relaxed we can only make things

more constrained or more restricted for

example the m1 member variable was

public but now we have made it become

protected by using the protected base

access specifier here okay so now you

know that we can do public and protected

inheritance but it is also possible to

do private inheritance and you do that

by using a private base class access

specifier the moment you do this

anything that is public in the base

class is going to become private in the

derived class anything that is protected

in the base class is going to become

private in the derived class and

anything that is private is going to

stay private in the derived class and

again you see that this is going to

constrain thanks things that were public

are now private in derived and we can't

really do anything with them from any

other class that might derive from our

player class so this is the setup we

have okay to sum this up through the

base class access specifier we can

control how relaxed or constrained

is the access to base class members from

the derived class and this is really

important to understand if you want to

say as relaxed as they are in the base

class you can use public inheritance if

you want to constrain a little bit you

protected inheritance and things are

going to be inherited as protected

except for the private data in the base

class if you want things to be super

constrained you can use the private

inheritance that we just learned about

and everything in your derived class is

going to be private and you can use this

if it makes sense for the application

you are designing and you can use these

kinds of features if they make sense for

whatever application you are designing

with c plus plus one thing you should

know though is that regardless of the

base class access specifier we use

private members of the base class can

never be accessible from a derived class

so anything that is private is going to

stay private and you have no way to

relax things a little bit that's not

going to work you should really know

this now that you know these kinds of

inheritances we can do in ziplus plus

we're going to head over to the next

lecture and play with them a little more

in this lecture we're going to play with

the base class access specifiers we

learned about in the last lecture in

other words we're going to play with

public protected and private inheritance

in visual studio code so let's review a

little bit what we talked about in the

last lecture we say that we can have

public inheritance and the syntax to do

that is what you see here and at the

moment you do this what was public in

the basic class is going to be public in

the derived class what was protected is

going to stay protected what was private

is going to become private in the

derived class in other words public

inheritance is really not going to

change the accessibility of the member

variables we have in the base class

we're going to inherit the data as it

was with the same access level we had in

the base class this is a defining

feature of public inheritance in c plus

plus we can also do protected

inheritance and what this is going to do

is to make protected the highest access

level we can have in the derived class

so anything that was public in the base

class is going to become protected

anything that was protected is going to

stay protected because that's the

and anything that was private in the

base class is going to be private in the

derived class we say private in the

sense that it is going to be private to

the base class so you can't really use

m3 from the player class in this case if

you're trying to do that you're going to

get a compiler error okay we can also do

private inheritance and the syntax to do

that is what you see here and now

private is going to be the highest level

in the player class in terms of the

members that we get from the base class

so anything that was public is going to

become private anything that was

protected is going to become private

anything that was private to the base

class is going to stay private to the

base class this is what we mean here but

m1 and m2 just became public to the

player class if anybody else tries to

derive or inherit from a player these

things are not going to be accessible

and this is in some way the player class

being selfish it is saying i am going to

get everything i can from my parent

class or my base class but i am going to

make it all mine nobody else can take

this and this is the kind of setup we

with private inheritance okay so now

that we have this in mind we're going to

play with us in visual studio code we're

going to set up a bunch of classes we're

going to set up a personal class we're

going to be inheriting from we are going

to set up a nurse class which is going

to do protected inheritance and we're

going to set up an engineer class which

is going to do private inheritance and

we're going to really play with this and

see how this plays out in real c plus

plus code so let's do this here we are

in our working folder the current

project is base access specifier a demo

we're going to do a demo on this but

before we do that we're going to grab

our template files and put them in place

and we are going to open this little guy

in visual studio code by dragging and

dropping here this is going to give us a

good starting point we're going to have

our main cpp file we're going to clean

it up and we're going to set up our base

class which is going to be the person

class so let's put this in from scratch

we're going to add our files we're going

to say person page and we're going to

we are going to hop over in our header

file and put in our code nothing special

so far we have an include gourd we have

our person class it has a bunch of

member variables we have the full name

which is public we have the age which is

protected and we have the address which

is private to this class here this is

going to be our starting point

we also have a bunch of constructors we

have a default one we also have another

one which is going to take all the data

we can use the constructor person object

and here we are passing a cost string by

reference i think we can fix this and

pass a string view this is going to be

better let's say string view and we're

going to change the first parameter here

to be an std string view by value this

is going to be much better okay we have

our class we can hop over in the cpp

file and put in our implementation we

are going to change the constructor a

little bit and make sure we are taking

an std string view by value and if you

wanted to type all this code you can get

it from the resource section of this

lecture i am going to attach all the

source code and you can download and use

this however you want to really make

your learning experience as pleasant as

possible so we have our constructor here

it is going to forward the data into our

member variables the full name is going

to go into our full name member variable

we're going to grab the age and the

address and we're going to store all

this information we also have an output

stream operator which is going to be

printing all this information here it is

going to go through the getters because

we have a person object passed as a

parameter here and this is going to work

we can go in the main cpp file and

include our person class and create an

object of it we can do something like

person person one and we can pass the

data that our constructor expects we can

pass in the full name the age and the

address so let's do that we're going to

say the full name daniel gray why not

and the age is going to be 27 we can put

in whatever we want and we're going to

put in the address we're going to say

blue sky streak you can say two three

three for example and say the number of

the house to b56 why not this is a

possible address for a person so we can

say person one or we can use htdc out to

print this out because we have an output

stream operator for our person class we

can do this we're going to say person

one and we're going to put him out and

if we build and run this program we're

going to see that this is going to work

hopefully and we have a problem because

we don't have a semicolon at the end of

line 6 here let's fix that we're going

to run this task to build with gcc the

builder is going to be good we can bring

and we're going to use this to run our

program if we say rooster we're going to

see that we have the person printed down

the full name is daniel gray the age is

27 the address is blue sky street 233

and the number of the house is 56 so

this is a possible implementation for

the person class but we are really not

interested in setting up a prison class

and doing things with that we are

interested in inheriting from the person

class and learn about different kinds of

base class access specifiers we can do

so we're going to set up a player class

which is going to inherit publicly from

the person class let's do that we're

going to put in our player we're going

to put in the header file let's say

player not person and we're going to say

player.h we're going to put in a cpp

file we are going to hop over in the

header of player and put in our class

let's close the left sidebar here so

that you can really see everything we

we have the class player declared it is

going to do public inheritance from

and what this is going to do is that

anything that is public in person is

going to stay public in player anything

that is protected is going to stay

private is going to stay private so we

want to be able to access private data

from a person object for example we

the address member variable here because

it is private but we can use the full

let's make sure we have a cpp file and

so let's hop over to the cpp file and

put in a possible implementation we are

going to include the person and player

because we're going to be using these

and we are going to set up a constructor

which is not going to do anything for a

player we also have our output stream

operator which is going to print the

data it is going to be using the getters

we have in the base class and we have

because we are doing public inheritance

so they are going to be public and we

can call them from the outside like we

are doing here notice that this is an

outside player object and we are calling

our public members on it and this is

going to work we also have a destructor

and which is really not going to do

anything but we're going to keep it in

here because it's not going to hurt so

is to see if we can access thanks from

the base class the first thing we have

full name and i think we can actually

copy these blanks or we cannot just use

them m full name mh and m address we're

going to try and use them in the derived

class so let's try and say m full name

and change the full name for example to

daniel gray or jon snow and we're going

55 why not and we're going to try and

access the address let's see what we

called our address member variable it is

m address we can grab that and use that

in our class if we try to access that

we're going to get a compiler error

private to the base class you notice

that if we even try to put some junk

data we're going to have a squiggly line

because this is not accessible here and

visual studio code is going to say that

because it is private to the base class

so we can access m full name because it

was inherited as public so this is going

to be okay we can use age because it was

inherited as protected we can use it in

a derived class but we can't use the

address because it was inherited as

private and it is private to the base

class so this is not going to work even

if we try to call biola code we're going

to get a compiler error let's try to do

that so that you can really see for

yourself okay so we have a compiler

error and this was declared in the base

class as private this is what the

compiler error is saying so we shouldn't

really be doing this the derived class

modifying a private member of the base

class this is the message here so we're

going to comment this out and say that

this is going to give you a compiler

error but we are also going to create a

player object and try to access these

guys and see how accesses from the

outside so we're going to go in the main

cpp file and we're going to include

player dot h and we're going to create a

player object we can put in a separator

and say a bunch of dashes here this is

going to do i think this is going to

work and we're going to create a player

object we can say player and player and

not put any parenthesis here this is

going to call the default constructor

that we have in our player class and we

can try to use this but before we do

let's try and build and see that this is

going to build just fine we're going to

work with gcc let's do that we're going

to see that the world is good we can try

and access stuff from this player object

we can say player and say m full name

you see that this is accessible we can

to samwell jackson we can do that but if

we try and say player mh we're going to

see that this is not accessible here

because this was inherited as protected

if we go back to person we're going to

see that the age is protected so it will

be accessible in derived classes just

like we did in our play method of the

player class but we can't access the age

from the outside of a player object

because that's not going to be

accessible from the outside this is a

defining feature of the protected access

level so this is not going to work even

if we try to build we're going to get a

compiler error along the lines of this

is not accessible in this context and it

was declared in the base class so we

can't really access it from the outside

this is the compiler error here so we're

going to comment this out and say that

this is going to give you a compiler

error okay so i hope you know that you

can't even have a chance accessing a

private member of a base class from a

derived object in the main function like

we do here so if we try and do player

and say m address this is not going to

work okay so if we try to change this

for example to some junk data this is

not going to work we're going to get a

compiler error because this was declared

private in the base class and it is

private to the base class you can't

really access it from the outside you

can't even access it from a derived

class so let alone access this on the

outside in the main function so this is

not going to work it is going to give

you a compiler error but we're going to

weld and show you the compiler error

because we are learning here so we're

going to get a compiler error that says

m address is private within the context

where we are trying to use it so we

can't really use it from the outside

here again this is going to give us a

compiler error let's say that here and

this is really what i wanted you to

learn about public inheritance anything

that is public in the base class is

going to be public in the derived class

anything that is protected is going to

stay protected and what that means it

will be usable in the derived class but

you can't use that from the outside and

anything that is private in the base

class is going to stay private so you

can't use that from the derived class

and you can't even use that from the

outside like we are doing in the main

function here this is not going to work

okay so now that we have this in place

we're going to set up another class that

protected inheritance and that's going

to be our nurse class so we're going to

put this in let's put in a nurse header

file this is going to be nurse.h we're

also going to put in nurse.cpp okay so

we're going to head over in the header

file and put in the code for our nurse

class we're going to say cluster nurse

and say protected to mean that we want

to do protected inheritance and what

this is going to do anything that is

public in the base class is going to be

protected in the derived class which is

our nurse class anything that is

protected is going to stay protected

anything that is private is going to

to the base class this is what we mean

here okay now that we have this end we

can put in the implementation for our

nurse class and we're going to have a

constructor and we're going to have our

output stream operator and we're going

to have a destructor which is really not

going to do anything because we don't

have any dynamic memory allocation in

we are going to try and build this code

to see that it is going to work we have

a squiggly line in the main cpp file but

it was because of the line 15 here and

it has been commented down let's see if

we can build this program okay you see

that the world is going to be good and

thanks from our output stream operator

you see we have an earth operand we are

able to call this gateful name and get

because they are now protected in the

nurse class but we are able to call them

because this operator is a friend of our

nurse class here i want you to say this

some of you are going to ask

aren't we using an object and calling a

method using the dot operator this

qualifies as calling thanks from the

outside and yes that's true but this

method is really like a member function

in that it has access to private and

protected data from our nurse class and

the reason is it is a friend of the

nurse class here that's why we are able

something like this but what i really

want you to see now that that doubt is

cleared is the kind of access we have to

thanks from the base class we will still

be able to use m full name here because

it was inherited as protected so we can

use it from a derived class we can say m

full name jon snow this is going to work

inherited as protected now it is

protected in the eyes of the nurse class

this is what we mean here so this is

okay this is going to work we can get

the age we can use that and we can say

23 for example this is going to work

because this is protected but we can't

use the address if we do that we want to

be able to change it we will get a

this is private to the base class this

is the same thing we saw in the last

lecture this is going to give us a

compiler error if we try to build this

program let's try and build it to really

prove this the body is going to be good

without line 17 here but if we

uncommented and trying to build the

program let's do that we are going to

get a compiler error and the compiler

error is going to say let's go up and

see if we can get this message it's

m address is private within this context

where we are trying to use it and that's

line 17 of the nurse class if we go

there we're going to find the offending

line here so we're going to comment this

out and say that this is going to give

us a compiler error okay so you

shouldn't do this now that we know

things from the inside let's see how

on the outside we are going to hop over

to the main cpp file and include our

nurse class and we're going to create a

nurse object we can go down and say

stdcl and we're going to put in our

dashes and we're going to create a nurse

object i think we have a default

constructor for a nurse we're going to

say nurse 1 and we're going to basically

try and do the same things we did for

the player object from the outside if we

try to access the full name now it's not

going to be accessible because it was

with protected access level so if we do

nurse and say m full name you're going

to see that autocomplete is not here

this is a good sign that this is not

accessible from this place if we say

davy jones we're going to get a compiler

error and if we try to build we're going

to get a descriptive compiler error at

least i hope so let's build we're going

to see that with world with errors and

if we go up we're going to have our

error nurse was not declared in this

scope did you mean nurse one yes we met

nurse one sorry for that we're going to

build again thank you gcc for pointing

this out we are going to get another

kind of error and if we look at our

error here we're going to see that m

full name is inaccessible within this

context because it is a protected member

of the nurse class now it was inherited

as protected and we can't access it from

the outside we can access that from the

inside because it is protected but if we

try to access it from the outside we're

going to get a compiler error and this

of protected inheritance even things

that were public in the base class are

going to become protected in the derived

class so this is the message here and

this is going to give us a compiler

error okay so if we also try to access

h this is also going to give us a

compiler arrow let's try to put in an

edge here let's put in 51. you're going

to see that we're going to get the same

let's really try these things out and

learn about every possible way we can

if we look at the error we're going to

see that image is protected within this

context so we can't really access it so

this is the compiler error we get and i

hope you know that if you try and access

the address you're also going to get a

compiler error because that's private to

the base class so we can't even use that

from a derived class like nurse here

that's not going to work let's say that

here we have a compiler error and we're

going to set up another class which is

going to inherit privately and see how

that works out the class is going to be

engineer we're going to see that the

error here goes away so let's create our

engineer class we're going to put in a

header file that's going to be our

engineer.h we are also going to put in

cpp okay so we're going to hop over to

our header file and put in our engineer

class we're going to say engineer and

say that we want to inherit privately

from the person class this is the syntax

here and this is going to do private

inheritance and what this means is that

anything that is public is going to

become private to this class anything

that is protected in the base class is

going to become private to this class

and anything that was private in the

base class is going to stay private we

won't have access to that whatsoever in

the derived class directly we are going

to hop over to the cpp file and put in

our implementations we're going to have

a default constructor for engineer which

is not going to be taking any parameter

we're going to have our output stream

operator which is going to still work

because it is a friend of the engineer

class so all these things that were

inherited to be private are going to be

private to the engineer class and any

friend of the engineer class will have

access to that that's why we are able to

call get full name get age and get

address here and get these things to

work okay now that this is out of the

way we can try and access our thanks

we're going to try and do the same

things we did in our nurse header we're

going to copy the code because we are

trying to access the same member

variables and we're going to see how

this fairs in our engineer class this is

going to save us a few seconds

if we try to access the full name this

is going to work because it is private

to this class if we try to access the

edge this is going to work because all

to this class here but if we try to

access the address this is going to give

us a compiler error because address is

private to the base class if we go back

to person we're going to see that this

and if you try to inherit from this

class in any way you're not going to be

able to change this access level this

member variable is always going to stay

private to the base class and no derived

class will be able to modify or read

from this in any way so this is the

setup we have here if we try to build

we're going to get a compiler error

let's first take this out and show you

just fine without this line here

and i am going to build again and show

you that if we bring that in we're going

to get a compiler error so the build is

good we can go back in our engineer

class and bring in the offending line we

can uncomment this and if we want we're

going to get a compiler error let's make

sure you see the compiler error here so

the world was finished with errors and

if we go up we're going to see that we

have an error here and the error is

going to say m address is private within

this context and the context is what we

engineer class so we can go there and

find the offending line and we're going

to comment this out and this is going to

give us a compiler error now you know

this but this is how things are going to

work from the inside but we also need to

look at how things fare from the outside

let's go back in our main cpp file we

are going to include our engineer class

and we are going to create an engineer

object we can go down and say sddc out

and put in a bunch of dashes to separate

on thanks and we can create a

engineer object and that's going to be

engineer one and if we try to access the

full name that's not going to work

if we say engineer one and try to say m

full name and try to change the name in

olivier godson i am making this up i

don't know if this name exists but the

point is that this is not going to work

it is going to give you a compiler error

because m full name is now private to

the engineer class it was inherited to

be private to the engineer class and if

you try to do this you're going to get a

compiler error let's try and work with

gcc to really show you this and the

world is going to be finished with

errors and if we go up we're going to

full name is inaccessible from within

this context and the offending line is

at line 27 of the main cpp file if we go

there we're going to find our line and

we're going to say that this is going to

give us a compiler error so let's say

that and we can't even access the age

and the address member variables the age

is also going to be private to engineer

but the address is private to the base

so that's not going to work either so we

can't really access that from the

outside because it is now private to the

engineer class so let's go down and

really show you that we're going to go

down and say engineer one and say mh if

we try to do that that's not going to

work that's going to give us a compiler

error and if we try to build we're going

to get a compiler error along the same

lines as what we just got here

the book is going to finish with errors

and if we look at our error we're going

to see that mh is protected within this

context so we can't use it at line 28 of

the main cpp file this is going to give

us a compiler error let's do that we're

going to say that here and if we try and

access the m address member variable

that's not also going to work because

this is even more restricted for access

it is private to the base class so we

can't access it from a derived class

directly we can't even access that from

the outside so you should really know

this so if we put in some junk data here

and try to build this is going to give

us a compiler error that says that this

is not accessible from the main cpp file

like we are trying to do on line 29 here

so we're going to get an error and the

error is going to say m address is

private within this context and the

offending line is at 29 of the main cpp

file we're going to take this out and

we're going to say that this is going to

give us a compiler error this is really

all i wanted you to see in this lecture

and before we wrap this up let's try and

build again and make the error go away

because i don't like to leave you with

code that has compiler errors and the

book is good and this is really all i

wanted you to see in this lecture that

you can do all kinds of inheritances in

your c plus plus code you can do public

inheritance you can do protected

inheritance you can do private

inheritance and we had a chance to look

at all these scenarios in this lecture

here the message is the same as we saw

in the last lecture if you do public

inheritance anything that is public in

the base class is going to stay public

in the derived class anything that is

protected is going to stay protected

anything that is private is going to

stay private and this is really

misleading in a way the private data

from the base class is not going to be

private to the derived class it's going

to stay private to the base class so if

you try to use this in any way from the

derived class you're going to get

compiler errors because you can't access

that even if it is part of you player

has a person part of it but it can't

access private members from the base

class you should really know this we

have seen that we can also do protected

inheritance and that's going to

the highest level of access to be

protected so anything that is public is

going to be stripped down to protected

access anything that is protected is

going to stay protected anything that is

private is going to be private to the

base class you should really make this

super clear we can also do private

inheritance as we saw and this is going

to strip down the highest level access

to be private so anything that is public

is going to be constrained to be private

anything that is protected is going to

be inherited as protected to the player

class but anything that was private in

the base class is going to stay private

to the base class even the player class

won't have access to this member

directly if we really need access to

private data from the base class we

might go through public getters or

anything we get from the base class but

we can't access m3 directly and use it

from the derived class that's going to

give us a compiler error this is really

all i wanted you to see in this lecture

and i hope you find this interesting we

are going to stop here in this lecture

in the next one we're going to try and

zoom in on private inheritance and show

you some things you really need to be

so go ahead and finish up here and meet

in this lecture we're going to zoom in

on private inheritance and we're going

to see that the class that does a

private inheritance is really selfish

here is a simple structure we will be

using in this lecture here we will set

up a person class which is going to act

as our base class we are going to

inherit from this class privately and

and what this is going to do it's going

to take everything from the class person

and make it private to the engineer

class so the m1 member variable which

was public in the base class is going to

be private to the engineer class this is

what we have here the m2 member variable

which was protected is going to become a

private in engineer that's what we have

and the m3 member variable which was

private to person class is going to stay

private to person in the eyes of

engineer this is the situation we have

here so the problem is going to really

show up when somebody else tries to

inherit from engineer because m1 and m2

are now private to engineer they will be

inherited but still inaccessible to the

civil engineer class here m1 and m2 will

be private to the engineer class but m3

will be private to the base class which

is person so hopefully you can see the

message that if a member variable is

it can't be inherited in any way it

doesn't matter which kind of inheritance

you do so starting from engineer which

has made m1 and m2 private to itself

it's no longer possible to forward these

guys down in the inheritance hierarchy

another way to look at this is to see

that the engineer class is really

selfish it is saying i am going to take

everything i can get from my parent

inheriting privately but nobody else

will be able to take things from me

because i'm going to make them private

to myself so even if civil engineer is

that's not going to give him any access

to these member variables which are now

private to the engineer class hopefully

you can really see this and private

inheritance is going to really constrain

what you can forward down to other

classes that are going to be inheriting

from you this is the message i am trying

to convey here okay so here is the same

example in code we have our person class

it's going to have our member variables

we're going to have the full name the

age and the address they are going to

have public protected and private access

we are going to inherit from person and

create our engineer class we are going

to privately inherit from person and

this is going to take everything we get

from person and make it private to the

engineer class and one exception is

what was already private to the base

class which is our person class here

this is going to still stay private to

the person class regardless of what kind

of inheritance you do from person but

any other thing if we have any member

variable which are public or protected

or even if we have some member functions

which are public or protected everything

is going to be private to the engineer

class because we have done private

inheritance here so if we inherit from

engineer and do any kind of inheritance

we are going to do the most relaxed kind

of inheritance which is going to keep

the kind of access we had in the base

class but this is not going to improve

anything everything is going to stay

private to the engineer class and the

civil engineer is really not going to

have any access to any member variable

or member function that is inherited

from the engineer class and we are going

to see this in a minute when we hit

so again if a class is doing private

inheritance it's really another way to

say this class is selfish it's going to

take everything it can from the parent

class but it's not going to forward

nothing to downstream inheritance

classes and this is the setup i really

want you to understand here and only do

private inheritance when you want this

kind of behavior now that you know this

we're going to head over to visual

studio code and play with us a little

here we are in our working folder the

current project is closing in on private

inheritance we're going to zoom in on

this and really understand the effects

of doing private inheritance we're going

to grab the code from the previous

lecture and we're going to grab the

the person class these are going to be

our starting point here make sure you

grab the dot vs code folder if you are

using vs code with this course that's

going to give you the basic settings we

need to do our c plus plus program i am

going to copy these guys down and put

these in our current project and again

make sure you have the main cpp file the

person class and the engineer class and

these are going to be our starting point

so we're going to open this little guy

in visual studio code by dragging and

dropping here we're going to look at our

main cpp program we are not going to

include nurse because we don't have this

and we can really take out everything we

have in the main function we're going to

be adding our own thing here we also

don't need the player class here we're

just going to be using person and

engineer let's look at the person class

it is going to have the member variables

we are going to have a public member

variable the full name a protected

member variable mh and a private member

variable m address here we are going to

create an engineer class which is going

to privately inherit from person

so it is going to make everything

private to itself the engineer class is

going to have a person part in at but

the member variables we get from the

person class are going to be stripped

down to private access level except for

the member variables which are already

private in the base class and that

happens to be the address so it doesn't

matter which kind of inheritance you do

the m address member variable is going

to still be not accessible to

inheritance classes this is going to

still be private to the base class which

is the person class here so the

full name is going to be stripped down

to private access level in engineer the

edge is also going to be stripped down

to private access and these are going to

be private now to the engineer class and

any class that tries to inherit from

engineer is not going to have access to

these guys so if we do any kind of

inheritance from engineer we want to

have access to full name we want to have

access to mh because these are going to

be private to this class here this is

the setup we want to understand in this

lecture so what we're going to do we're

going to set up a new class which is

going to inherit from our engineer class

and it is going to do public inheritance

and we're going to see how this works

we're going to create a civil engineer

class which is going to inherit from

engineer so let's do this we're going to

create a header file for our civil

engineer class and we're going to create

we are going to head over in our header

file and put in the class it's not going

to be anything sophisticated we're just

going to have in our include guard we're

going to create a civil engineer class

which is going to publicly inherit from

engineer but remember everything was

made private to the engineer class so

even if we're doing public inheritance

the full name member variable is going

to be private to engineer the age is

going to be private to engineer and

engineer won't have any access to these

guys but before we really play with that

we're going to put in our implementation

so let's put in the code here we're

going to put in the implementation and

we're going to have our constructor in

place but notice what happens on our

output stream operator the output stream

operator is a friend of the civil

engineer class so it should have access

to anything we have in our civil

engineer class but notice what is

the get full name method is not working

private to the upstream class which

our engineer class and we can't really

access them even if we know that they

are really part of the interface of the

person class we have them as public

members of the person class but when the

engineer class did private inheritance

it made everything that is not private

to person private to itself so these

gators are going to be private to

engineer when the engineer does private

inheritance the member variables which

are public and protected all these

things are going to be stripped down to

private access level so they are going

to be private to engineer and any kind

of inheritance you're going to do is not

going to change that they are going to

be inherited as private to the engineer

class that's why we can't even call them

from a function which is a friend of our

civil engineer class and we know that if

you mark something as a friend it's

really going to have access to anything

you have including private members but

we can't call any of the members from

the engineer class because everything is

now private to the engineer class this

is what i want you to see if you do

private inheritance this is going to

anything from the upstream class and

make that private to the class that is

doing private inheritance this is the

message here and again if you go in any

method of the civil engineer class and

try to do any kind of access for example

method is not going to board well we're

going to see that this is inaccessible

here if we try to access m full name

for example change this to be something

gray this is not going to work if you

and change it to 45 for example this is

not going to work we already know that

the address is private to person so we

shouldn't really try to access it

because it is inaccessible regardless of

any kind of inheritance you do but the

members that were public from person

can't be accessed from any class that is

inheriting from person even if we know

that these things are public or

protected in the person class

and this is really what i want you to

see if we try and build our program

we're going to get a bunch of compiler

errors saying that we can't access these

from our civil engineer class we are

going to use the gcc compiler here

because it is our favorite and we're

going to see our compiler errors here

okay so we're going to get a bunch of

errors let's go up and see all of them

we're going to get an error saying that

getfullname is inaccessible within the

context of the c4 engineer header class

at line 13 we are calling this method

that's not going to work we have another

error here saying that the getfullname

method is not accessible from line 13 of

okay it is really the same error but if

we go down we see that we get a bunch of

other errors we have m full name which

is not accessible we have m edge which

is not accessible we can't really do

these kinds of things from the civil

engineer class because all these are

going to become private to the upstream

class that did private inheritance so

show you that even if we can't access

these guys they are still part of our

civil engineer class and we're going to

use a debugger to do that i am going to

take out these things or i can comment

them out and say that they are going to

give you compiler errors i think this is

going to be more descriptive so let's

and access to the edge is also going to

give you a compiler error and we're

going to go down and show you that we're

also going to have the same problem in

our output stream operator so if you

really want your output stream operator

to work here what you can do is put some

in the engineer class and make it give

you access to the members that were

eclipsed to private access in this class

here for example you can return the full

name you see that we can access that

here you can return the age but you

still don't have access to the m address

member variable because this is private

to the person class but i really don't

even want to do this because doing this

is sign of bad design in the first place

so if you need to do those kinds of

getters and forward them down to

inheritance classes why not change the

design in the first place and not to do

private inheritance here for example if

you change this inheritance to protected

or public these members are going to be

directly automatically forwarded down to

any inheritance class so just know that

you can put in public getters that are

going to give access to the full name

and age but you still want to be able to

from the inheritance class because this

is the design you achieve by marking

something as private in the base class

if you want the address to be forwarded

down you might change the access level

we have here and maybe make it protected

or public so this is the ideas i really

want you to grasp i am going to comment

out the offending code here because i

want you to be able to build this

program and see that even if we can't

access this get full name and get

address members from inheriting classes

they are still part of our interface we

just can't have access to them because

of the choices we have made in upstream

classes so what i am going to do i am

going to go in my main cpp file and i am

going to create an engineer object

i will also include civil engineer here

let's do that and i am going to create

an engineer object and i am going to

create a civil engineer object

and i am going to just say done here and

i am going to put the break point on

line 12. we are going to use a debugger

that engineer objects and the civil

still have a person part of them we just

can't access the interface that was

eclipsed by the engineer class so we are

going to hit the run tab here

start our debugging session by clicking

we are going to build our program and if

the build is good we're going to plug

the binary that was generated into our

debugger and we are going to hit our

break point in a minute once we hit our

break point we are going to look at the

local variables we have in the main

function we're going to see them on the

left here if we expand we're going to

see that we have an engineer one object

and we have a civil engineer one object

if we look at our engineer we're going

to see that we have a person part of

this which is our base class and if we

look at civil engineer it's also going

to have a base of engineer so any civil

engineer is also going to be an engineer

but the engineer part of the civil

engineer also has a person part of that

you should really see this information

and the main message i want to convey

here is that all these objects have a

person part of them we just can't access

that part in objects of our inheritance

classes because of the design decisions

we have made let's close this off now

that you have seen this and again

inheritance hierarchy the base class is

and it's going to have these member

but if we do private inheritance from

the person class anything that is not

public is going to be eclipsed down to

private level access so any other class

that is going to inherit from our

engineer class now is not going to have

direct access to these members because

they are going to become private to this

class here and that's the experience we

use any of this methods and members we

this is not going to work because they

private to the engineer class this is

the message here so the get full name

methods are not going to work if we try

to use the contract count member which

comes from the engineer class that's not

also going to work if we look in our

header and try to use any of these

members we're going to get compiler

errors because all these guys are now

private to the engineer class this is

really all i wanted to share in this

lecture let's head over to the cpp file

and comment this out again because i

don't want to leave you with these

compiler errors i hope you found this

we are going to stop here in this one in

the next one we're going to see that we

can actually resurrect some members back

if they were eclipsed by the kind of

inheritance we did from an upstream

go ahead and finish up here and meet me

in this lecture we're going to explore

how we can resurrect members back in

scope so what do we mean here suppose we

have our trusty inheritance tree here we

have a base class person the engineer

class is going to do private inheritance

and it's going to really be selfish and

i am going to take everything i can from

the upstream person class but i am going

to make everything my own and nobody

inherited from me will have access to

these guys for example m1 and m2 are

going to be private to the engineer

starting here when the engineer class

does private inheritance so any other

class for example civil engineer which

the engineer class in any way won't have

to the m1 and m2 member variables so

suppose for some reason that we have

this kind of setup here but again we

want some members to be accessible to

suppose for example we want the m1

member variable to still be accessible

to downstream classes while we have done

private inheritance c plus plus is

really weird in a way it is going to

work hard to really prevent you to do

thanks and that gives you a back door

allow the same thing you were trying to

avoid in the same place it is the same

kind of logic we have here it allows you

to use private inheritance to prevent

downstream classes to access to anything

you get from upstream classes but then

again it allows you to change that and

relax the access to downstream classes

for example we can change the access of

m1 and m2 make it more relaxed make it

public or protected if we wanted that so

let's take a look at some code because i

know that these things can really be

confusing okay we are going to start

from a person class which is going to

have a bunch of member variables we will

also have a bunch of getters that are

going to return all these member

variables and we are going to do private

inheritance from person in an engineer

class this is going to strip down access

to the members we get from person

private level access for example they

get full name member function the gate

age the gate address member functions

engineer class now but for some reason

you might want to resurrect them

to a more relaxed access level and you

do that using the using keyword so the

first thing you need to do is to choose

the section in which you're going to be

putting these using statements for

example because we put them in a

all these guys are going to be

resurrected with a nexus level of

protected if we put them in a public

section they are going to be resurrected

with a public access level and they are

going to be accessible from inheriting

classes one thing you should know is

something that is already private to an

upstream class for example we know that

our m address member variable was

private to the person class so we can't

really resurrect that in an inheritance

class if we do that we're going to get a

compiler error and hopefully this is

going to drive the point home that

private inheritance is really really

serious and that it's going to strip

down access to private level access in

an inheritance class and any downstream

inheritance class will never be able to

resurrect those member variables to a

more relaxed access level so because

everything here is inherited as private

by default any downstream inheriting

class will never be able to resurrect

these guys for example to public or

protected scope this is the message here

and you can use this kind of design if

you want that but personally i don't

like to do this because it's going to

hard to read and understand if you want

these guys to be public or protected why

not make them public or protected in the

first place and really not use private

inheritance that's going to be much more

direct to see and understand and your

code is going to be easier to work with

for you in the future or for some other

developers that will get to work on your

code in the future so this is the

message here you can use this feature to

to a relaxed access level and now that

you have an idea about this we're going

to head over to visual studio code and

here we are in our working folder the

current project is resurrecting members

back in context we are going to

completely reuse the code from the last

lecture because it's going to give us a

good starting point we can copy

everything except for the binary here we

don't need that in our current project

we're going to put in our starter code

and we're going to open this little guy

in visual studio code so we're going to

have our code we're going to have our

main function and we're going to have

all these objects created here i'm

really not sure if we're going to need

this yet so let's take this out and

we're going to look at our personal

class it is going to have our members

here and we are going to have a bunch of

getters which are going to be returning

these member variables and we have a

constructor here which is really going

to build a person object nothing

complicated here we have an engineer

class which is going to privately

inherit from person and we know that

this is going to eclipse everything that

is not private in the person class to

private level access so everything is

going to be private to the engineer

class now but sometimes we don't want to

do that for example if we go down in our

the get full name and the getage methods

are going to be private to the app

stream engineer class and that's going

to break the code for our output stream

operator and it's not going to work

because we want to have access to get

full name and get age and that's also

going to kill access we had on the get

address method which would give us

access to the address member that we

have in our person class let's make sure

i am confused here we have a lot of

it is down here so we have the get

address method which is going to return

the address we want to have access to

that in our civil engineer class to be

able to print all this information if we

also want to print the contract count we

can go in our engineer class and put in

a method which is going to return that

and say get contract count and this is

going to be a const member function

because it's not going to be modifying

our object we're just going to return a

value we're going to return the contract

count and we can go in our civil

engineer implementation file and change

get contract account we can do that okay

we have this method now we want this to

work this is going to work because we

are doing public inheritance from the

civil engineer class but we want this to

work we want to get full name get age

and get address to work here and we can

use the using feature to resurrect these

members to an access level which will

allow our civil engineer class to pick

them up so we can go in our engineer

class and set up for example a public or

protected scope we're going to use

protected because we want these to only

inherited classes for example so we're

going to say protected and we're going

to say using this is the syntax we're

going to say person and we're going to

say get full name we're going to say

using person get age going to choose

this and we are going to say using

person and say get address i think we

have that method here the moment we do

this we're going to go in our civil

engineer class you're going to see that

it is going to work now because what we

just did is resurrect these members to

have protected access level in the

engineer class so the inheritance

classes are going to look at this and

see that they have a protected access

level in the engineer class and they are

going to be forwarded down to any

inheritance class we could also change

this to public this is also going to

work they are going to be inherited as

public and hopefully you can see that

any member that you resurrect it's going

to take the excess level of the section

where you resurrect it if we resurrect

them in a public scope they are going to

be resurrected with a public access

level if we resurrect them in a

protected scope they are going to be

protected access level and this is the

message here now if you happen to have a

bunch of overloads in an upstream class

for example suppose we have a bunch of

functions in the person class we can go

in and put in let's do that we can go

double or ent let's say and that's going

to be much simpler we can say add and

a and say ent b and say ent c we're

three things that we are adding this is

going to be a const member function it's

not going to be modifying our members in

any way so we're going to return

plus c this is something we can return

and we're going to do an overload of the

the addition of two parameters so we're

going to only have a and b and i think

we can use a and b in the first

overload here that's going to be much

easier to follow so we have one that

and we have another one which is going

to add three parameters if we

privately inherit from person these guys

are going to be stripped down to private

level access in the engineer class and

they want to be accessible from in any

other downstream class so for example if

we head over in our civil engineer class

10 to two for example we're going to get

a compiler error because we don't have

access to this but we can also resurrect

these ad members in our engineer class

so let's go there and we're going to set

section in this class here and we're

going to say using person add this is

going to resurrect all the overloads

that we have in our upstream class and

this is going to be the case because we

resurrect only based on the name of the

the same name for a member function can

be shared by many overloads so if we do

this kind of resurrecting we are doing

member function from person we are going

to get all the overloads if we go in

civil engineer we will be able to use

the member function taking two

parameters we will also be able to use

the one that takes three parameters they

are all going to be resurrected here

this is the message i want to convey if

we do this you're going to see that this

is going to work and our code is going

to just world fine let's build and see

if the build is good actually we're

going to pass this through gcc the world

is going to be good so everything is

working just fine and the message i

really wanted to convey is that it is

possible to resurrect members

in a more resurrected access level if

you are inheriting using a really

constrained base class access specifier

for example we are inheriting using a

access specifier this is going to

eclipse everything we get from the

upstream class to private level but if

you think that's too much and you have a

few members that you would like to put

in a more relaxed access level you can

use this resurrecting feature and it is

going to make things accessible in

downstream classes if that's what you

want in your program and again i hope

this drives the point to home that

ziploc plus is going to sometimes work

really hard to prevent you from doing

one thing and then again give you a back

door you can go through to do that same

thing this is the same thing here we are

doing private inheritance but we aren't

relax the effects of private inheritance

by bringing things in a more relaxed

access level and you can use this if it

makes sense for your code again i don't

like this personally because it's going

to make code confusing if other

developers see that you are doing

private inheritance they are going to

expect everything from the app stream

to the class that is doing private

inheritance and if they see that they

can use this thanks that should be

private by default and downstream

classes this is really going to confuse

them and it is going to cost them more

minutes to look at your code to really

understand what is going on so if you

really want this dance to be accessible

in downstream classes why not do public

or protected inheritance in the first

place this is my argument here but it is

going to be your choice my job here is

to make you aware of the possibilities

that you have in the ziploc plus

programming language okay the last thing

i want you to see in this lecture is

that if there is something that was

already private in an app stream class

you can't resurrect that if you try to

do that you're going to get a compiler

error this is also going to drive the

point home that you can also resurrect

member variables so far what we have

only resurrected was all member

functions and we can also resurrect

member variables so we're going to try

and resurrect the m address member in

the engineer class and let's see how

this works out so let's go in our

engineer class we can go in our

protected section we can do this really

in any kind of section we're going to

say using and we're going to say person

and we're going to say m address you see

that this is not going to be

available in autocomplete this is going

to be a sign that this is going to give

us a compiler error and if we're trying

to do that we're going to see that we're

going to get a compiler error the

message here is that if something is

already private in a nap stream class

you can't resurrect it it is it claps

and hopefully this drives the point home

again that private inheritance is really

serious for example in our civil

engineer class we can't resurrect

something that was already eclipsed to

private level access by the engineer

class let's go in our personal class and

see if we have any other member function

play with we're going to put in a member

function that says do something we're

do something and it's going to be

constant it's just going to say hello we

can do something like this we are

and this method is going to be eclipsed

down to private level access because we

are doing private inheritance from

person let's go back in our engineer and

comment this out because it is going to

give you a compiler error if you build

a weird compiler error i think i should

really show you this because we are

learning here so we're going to try and

build our program anyway we're going to

and we're going to see the kind of

and we are going to see that there's no

member std this is a problem we just

introduced in our class here i think to

solve this problem we can just put our

definition in the cpp file we can do

that we're going to grab this and we're

going to put the definition in

person.cpp because we have io stream

included in there this is going to make

our code work much better let's do this

we're going to say void and say person

and we're going to say sddc out hello

this is going to fix our problem here

and the only problem we will have will

where we are trying to access things

that are now private to the base class

why do we have this weekly line here

and try to build really make sure that

and it was a visual studio code messing

with us so we're going to bring this in

and the world and we're going to see the

kind of compiler error we get here

this is what i am trying to make you see

you see the bullet is finished with

errors if we go back we're going to see

that string person m address is private

within this context we can't really

resurrect it if we do this we're going

to get this compiler error here this is

the message you shouldn't really try to

something that is already private to an

upstream class and that's what we are

doing here we are trying to resurrect a

member which is private to person and

this is not allowed in c plus plus if we

do that we're going to get a compiler

okay so but what i want you to see here

is that a public member which was in the

base class was also eclipsed down to

private level access in engineer so if

the do something method in our civil

engineer class we're going to get a

compiler error so let's try and do that

we're going to put a public section why

and we're going to go down and say using

and it say do something we have this

method here but if we do this we're

going to get a compiler error because

this method is now private to the

engineer class and why is it private to

engineer well engineer is doing private

inheritance that's going to accept

everything to private level access by

default so this member is private to

engineer we are inheriting from engineer

and this is going to be already private

to engineer and we can't resurrect this

back so if you eclipse something using

private inheritance you want to be able

to resurrect that to a more relaxed

access level in downstream classes this

is the message i am trying to convey

here so this is also going to give us a

and if we try to build our program we're

going to see that let's pass this

through gcc we are going to see that's

the world finished with errors and if we

go back we are going to get some kind of

error that says that do something is

private to some class it is inaccessible

within this context this is the message

we get from this particular compiler we

are using but the bottom line is that

you shouldn't really try to resurrect

something that is already private to an

upstream class and this is what we are

doing here you shouldn't really do that

let's comment this out and get a code to

so the web is good and we are all fine

here this is really all i had to share

in this lecture i hope you found it

interesting we are going to stop here in

this one the next one we're going to

explore how constructors work with

go ahead and finish up here and meet me

in this lecture we're going to zoom in

at how derived objects are built and

we're going to zoom in on the

constructors that we have been ignoring

on purpose so far so here we have the

inheritance hierarchy we will be using

it is what we are familiar with at this

point we have a personal class which is

going to be our base class we have an

engineer class which is now going to be

doing public inheritance because we have

seen enough of private inheritance our

engineer class is now going to be nice

i am inheriting from person but i also

want my downstream classes to have

access to the cool stuff i am getting

our engineer class is behaving now we

are also going to have a civil engineer

class which is going to publicly inherit

from engineer but what we want to focus

on here is what we get from base classes

so the engineer class is going to have a

person part of that but it is also going

to build on top of that and add an

engineer level and customize what kind

of person it is so if we inherit from

engineer and that weld our civil

engineer class the first link to be

built by c plus plus is the person part

of this it is going to build an engineer

level of this and then we are going to

to add the customizations that the civil

and a c plus plus is going to do this

using constructors by default we are

going to be using default constructors

if we don't specify a way for the

basical structure to be called c plus

plus is going to call the default

constructor to build your base objects

so if we set up something like this and

try to run a program we're going to get

output like this we're going to see that

the person default constructor is going

to be called first and notice that we

are building a civil engineer object so

the default constructor from the most

base class is going to be called then

we're going to be building an engineer

layer on top of the person stuff that we

get then we're going to build a civil

engineer layer on top of the engineer

stuff that we have already got and the

compiler is going to do this using the

default constructors by default so we're

going to call the default constructor

for person first we're going to call the

default constructor for engineer and

then we're going to call the default

constructor for civil engineer to

complete the construction of our object

the object will be complete at this

point and we will be able to use it

later on in our program here and

hopefully this is going to drive the

that you should really really always

provide to the photoconstructors for

your classes because the compiler may

call these default constructors in

unexpected ways especially if your class

is part of an inheritance hierarchy for

example if somebody tries to build the

civil engineer object and you don't have

a default constructor for a person the

compiler is going to try and code that

and it's not going to find that and it

is going to throw a compiler error as we

are about to see in a minute okay so the

message really in this lecture is that

the most base part of your class is

going to be bolt so for example for our

civil engineer class we're going to

build the prison port first then we're

going to build the engineer park and

then we're going to build the civil

engineer part of that and then we're

going to finish the construction of our

object this is the message here now that

you notice we're going to head over to

visual studio code and play with this a

here we are in our working folder the

current project is default argument

constructor with inheritance we are

going to reuse the code from the last

lecture because that's going to give us

the classes that we need to play

with what we want to do in this lecture

and that's playing with default

constructors let's put in our starter

code and we're going to open this little

guy in visual studio code let's do this

so we're going to have our classes we're

going to have the main function which we

and we are going to look at the person

class and make sure we have a default

constructor we are not going to default

it this time because we want to have a

body we can put our output statements in

so in this case we're going to go in the

cpp file and put in a default

constructor we're going to say person

and person and person here and this is

going to be our constructor we're going

to say stdcl defaults constructor for

okay so the personal class is done we

have a default constructor that works as

we want and we're going to go to our

engineer class and we're going to change

it to do public inheritance i think this

is going to be much easier to deal with

and we're going to remove all these

resurrection we were doing here from the

last lecture because this is no longer

and what we really want is to look at

our default constructor which is really

in here already let's look at the

implementation all we really need to do

is put in sddc out and say default

and we're going to hop over to the civil

engineer class and see if we have a

default constructor and we do have it

and we're going to go to the cpp file

so this is going to basically do what we

want and what we really want to see

is how or the order in which our

constructors are going to be called if

we build a civil engineer object as we

have seen here the person part is going

to be built first so this is going to

call the constructor from person and

because we are not doing any kind of

customization on which constructor is

going to be called the compiler is going

to call the default constructor by

default so we're going to build the

person port first and we're going to see

the default constructor for a person

called after that we're going to build

and this is going to call the default

constructor for engineer and after that

we're going to weld the civil engineer

part of us and that's going to call the

civil engineer default constructor this

if we build a civil engineer object so

we are going to hop over in the main cpp

file and actually build the civil

engineer object we're going to say civil

engineer and we're going to say ce1 we

can do that and we're going to see what

happens let's try and build this program

we're going to build that with gcc the

book is going to be good we could run it

let's bring up a powershell window we

we want to bring up a powershell window

and you're going to see that default

constructor for a person called the

first constructor for engineer called

engineer called this is what we want to

see and hopefully this proves that the

compiler is really going to build a

civil engineer object in parts the

compiler is going to see that it is a

derived object and it's going to see all

the classes that this is deriving from

so it is going to build the most base

part first after that it is going to

build other layers until it reaches the

level where we are at at this civil

engineer objects again if we put another

statement out here i'm going to say

and we're going to say sdd-endl

and i am doing this so that i just have

a point where i can put my breakpoint

some ides are not going to like it if

you put a breakpoint at an empty line so

that's why i am doing it here and i am

going to try and debug and really show

you that we have an engineer and a

person part in us i have shown you this

before but it doesn't really hurt to

because debugging is really cool it's

going to give you more information than

we're going to hit our break point here

locals we're going to have our civil

engineer object which is in scope now

and you see that we have an engineer

part of us and the engineer has a person

partner so what the compiler is really

going to do when it is building a civil

engineer object it is going to build the

most based part of us so it is going to

build a personal part after that it is

going to build an engineer layer on top

of that and then it is going to world

the servo engineer layer and that's what

we see in our output when we get to run

our program here if we go back we're

going to see that we still have our

let's bring up a terminal window we can

use to run this we're going to run

rooster and we're going to see the order

in which our constructors are called

this is really cool now that we have

just debugged this program you can take

out this hello line because it's really

useless and this is really what i wanted

you to see constructors are going to be

called in your inheritance hierarchy

going down to the most specialized one

so we're going to call the most best

constructor which is person and we're

going to keep going until we reach the

most specialized which is a civil

engineer here to build our object and

our object is really going to be build

up in layers this is the message i am

trying to convey here this is really all

i had to share in this lecture i hope

you found it interesting we are going to

stop here in this one the next one we're

going to see that we can actually

actively call a base class constructor

from our derived class and that's going

to add much more flexibility in how our

objects are built we are not going to

call the default constructor we're going

to be calling our own constructors and

have much more control on how our

derived objects are set up in the world

go ahead and finish up here and meet me

in this lecture we're going to see a way

we can instruct for custom constructors

when our derived objects are being built

in the last lecture we saw a figure like

this we had an inheritance hierarchy

that went from person to engineer and to

civil engineer and we saw that if we set

up a civil engineer object a personal

part is going to be built first an

engineer part is going to be built on

top of that and the civil engineer part

built and then we're going to have the

construction complete for our civil

engineer object but in the last lecture

we saw that this was calling the default

constructors and sometimes you don't

want this you want your objects built in

a specific way for example through a

bunch of parameters that you pass to

your constructor what if you want this

kind of setup this is what we are going

to learn about in this lecture and what

we want to end up with is something like

this we will be able to build a person

object by passing in a bunch of

the full name we can pass in the age i

think this is the age we can pass in an

address we can build an engineer object

by passing in this kind of information

we can pass in the name the age and the

address but we can also pass in the

contract count i think this is the new

member variable we had in our engineer

class but we're not going to stop there

we can also build the civil engineer

object and we can pass in the

information again a civil engineer is

also a person so we're going to be

passing the information that is going to

initialize the person part and that

happens to be the name the age and the

address but a civil engineer is also an

engineer so we're going to pass

information that portrays to the level

of an engineer and that's going to be

the contract count and we're going to

pass the information to initialize the

civil engineer part of this object and

that's going to be the road strength

and hopefully from this you can see that

to forward all this information to the

constructor where this information is

needed for example if we are building a

civil engineer object we want to forward

the name the age and the address to the

person part of us so we need to parse

this to our personal constructor in a

way we need to pass the 31 here to our

engineer constructor because this

information is going to be stored at our

engineer level and we need to store the

road strength information into the civil

engineer part of us because that's where

this member variable is declared

hopefully you can see the need to call

custom constructors which are not to

default these custom constructors are

going to allow us to forward information

when building our objects like we are

doing here in the main function so let's

see how we can do this some of you might

think uh-huh if i am building an

engineer object i can just grab the

information and pass that to my base

class and that is simple right so we can

grab all this information we can grab

the full name the age and the address

and pass that to our base class using

the syntaxes we have here if we are

doing public inheritance we're going to

have access to these guys anyway so we

can say full name equals full name mag

equals age and say m address equals

for the address is actually private to

the person class and we can't do

something like this if we try to access

the address member variable from the

base class and modify it we're going to

get a compiler error that says that the

address is actually private to the base

person class we can't do this so this is

not going to work okay some of you might

think uh-huh what if i try to use an

initializer list and do something like

this so i can say m full name and pass

in my information i can say mh and put

in my information i can say m address

and put in my information and then

the member variable that actually

belongs to the engineer class that we

are trying to build an object for here

and hopefully this is going to work

except the compiler is not also going to

accept this the reason is with

initializer lists you can't initialize a

member variable that doesn't belong to

the class that you are trying to build

an object for so for example here we are

trying to initialize m full name mh and

m address but these member variables

don't belong to the engineer class that

we are trying to build an object for so

we're going to get a compiler error here

this is not going to work it is not

to build or set up this member variables

so this is not going to work okay so

how are we supposed to forward

information from derived classes to base

not to worry here we can still use

initializer lists but we are going to

use constructors whose job is going to

be to initialize these member variables

so if we are building an engineer object

and we have information that really

belongs to the person part of us we're

going to call the person constructor to

actually use this information to build

the personal part of us and we're going

to be calling the person constructor in

our initializer list here and after we

do that we're going to initialize a

member variable that actually belongs to

us in our initializer list this is going

to forward information from derived

classes in this case the engineer is the

derived class and the information is

going to be forwarded to the person

constructor which is our base class this

okay now that you know this we're going

to head over to visual studio code and

here we are in our working folder the

current project is constructors with

inheritance we are going to grab the

code from the last lecture because

that's going to be our starting point

we are going to open this little guy in

visual studio code by dragging and

dropping here and this is going to give

us our starter code we're going to have

a person class an engineer class and a

civil engineer class and this is

basically going to set up the hierarchy

we have here and what we want to achieve

is to be able to call our own custom

when we build our object in layers

information is going to be coming from a

and we are going to initialize the

person part of us with relevant

we're going to initialize the engineer

part of us with relevant information and

we're going to initialize the civil

engineer part of us with relevant

information this is what we want to

achieve okay for that to work we need to

not call default constructors we want to

call actual constructors that are going

to grab the information and forward that

in our member variables for example in

person we have a constructor which is

going to take three pieces of

and it is going to pass this information

into our member variables we need to

apply a few changes here for example our

third parameter is passed as a cost

strength member type we are going to

change this to be std strength view

because this is going to save us

let's say string view here this is going

and this is going to forward information

in a way we want we're going to change

our third parameter to bhtd string view

let's say string view here we're going

to say std string view this is what we

have in our header we're going to be

having the same signature for our

we have m full name mh and we have m

address here let's try to build and see

if the error goes away sometimes visual

studio code is playing games on us

if we get a compiler error we're going

to try and fix that you see that it is

visual studio code playing with us the

we have our constructor for person it is

going to forward information using our

initializer list here we're going to

engineer class if we go there we're

going to see that we don't have any

constructor which is going to grab

information in any meaningful way and

so we are going to put in a constructor

that looks like the one we have in our

person class so we can just grab this i

like copy and pasting because that's

a few seconds so i am going to put my

constructor here only it is not going to

be called the person it is going to be

engineer and i am going to add a

member and this is going to be an

integer here to keep things simpler

implementation of this constructor in

our engineer class we can go down here

and put that in front of other

constructors let's look at the order we

header because i like to be consistent

the default constructor is first so

this constructor is going to be second

and we're going to say that it belongs

using a scope resolution operator here

and we are going to put in our

now what we want to do is to call

the constructor for person to initialize

a person part of us and then we're going

to grab the information from the

contract count and we're going to

forward that in our own member variable

the way we're going to achieve this

we're going to call the person

constructor and we're going to pass in

the full name we're going to pass the

age and we're going to pass the address

and then we're going to initialize our

own member variable which is contract

let's go to the header and look at that

we're going to see that our member

variable is contract count so we're

going to say contract count and we're

going to say contract count param we're

going to name this differently because

we don't want issues with naming here so

let's name our parameter here param

this is going to not confuse the

compiler and once we have this end we

can just put in the body which is going

initialization is now done in our

so if we do this we're going to see that

the compiler is going to be happy with

our thing here we're going to go down in

and we're going to grab the constructor

we have an engineer because we're going

to be using this as a starting point

we're going to copy it and go in our

civil engineer class we're going to see

constructor we're going to put this and

we're going to name this civil

engineer and we're going to add a

that we want to initialize so we're

std string view because we want to

forward string data we're going to say

std string view here and we're going to

say speciality and we are going to put

in our cpp file for a civil engineer

we're going to put this below our

let's grab this i lost the desk somehow

and we're going to paste down here

we're going to say that this constructor

belongs to the civil engineer class i'm

going to use our scope resolution

operator and after this we're going to

put our initializer list in civil

engineer we will call our engineer

and it is going to be taking four thanks

we're going to pass in the full name

we're going to pass in the age we're

going to pass in the address and we're

going to pass in the contract account

which we will get from our constructor

from civil engineer but we will also

initialize our specialty member

variables so we're going to say m

speciality and we're going to pass the

and this is going to initialize our then

we're going to put in an empty body and

our information is going to be properly

forwarded to our base classes so if we

build the civil engineer object proper

information is going to be forwarded to

and the proper information is going to

be forwarded to the person part of us

now that we have this in place we can

put in our htdc out statements to let us

which constructor was actually called to

build authen we're going to say that it

was our custom constructor that was

called let's say that here we're going

customer constructor called for civil

engineer we are going to go to our

engineer class and also say the same

thing let's go to this cpp file for that

and we're going to put in our htdc out

statement and we're going to say custom

constructor we can copy this to be

consistent with what we had in our

constructor default constructor i should

say and we're going to say custom

constructor called for our engineer

class we're going to go back to person

and we're going to go to the

implementation file and we're going to

copy the message from our default

constructor and we're going to put this

in and say that the custom constructor

was called for person here so now that

we have these guys in we can go to our

main cpp file and include the classes

they are included here we can try to

create a person object just like we saw

in the slides and we're going to try and

build this program and see which

constructor is called to set up this

this shouldn't be rocket science by now

we know that our custom constructor is

going to be called because we are

passing three parameters which should be

forwarded to our member variables

through this initializer last so let's

build with gcc and make sure this is

what we expect we're going to use our

the bolt is going to be good as you see

here and if we bring up our powershell

window and run rooster we're going to

see that our custom constructor is

called let's bring up the main cpp file

so that we can see our thing we are

passing this information here and we are

printing our person object and we're

going to see that the full name is jon

snow the age is 27 and the address is

winterfell called and all this gibberish

we have here our constructor is really

being called okay so this is working we

can also set up an engineer object and

see that the information is being

properly propagated to the person part

of our engineer object because engineer

we are passing the information for the

full name the age the address but we are

also passing in the contract count which

should be used to initialize the

engineer part of us so we are going to

run the task to build with gcc

the build is going to go through

successfully and we can bring up our

powershell window and run the program

we're going to see that we're going to

branch the information for person custom

constructor for person called but what

we really are interested in here

is seeing that the custom constructor

for building our engineer object and

then we call the engineer constructor

and again this falls in line with what

we saw in the last lecture the most

based constructor is called first and

then the must specialize constructor is

called last in this case we are just

setting up thanks in such a way that our

custom constructors are called and we do

that from our engineer class by calling

the base constructor explicitly

using the syntax that we have here in

our initializer list after we have the

base constructor called we are going to

initialize our own member variables and

and in this way the information for the

current class will be initialized

properly and this is what we see here i

think this is a little bit misleading

because we still have the information

the person objects that we bought

printed out here we can comment this out

and build again we're going to pass this

through gcc to build our program the

build is going to be good we can

clear and run rooster and we're going to

see that the custom constructor is

called for a person to set up the person

part of us and then another layer of

engineer is going to be set up in our

object to initialize the contract count

member variable part of us and we're

going to have the information here so if

we print the full name we're going to

get daniel gray the age is going to be

41. the address is going to be the

gibberish we expect here and the

contract count is going to be passed in

successfully and this is really cool we

can also comment this out and set up a

civil engineer object we can do that

okay so let's go down and put this in

place we're going to create a civil

engineer object we can close up

the left side bar here to have some more

breathing room we're going to build a

civil engineer object we're going to

pass in full name age address contract

count and a speciality which i think we

expect from our civil engineer custom

that's going to be an std strength

that's what we are passing in here i

should say that's going to be

a string view but we can pass in string

data just like this and the string view

so what we're going to see here we're

going to see the person constructor

called the person custom constructor i

should say we're going to see the

engineer custom constructor called and

the civil engineer custom constructor

called to pass and forward all this

in related parts of our civil engineer

object let's build and see that this is

actually going to even compile

the book is going to be good we can

and run rooster and we're going to see

that this is exactly what we expect the

custom constructor for person is going

the custom constructor for engineer is

going to be called and then the custom

constructor for a civil engineer is

and this really falls in line with what

we expect if we are building a civil

engineer object and the civil engineer

class happens to be inheriting both from

engineer and from person we're going to

have the person part of us world first

and because of this we're going to see

the person constructor called but in

this lecture the rio focus is getting

our custom constructor called so the

person custom constructor is going to be

called after that we're going to call

the custom constructor for the engineer

part of us and that's going to set up

the engineer specific member variables

in our object after that we're going to

set up another layer of civil engineer

in our object and this is going to

initialize the member variable that

belongs to the civil engineer

part of us in our object so this is

really the main goal in this lecture

showing you that you can set up fans in

such a way that your custom constructors

are called when setting up your object

as you see here okay now that we have

this working i want you to see that

there are some bad ways to do these

things and some people are actually

going to try to set things up in that

way the first bad way is to try and

initialize our member variables in the

body of the class if you do things like

this again this is going to work because

full name and age are going to be

inherited publicly from the person class

so the code here is going to work but we

have no way to initialize the address

member variable because it is private to

the person class so if we try to access

that we're going to get a compiler error

let's try this out in code and see the

actual compiler error to try this out i

am going to comment out the good code

here and i am going to copy and put in

something that is going to be

problematic as we saw in the slides i am

going to paste in my constructor here i

should close my powershell window here

and i am going to take out my

initializer lust because we're not going

and we're going to just grab the data

and use that to initialize our data in

our member variable here so we're going

to grab the full name and say m full

name equals full name we can do that

we're going to say mh equals h that's

the information we get we're going to

say m address and you see that we don't

even have that in autocomplete so we're

going to pass the address we're going to

be stubborn and ignore these squiggly

lines and we're going to say m

speciality and we're going to grab the

speciality and pass that in but you see

that line 26 has a bunch of squiggly

and the reason is the m address member

variable is invisible and not

manipulable from a civil engineer class

again the reason is that the address

member variable is private to the person

class so the civil engineer class has no

business initializing this in the body

this is not going to work so if we try

and build this we're going to pass this

through gcc we are going to see that the

world is going to finish with errors and

if we go up we're going to probably see

the error person m address is private

within this context and we have no

business accessing that in the civil

engineer cpp file at line 26 this is

what we see here and this is the

offending line we shouldn't really be

doing this if we comment out this line

this is going to work but our member

with a junk value and this is really not

good because our address that we worked

to set up in our parameter here is just

going to be ignored so this is bad you

shouldn't really be initializing your

member variables like this especially if

you have an inheritance hierarchy in

your classes so we're going to comment

this out and say that this is really bad

it's going to give you compiler errors

and some of you are going to say okay

this is not working but what if we try

to use an initializer list directly

let's see if that actually works

set up another constructor here and we

are going to set up the data in our

initializer list we're going to say

name and pass in the full name we can do

that let's try this out we're going to

and we're going to pass age we can do

that and we're going to grab the address

and we're going to pass an address here

and after that we're going to say m

spatiality and we're going to pass in

what if we do something like this but

you're going to see that we have

squiggly lines here and the problem with

this way of doing things is that the

civil engineer class has no business

that belong to the person class in the

initializer list your initializer list

only has the capability to initialize

the member variables that belong to the

current class and m full name mh and m

address don't belong to the cipher

engineer class that's why we're going to

have a compiler error if we try to set

up things in this way if we're trying to

build the program we're going to get a

we're going to see that the build is

going to finish with errors and it is

going to say expected initializer before

and we need a column column here sorry

for this so this is not the error we

expect but you see that the moment we do

this we have a bunch of squiggly lines

on full name age and address and let's

build and see the problem we have and

we're going to build with errors as we

we are going to see our errors civil

engineer does not have any field called

m full name we're going to see that

civil engineer doesn't have any field

called mh and civil engineer doesn't

have any field named m full name or m

address here that's the problem we have

no business initializing these member

variables that don't belong to the civil

engineer class in the first place so

this is also not going to work the best

bet we have already is to call the best

constructor and let that initialize the

member variables that belong to our

in the inheritance hierarchy for example

in our civil engineer constructor here

constructor to initialize the engineer

part of us and we're going to be

forwarding the information the full name

the age the address and the contract

account the engineer class is in turn

going to call its base constructor to

forward the information about the full

name of the agent the address and it is

going to initialize its own member

variable m construct count and the

information is going to be passed in

correctly and if we try to build our

class now we're going to see that

everything is going to work and i really

wanted you to be aware of this because

the moment you understand this you're

going to set up your inheritance

hierarchies in a way that is going to

make sense and you're not going to be

getting all these weird compiler errors

this is really all we set out to do in

this lecture showing you how you can set

up your own custom constructors in your

own inheritance hierarchy and at the

moment you do that you're going to get

your classes called in the order that

you expect things are going to be set up

in layers the base constructors are

going to be called in a way that you

expect and your objects are going to be

built in a way that you can print them

and see the information that you expect

set up in your object if you want you

can also use a debugger to see the

information in your thumb so we're going

to set up a breakpoint here and we're

debugging tab we're going to hit the

green button to start debugging this

program the binary is going to be set up

once the vote is good the binary is

going to be passed in our debugger and

we are going to hit our breakpoint in a

minute let's wait for this so we have

hit the break point at line 20 and if we

expand our civil engineer object in our

locals we're going to see that we have

an engineer part of us we can expand

that and see that we also have a person

if we look at person we're going to see

that the full name is we can see john

travolta which is what we are passing

here we can also look at our age the age

and we're going to also have information

if we expand this we're going to see

that the address is this gibb brush that

number 89 we can see this information

here and you can really expand and see

all these things that make up our object

for example we can see the information

about the contract count which is 31 and

it is what we are passing when we build

this object here and the speciality

happens to be road strength as we see in

our locals here you can really see all

these things we are going to stop here

in this lecture in the next one we're

going to explore how copy constructors

work in our inheritance hierarchy so go

in this lecture we want to explore how

with our inheritance hierarchies and we

will still be using the same example we

have been using in this chapter we will

have this inheritance hierarchy and we

will still be using the same example we

have been using in this chapter the base

class is going to be person we're going

to be inheriting from that publicly to

create an engineer class and we will be

inheriting from the engineer class

publicly to create the civil engineer

class and with this we want to be able

to copy construct objects and the code

we want to be running is something like

this we have an engineer object we want

to be able to create another object from

this engineer object using the syntax

here and from what we already know this

is going to call our copy constructor

the funny thing is this is going to work

by default even if you don't put in your

copy constructor the reason is the

compiler is going to insert a copy

constructor for you and things are going

to be copied in a way that you expect

because none of our classes is using

dynamic memory allocation so everything

is just going to fall in place and it is

going to work but if you happen to need

to set up your own copy constructor

we're going to see how you could do that

in this lecture and we're going to start

by the base class we're going to set up

a copy constructor for the person class

and this is nothing complicated we just

pass our parameter by reference this is

going to be our source object and we

will be copying the data from our source

object to initialize the member

variables in the current object that we

are copying here again this is a copy

constructor which will be copy

constructing from the parameter that we

pass by reference now how do we do the

constructor for the engineer class which

happens to be inheriting from person try

to think about that one way to do things

is to set up things like this and this

will be just initializing the engineer

layer of our class but nothing is going

to be initializing the person part of us

and this is bad this is going to call

the default constructor to initialize

the person part of us and we will just

be left in with junk data that is

initializing the person object by

default and all the data we have in our

parameter engineer object is just going

to be lost for the person part of us so

we don't want to do this this is bad

design you shouldn't do this some of you

are going to say but what if we call the

best constructor we have seen that we

could do that right but remember this is

a copy constructor what we have on the

if you set up a syntax like this with

the copy constructor the compiler is

going to set up a temporary person

object and a copy from that object to

initialize the person part of us so this

is going to be creating a temporary copy

object containing the same data we have

in our engineer object so to some extent

this is going to work but the problem we

still have is that we are using the m

address member variable directly from an

engineer object and from what we already

know this m address member variable is

private to the person class and we have

from an engineer construct so this is

going to give us a compiler error but

you know that it is possible to set up a

getter in the engineer class that is

going to return this address and you can

call that together here and get this

thing to initialize your data this is

going to work but this is really weird

you shouldn't do this this is bad design

there is a better way i am going to show

you but before we look at that wave

let's try and summarize the problems we

have with this way of doing things this

is not going to be reusing the copy

constructor we have worked hard to set

up in person so this is just going to be

called duplication another thing is that

the m address member variable is private

to person so if we try and use it like

this we're going to get a compiler error

again it is possible to set up a getter

that could return that and we could use

that getter in this place but this is

bad design we are really forced to set

up a getter that is possibly only used

in this place that's bad design we don't

want to do something like this another

thing is that this is going to create a

temporary copy of person from which we

will be copying to initialize the person

part of us we don't want to be making

that copy because we hate copies in c

plus plus code so the best way to do

this is to set up your copy constructor

in this way we are going to say person

and directly passing our engineer object

the compiler is smart enough to see that

we are passing an engineer object to

initialize a person object and what the

compiler is going to do is really smart

suppose our engineer object is made up

of two layers the inner layer is going

to be containing the information about

the person part of us and the outer

layer is going to be containing the

engineer part of us okay so this is the

setup we have so the compiler is going

to see that we are passing in an

engineer object to initialize a person

object and what it is going to do is

really smart it is going to strip off

all this engineer part if i can describe

it like this we're going to strip off

that we have in our engineer object and

we will be just left with the person

part that we passed then to initialize

our person object and this is really

smart and it is going to work so again

the syntax is what you see here

we say person we pass in our source

object and then we can initialize the

member variable that belong to the

engineer part of us we will be

initializing contract count and this is

going to work now that you know this

we're going to head over to visual

studio code and play with us a little

more here we are in our working folder

the current project is copy constructors

with inheritance we will be reusing the

code from the last lecture so we're

going to grab everything from that

except for the binary and we're going to

copy that and put that in our current

project let's do this and we are going

to open this bad boy in visual studio

code by dragging and dropping here and

we will have our starting point we will

have our person class the engineer class

and the civil engineer class and we will

just be doing public inheritance to make

things easier here so engineer is going

to publicly inherit from person and

civil engineer is going to publicly

inherit from engineer and this is

everything we had from the last lecture

nothing special but what we want is to

set up copy constructors in such a way

that we will be able to build objects

from others for example if we leave in

our engineer object i think this is what

we used in the slides we're going to

we want to be able to create a another

engineer let's say engineer two and

above that from engineer one the thing

that might be puzzling to some of you is

that this is going to work out of the

box even if we didn't really put in a

copy constructor but the thing is the

compiler is going to insert a copy

constructor for you but that constructor

copy so it is basically going to be

copying thanks memberwise it is going to

take the contract count from engineer

one and copy that into engineer two and

we are basically going to have the same

engineer one in engineer two let's try

and print engineer two can do that we're

going to say and two and we're going to

put this out and we are going to run the

task to build with gcc that's what we

want here and you're going to see that

it is going to work out of the box if we

bring up a powershell window and run

rooster we're going to see that we have

the data in here we have engineer full

name daniel gray that's the data we have

in engineer one but notice that we are

printing engineer two here the age is

going to be 41 and the address is going

to be exactly what we had in engineer

one and you're going to see that the

constructors are going to be called to

set up engineer 2 and the custom

constructor for a person is going to be

called the custom constructor for

engineer is going to be called and this

what we expect here but what if we want

to set up our own copy constructor and

the need to do that might arise

if we happen to be doing some dynamic

memory allocation in our classes suppose

maybe person class has some dynamic

memory allocation it has some pointer

member variable and in the personal

custom constructor we are doing some

dynamic memory allocation to initialize

that pointer we may be doing the same

thing at the engineer level or the civil

engineer level and that will force you

to set up your own copy constructor and

we're going to see how you could do that

in your classes we are going to start

with the person class we're going to go

on top and set up a copy constructor in

front of our destructor here we're going

to say person and we're going to say

const person reference source

this is the syntax you use to set up

your copy constructor you already know

this from a previous chapter and we're

going to put in the implementation for

this we're going to go in the cpp file

before the destructor or we should go

our custom constructor it doesn't really

matter where you put this and we're

going to put in our scope resolution

operator let's do person here and we

will just be copying the data from the

source person so we're going to put in

our initializer list and we're going to

say m full name we're going to grab the

name from the source person we're going

to say source m full name we're going to

initialize the age we're going to say mh

and we're going to grab the age from the

and we can go to the next line so that

we see the entire thing here and say m

address and we're going to say source

and say m address this is going to set

up our constructor and down below we can

put in our body this is going to work

but this is everything we have seen so

far this is nothing new the syntax to

set up your copy constructor you just

pass it by const reference if you don't

pass by reference here you're going to

get an endless chain of copy constructor

if this is confusing to you please go

back to the chapter on classes you're

going to see everything about this and

this is really all we need to do here to

have a copy constructor for a person now

let's do things at the engineer level

we're going to go to our engineer class

and we need to set up a copy constructor

the syntax is going to be the same we're

going to say engineer and we will be

constructing from a cost engineer object

we pass as a parameter here so we're

going to say cost engineer by reference

and say source and the problem is going

to be how we implement this thing we're

going to copy this and go in our

engineer cpp file we're going to put our

copy constructor after our customer

constructor and we're going to put in

our scope resolution operator we're

going to say engineer and we're going to

put in our body let's go below and put

that in if we do things like this this

is just going to initialize our engineer

with junk data we don't want that but

some of you might say uh-huh i don't

know how to call my base constructor but

at least i can initialize my contract

count okay let's go back and see if we

have this member variable here yes it is

called contract count we can say

contract count here and we are going to

initialize this with source contract

count this is going to work but this is

going to call the default constructor of

person to initialize the person part of

us and let's go back in our main cpp

file and see what we are using to try

things out we are building an engineer

object from another let's try this out

and see if our copy constructor is

called here so we're going to say custom

copy constructor called for engineer

we're going to put in the message and

we're going to say custom copy

constructor and we're going to build our

code let's build we're going to pass

this through gcc to see what happens the

build is going to be good and let's see

what happens we're going to clear and

run rooster we are going to see that the

constructors are going to be called to

but we see that the copy constructor for

and what i want to do to really make

this super clear is put a separator

between these two guys to really know

what is happening here i am going to put

in a bunch of dashes just like this i am

going to put in my new line character

and i am going to bolt again the bolt is

going to be good as you see here we can

clear and run rooster now we are going

to see that the default constructor for

person was called to set up the person

part of us in our engineer copy

constructor and the reason is we are not

doing anything to call the custom copy

and let's go back in person and make

sure we are printing proper information

when we get to do this right we are not

putting in any message here so we should

do that we are going to say custom

constructor or custom copy constructor

called for person but this is not called

you see that we are calling the default

constructor and this is going to

initialize our person part with junk

data if we print engineer two here

you're going to see that the full name

is none the edge is zero and the address

is none so we are basically getting the

default data we have in our person

object let's go back and really show you

default full name is going to be none

the default address is going to be none

of the edge is going to be 0 by default

and this is what we get because in our

copy constructor we're not doing

anything to get our customer constructor

in person to be called okay so this is

not going to work this is bad we don't

want to do something like this but let's

comment this out and show you another

way we might try to do things and we are

going to copy our copy constructor let's

go down and do this we're going to put

in another copy of this but we don't

want to just initialize our contract

instead we want to do something else

we're going to put a comma here and

we're going to say person some of you

might be thinking what if we call the

base constructor directly we can do

something like this we can say person

and we can say source m full name we can

do that we can say source mh and some of

you are going to say source m address

let's do that source m address and we're

going to build the person object and use

that to initialize the person part of us

we are basically going to be calling the

other person constructor that we have

which takes three parameters this

constructor here this is what we are

in our copy constructor but as we saw in

the slides this is going to have a bunch

of problems this is going to be creating

a temporary person object that we are

going to be copying from to set up the

person part of us but another problem we

have which is actually going to cause a

compiler error is that we don't have

access to the m address member variable

from an engineer constructor and this is

going to give us a compiler error let's

actually try and compile this program to

really show you this we are learning we

as many compiler errors as we can so the

world is finished with errors and if we

go up we're going to see that our error

is the m address member variable is

private to the person class and we have

no business accessing that in the

engineer cpp file at line 27 in our

constructor here and this is going to be

our offending line we can't do this one

could go in our person class and set up

a public getter method which is going to

be inherited by engineer and we could

call that to return the address let's

actually do that to show you that you

so we are going to go in and put in a

public method which is going to return

the address we actually have that here

so we can call that we can say

source get address this is going to work

this is going to set up our thumb

let's try to build because i think a

visual studio code is messing with us

here okay you see the both is good it is

visual studio code which wasn't

understanding our code here and if we

run our program we're going to see that

things are going to work exactly as we

run the program here we're going to

clear and run rooster we're going to see

that now the information is being

forwarded properly but we are setting up

a temporary person copy which we are

to then forward the data to the person

part of us this is not good design and

what we really want is the setup that is

going to allow us to call the copy

constructor that we worked hard to set

up in our base class here let's go back

to person and see that if we go up we're

going to see that we have a copy

constructor we really worked hard to set

up we wanted to reuse this in our

engineer class and that's what we're

going to see here so this is working but

and we should really try to reuse our

code as much as we can so what we're

going to do is set up a mechanism that

is going to reuse the copy constructor

we have in person and all we need to do

to get that to work we can say person

and then call the copy constructor of

person by directly passing in our source

object notice that we don't need to set

up a temporary person object we will

directly be copying from our engineer

object but this is going to do the

slicing we saw in the slides again if we

have two layers on our object the inner

layer is going to be the person part of

us and the outer green layer is going to

what the compiler is going to do the

compiler is going to see that we are

engineer object to initialize the person

part of us here and it is going to say

that we just need the red part we don't

need the green part here the compiler is

really smart so it is going to slice off

person part and it is going to use that

to initialize the person part of our

engineer object and this will be reusing

the copy constructor we have in our

person object then this is really cool

this is the optimal way to set up your

copical structures if you have an

inheritance hierarchy so let's try and

build the code again we're going to pass

this through gcc to see if this actually

works the bullet is going to be good we

can clear and run rooster we're going to

see that the copy constructor is going

to be called for person to set up the

person part of us and then the custom

copy constructor for engineer is going

to be called to set up the engineer part

of us and if we look at the information

we have in the main function you're

going to see that it is the same data

daniel gray for the full name ages 41

address is this gibberish here and the

contract count is 12 it is exactly what

we passed here and our copy constructor

is working now that we have this working

we can safely reuse the same ideas

in our civil engineer copy constructor

we can head over in our civil engineer

and set up the copy constructor so let's

close the left sidebar here so that we

see the entire thing we are going to say

civil engineer and we want to set up a

copy constructor so we're going to say

cast civil engineer here and we will be

passing this by reference we're going to

say source and we're going to put the

implementation of this in our cpp file

we can hop over there and go below our

custom constructor we can put in our

constructor here we're going to say

civil engineer and put in our scope

resolution operator and we're going to

go down and put in the body and in our

initializer list we're going to call the

copy constructor from engineer because

remember civil engineer is inheriting

from the engineer class so we are going

to call the engineer copy constructor

we're going to pass in source and again

this is going to slice off the civil

engineer port and only use the engineer

part of us to construct an engineer

object from this sliced of engineer

object we get from our copy constructor

here and this is really cool after that

we will initialize our contract count

member variable oh it is m speciality if

i remember correctly and we're going to

grab a source m speciality and we will

use that to initialize the civil

engineer part of us here let's go in and

say that the custom copy constructor is

being called here and we're going to say

custom copy constructor called for a

civil engineer what did we do here we

said engineer let's do engineer this is

what we want and we're going to say

engineer here properly sorry for this

but this is no big deal and now that we

have this in place we can actually build

civil engineer objects and copy

comment out the engineering stuff we

have and we can just put this in a black

comment and we're going to copy

construct civil engineers how cool is

that we're going to set up a civil

and this is going to be a civil engineer

and we're going to say daniel gray we're

going to put in all the data and we're

going to specify the speciality to be

road strength this is something i just

if this kind of speciality exists and we

will set up another civil engineer

object called n2 which we are going to

be copy constructing from and we will

see what happens when we copy construct

this thing here we should call our copy

constructor in civil engineer and the

things should propagate up all the way

to the person part of us and we're going

to see what happens let's build this

code we're going to pass this through

gcc as we always do the budget is going

to be good so this is good news we're

going to clear and run rooster and we're

going to see that the custom copy

constructor is called for person the

custom copy constructor is going to be

called for engineer and the custom copy

constructor is going to be called full

civil engineer and you see that things

are really propagating all the way to

the person part and we are calling and

reusing our copy constructors and this

is really cool if you go down you're

going to see that the information is

printed out correctly the full name is

daniel gray which we have in engineer

one the age is 41 the address is all

this gibberish the contract count is 12

and the speciality is road strength and

properly reusing our copy constructors

in our inheritance hierarchy this is

really all i had to share in this

lecture again the syntax you should be

using to set up your copy constructors

is what we see here this is going to be

reusing the code we have in our upper

classes in our hierarchy we will be

avoiding the temporary copies we saw

when we called the other constructor

directly and this is much cleaner it is

reusing code we have in other classes we

are going to stop here in this lecture

in the next one we're going to see that

it is actually possible to inherit base

constructors go ahead and finish up here

and meet me there in this lecture we're

going to explore the fact that we can

inherit base constructors and use them

in our derived classes we will build

we're using the same hierarchy we have

been using so we will have the person

class and we will be inheriting from

this person to create an engineer class

and that's what we're going to be using

to learn about this concept here so the

personal class is what we know from the

previous lectures we have a bunch of

member variables here we have the full

name the age and the address and we have

a bunch of constructors now we have a

default constructor a custom constructor

and a copy constructor that we set up

tirelessly in the last lecture now what

do we mean when we say that we can

inherit a constructor well based

constructors are not inherited by

default and what we mean by that is that

by default it is really not possible

to get derived classes to use base

constructors to set up things but it is

possible to tell the compiler to use the

base constructor to set up our own

objects for example we can put our

using person column column person this

is going to tell the compiler when

welding engineer objects don't use your

own constructor set up a base like a

constructor which is going to only

initialize the base member variables and

the compiler is going to see this

statement and it is going to generate a

constructor for you that looks something

like this so it is going to be engineer

it is going to be taking in the full

name the age and the address and it is

going to be forwarding the work to

initialize your object to the person

class and this is all this constructor

is going to do hopefully you can see

that this is called inheriting a base

constructor because all this constructor

is really doing is initializing the base

member variables it's not initializing

any member variable that belongs to the

engineer class so the engineer part of

us is going to be basically empty

containing junk data that we get by just

calling the default constructor and we

will only be initializing the data

belonging to the person part of us this

is really what i want you to see again

the syntax is what we see here

this is going to tell the compiler to

generate a constructor that is only

going to initialize the base member

variables but this constructor will be

callable and usable from the engineer

okay so this is really what we mean

by inheriting constructors one thing you

should know is that the constructor is

going to be inherited with whatever

specifier it had in the base class so if

our constructor was in the public scope

it's going to be inherited with public

access so we will be able to use it from

the outside and world engineer objects

if it was in a protected scope we want

to be able to use it from the outside if

it was private we won't even be able to

use it from a derived class you should

really know that so it is going to be

inherited with whatever access specifier

we had in our base class now that we

know this let's see some things you

should really be careful about the first

is that copy constructors are not

inheritable if you try to do that you're

going to get a compiler error but you

won't usually notice this because the

compiler is going to insert copy

constructors for you anyway this is

going to become a problem if you are

doing some dynamic memory allocation and

you're going to get pointers copied this

is really bad if you don't know about

this please go back to the chapter on

classes and you're going to see all the

story about shallow copying and deep

copying we talked about these things

another thing you should know is that

inherited constructors are really based

constructors and what we mean by this is

that they will only be initializing the

base member variables because they are

based constructors they have no

knowledge of derived member variables

that's why they only initialize base

member variables again as we said the

constructors are inherited with whatever

access specifier they had in the base

class and it is possible to set up your

own constructors on top of the inherited

constructors and you can use these

things another thing i should really

tell you is that inheritance

constructors is going to make your code

really confusing it is a technical

possibility but i strongly advise

against using this in your code because

it is just going to confuse people

people are going to see for example an

engineer constructor and they are going

to think that that constructor is going

to even initializing the engineer member

variables but it's not going to do that

because it is a base constructor it's

only going to be initializing the base

member variables and that may lead to

some confusion or even really bad

problems in your code so don't use this

it is just going to make things

confusing but i wanted you to be aware

of this and if you see this kind of

setup in classes out there you will know

what they mean this is just going to

inherit a base constructor and use it to

build objects now that we know this

we're going to head over to visual

studio code and play with us a little

more here we are in our working folder

the current project is inheriting based

constructors we are going to steal code

from the last lecture and we will be

using the main cpp file the person class

and the engineer class this is just

going to be enough for our purposes here

we're going to go back in our current

project and we're going to put this in

and we will open this in visual studio

code by dragging and dropping here this

is going to give us our thumb

and let's go to person and see that we

have our constructors and we have a

default constructor we have a custom

constructor and we have a copy

constructor one thing you should know is

that copy constructors are not inherited

so you will need to set up your copy

constructors explicitly if you want to

use them know that they want to be

coming from the upstream class you

should know that okay so this is the

message here now let's look at our

engineer class the engineer class is

publicly inheriting from person and it

has a bunch of its own constructors but

what we want to do is to take out all

these constructors and we're going to

take them out i think we can uh yeah

we're going to take them out let's do

that and we're going to go in our cpp

file and also take out all these

constructors here we're going to comment

them out i think we can take out all

these bad code we got from previous

lectures and we're going to just comment

out our constructors we're going to

close them all with a blog comment and

what we are going to do in our class is

using person person we're going to say

using person person this is going to

inherit the constructors from person and

now that we have this in place the

compiler is really going to generate a

base like constructor in our engineer

class in other words we're going to have

a default engineer constructor which is

just going to not initialize anything we

are going to have a custom constructor

which is going to take three parameters

but it is going to be an engineer

constructor and let's prove this we're

going to go in our main cpp file and

we're going to take out everything we

have here and we don't have a civil

engineer file so we shouldn't really

include that and we are going to create

an engineer object we can say and one

using the default constructor we can try

and print that out and you're going to

see that this code seems to work in

visual studio code we can try and build

this we're going to pass this through

set up a powershell window we can use to

and we're going to see that the default

constructor for person was called to

and the data is really junk data we have

in person so what the compiler is really

doing behind the scenes is to generate a

bezel-like constructor at the engineer

level and it is going to call the base

constructor to initialize the person

part of us so the data is just going to

be junk data we have in person and

you're going to see that the contract

count is going to be zero this is just a

default constructor which is just going

to grab whatever default data we have in

our object you see the contract count is

zero if we go back in person we're going

to see that the full name is none which

is what we see here the age is zero and

the address is none this is a default

constructor but we can even explicitly

pass in the data and that's going to

also work so we can pass in the full

daniel gray we can pass in the edge to

b23 for example and we can pass in a

junk address let's say something like

this and you see that this is going to

work even if we don't have any engineer

that takes three parameters let's go

back and you're going to see that all

our constructors are commented out but

this is working because we told the

a base like constructor for our engineer

so it is going to also have in

an engineer constructor that looks like

this constructor here which takes in

three parameters and this is really cool

and this is really crucial to understand

so again we are going to set up a

constructor for engineer so it is going

to be an engineer constructor but it is

going to be taking three parameters just

like the person constructor here and

this is the message i really want to

convey here so if we run this code

you're going to see that it is going to

work it is going to call our baseline

constructor for engineer and we're going

to have the data forwarded and but

you're going to see that the contract

count is not going to be taken into

account so it is going to still contain

some default data if we try and pass

that in we're going to see that we're

going to get a compiler error because

now we have no such constructor that

takes four parameters the only one we

have is one that is generated because of

this statement here and this is going to

be a baseline constructor which is just

going to take three parameters just like

this constructor here and another thing

i don't think i made clear enough is

that this is going to bring in all the

constructors you have notice that we

just put in this statement but it is

going to grab all these constructors we

have except for the copy constructors

which are not inherited in c plus plus

so you should really know this if we

build this code we're going to get a

compiler error because the compiler

what to do with the 45 parameter that we

have here but let's build and really

show you this you need to see this

compiler error with your own eyes let's

go in so the world is finished with

errors and we have an error saying no

matching function called to this

constructor which takes four parameters

if we take this out we're going to see

that this is going to work this is going

to use the compiler generated

as a result of this statement we have in

our code now if we will we're going to

see that this is going to work okay the

build is good can clear and run rooster

we're going to see that we have the full

name to be daniel gray we have the h2b23

we have our address which is really some

junk data and the contract count has no

data in it is just the default data we

have in our member variable here we have

no way to initialize this from a base

like a constructor but not everything is

really bad news if you don't want to be

limited by the constructors that are

generated by your compiler as a result

of inheritance you can set up your own

constructors for example we can uncover

our engineer constructor here and bring

it out of our comment we can do

something like this we can go in the

implementation file and also bring this

out of our comment section and now we

will be able to use this constructor

which is going to take the fourth

parameter here and do something with

that now if we go back in main the code

with three parameters is going to work

it is going to use the compiler

generated constructor but if we pass the

contract count to b4 this is also going

to work because it is going to be using

our own constructor here if we build the

code we're going to see that it is going

to work just fine let's use gcc to show

you're going to see that the world is

now our contract count is taken into

account this is really cool this is

really all i wanted you to see in this

lecture that you can let the compiler

generate the baseline constructor using

the syntax we have in our header here

this using statement can really show up

anywhere but it is going to inherit the

constructor with whatever access

specifier the constructor had in the

base class and you should really keep

these points in mind especially the last

inheriting constructors is going to make

your code confusing people are going to

notice that they can call constructors

that are really not going to be

initializing derived member variables

and this may cause serious problems in

your code we are going to stop here in

this lecture in the next one we're going

to explore how inheritance works with

these structures so far we have been

ignoring the structures we are going to

focus on them in the next lecture so go

ahead and finish up here and meet me

there in this lecture we're going to

focus on how destructors work with

inheritance and suppose we have an

inheritance hierarchy like we have been

using all along in this chapter so our

base class is person we have the

engineer class which is publicly

inheriting from person and we have a

civil engineer class which is inheriting

from engineer publicly so when we create

a civil engineer object we have seen

that the burst part is built first so we

are going to build the personal part of

us we are going to build the engineer

part of us on top of that and we are

going to build the civil engineer part

of us on top of that so the constructors

are going to be called in this order we

will call the person constructor first

engineer constructor after that and then

a civil engineer constructor after that

to set up our civil engineer object the

thing i want you to see in this lecture

is that the structures are called in the

reverse order to that so the most

specialized destructor is going to be

called first then we're going to destroy

the engineer part of us and the person

part of us is going to be destroyed last

so we are going to construct things in

this order from the base part to the

most specialized one and then we are

going to destroy thanks in this order so

these structures are going to be called

constructors that's the message i want

to convey here and we're going to set up

a simple example to play with us we're

going to create a civil engineer object

and we're going to see the order in

which these things are called and let's

head over to visual studio code and

actually do this here we are in our

working folder the current project is

inheritance and destructors we are going

to be reusing the code from a previous

lecture i don't think the last lecture

is a good example because we don't have

a civil engineer class so we are going

to go to the lecture before that and use

the code from our lecture or the copy

constructors with inheritance that's

going to give us all the classes we have

person engineer and civil engineer and

we need that in this lecture here so

let's grab all these things we're going

to copy them and put them in our current

which is inheritance and the structures

and we are going to open this in visual

studio code and it is going to be our

starting point here so we have person

engineer and civil engineer let's see

what we are doing and the main cpp file

we can take out all the junk here or we

can leave in the civil engineer object

we are creating here and we're going to

the constructors and the instructors are

called we're going to go to person and

make sure we have a constructor and we

have a bunch of constructors and

let's go to the cpp file and see that we

have messages in our constructors this

what we expect but we want to also put a

message in the destructor let's say sddc

out and say destructor for person called

this is going to do we're going to go in

our engineer class we're going to see

that we have a bunch of constructors we

have a destructor here we're going to

and make sure we take out the bad code

here because we don't really need that

we only need good code and we make sure

that we have output statements in our

constructors to know when they are

called looks like we are good we're

going to put an sddc out statement in

our destructor for engineer or engineer

called this is going to do and we are

going to hop over in our civil engineer

class we're going to have a bunch of

constructors we're going to have a civil

we can go in the cpp file and make sure

that we have output statements in our

civil engineer constructors looks like

we are good here we can take out all the

bad code we don't need and we are going

to put a message in our destructor here

so let's do that the the structure

called for civil engineer i think this

is going to be good enough let's go back

and make sure we have the same messages

and we have a destructor for person

called message and we're going to try

constructors and destructors are called

this is the order we want to make sure

we understand if you want you can even

use a debugger to follow things but i am

not going to do that here i am just

going to weld and show you the output

hopefully that's going to be proof

that things happen in the order that i

just described in the slides the build

is good we can clear we can bring up a

powershell window and then clear and

we're going to run rooster we're going

to see that the constructor is going to

be called for person for civil engineer

and you're going to see that things are

going to happen from the must-based

constructor to the most specialized

constructor so we are going to call

person engineer and civil engineer but

you're going to see that the structures

are going to be called in the reverse

the most specialized the destructor is

going to be called the first then we're

going to call the distractor for

engineer then we're going to call the

destructor for the base class so things

are going to be happening in reverse

order we will build thanks starting from

finish by the most specialized class

which is doing the inheritance and then

we're going to call the destructor for

the most specialized class first and

then the destructor for the most based

class is going to be cold last you

should really make sure you understand

this because sometimes your things are

going to be depending on this order and

you need to understand this and this is

really the main message here that the

structures are ridiculed in the reverse

we are going to stop here in this

lecture in the next one we're going to

see that we can actually reuse names in

our inheritance hierarchy and we're

going to see how that works out in the

next lecture so go ahead and finish up

here and meet me there in this lecture

we're going to see that we can reuse

names in our inheritance hierarchy

and what we mean by that is that we can

have a parent class for example and have

a child class inheriting from the parent

class and have exactly the same names

for the member variables and types or

the same signatures for functions for

example in the parent class you see that

we have a member function called

printfur it is going to be printing some

information we can have a function named

exactly the same in the child class and

c plus plus is going to allow this we

can also do the same things for member

variables for example we have m var

which is of type and we have exactly the

same thing in our child class and c plus

plus is going to allow this now the

problem is if you create an object of

child which method will be called if you

what c plus plus does is it is going to

things you have in the base class if you

happen to set up exactly the same thing

in a derived class so for example the

members in our child class are going to

hide the members we had in the base

class and if we call these methods on a

child object we are going to get the

versions in the child class called if we

call these methods on a parent object we

are going to get the parent version

called and we're going to see the data

in the parent class printed out this is

the message here it is possible to use

the same names in both parent and child

classes and if you do that things in

child classes are going to hide or

override what we had in the parent class

this is the message i want to convey

here and here is a simple example to

drive home how you can use these things

for example we can create a child object

and if we call a method on the child

object this is going to call the method

in child but it is possible to force the

compiler to call the version in the base

class and you're going to see this

syntax used somewhere in your code out

there so the syntax is to say the object

name you put it up you say the name for

the parent class and then you call the

method using the scope resolution

operator here and this is going to hold

the method in the parent okay now that

you know this we're going to head over

to visual studio code and play with this

a little more here we are in our working

folder the current project is reused

symbols and inheritance we are going to

just grab the template files because we

are going to be building things from

scratch here and we're going to put in

our files no big deal here and we can

open this in visual studio code this is

going to give us a bare minimum main cpp

file we can clean it up a little bit and

we're going to set up our parent class

let's do that pretty fast we're going to

say parent and set up the header and

we're going to set up the implementation

cpp file we are going to set up the

header file and this is going to do

everything we want we have a constructor

which is really defaulted here so let's

say default and we cannot default the

destructor can we default it let's do

this and see what happens and we don't

really need to do anything in the cpp

file we can leave it empty this is not

going to hurt anything and with this we

can create parent objects let's do that

we're going to hop over to the main cpp

file and include current and make sure

that we can use that and we're going to

create a parent object let's do that

we're going to say parent p1 and say

p1 print values we can do that and we

can work and run this program i think it

is going to work just fine okay the

build is good we can clear or we can set

up a powershell window and a clear

and run rooster this is going to say the

value in parent is 100 which is what we

have by default here we have a simple

member variable which is of ant type it

is protected because we want it to be

inherited and we have a bunch of

constructors here we have a constructor

which is going to take a value but we're

not going to use that here the default

is just fine you can use that if you

want and we have a member function which

is going to print the value in parent

now that this is working we can set up a

child class which is going to be

inheriting from the parent class here so

let's do that we're going to set up the

child header file child dot h and we're

going to set up a cpp file for that that

cpp so we are going to put the data in

the header file again it is nothing

complicated it is just a simple class

which is going to be inheriting from

parent and we are going to have our own

member variable which is going to

eclipse what we had in the parent so the

names here must be the same m a member

of r if we go in parent it is m member

for and what we have in child is going

to eclipse what we had in the parent

class in other words if we print the

member variable in child we're going to

see 1000 printed out here we want to see

100 that we have in the parent printed

out hopefully this is going to drive the

point home that if you have members

what you have in your derived classes is

going to eclipse or hide what we had in

the parent class this is the message

here but even if this is the case c plus

plus allows us to specify that we want

to grab the data in parent from a child

object for example in our show values

method we can print the value in child

directly using m member war but we can

also specify that we want the value in

the parent class because even if this is

a child object it has a current part of

it so we can access the data in parent

and print that if the data happens to be

accessible from our derived class and

that's why we set up our member variable

to be protected for it to be accessible

in our derived classes this is going to

allow us to print something like this

and this is going to really work now

that we have this in place we can go in

and only include the child we can do

that and we're going to create a child

object or we can just take out

and adjust putting the code we can use

to play with this things we can create

and on this child we can print for we're

going to see that the data is going to

be printed out but we can also use this

syntax to print the data in the parent

part of us and we're going to see that

the data is printed out we can also show

the values and make sure we see this

from a member function of the child

class this is going to call this member

and we're going to get to the value in

child and we're going to get the value

in parent printed out on the console now

that we have this we can actually try

and work this we're going to use gcc to

we're going to see that we're going to

finish building with errors what is the

problem here we have an undefined

reference to child destructor

we didn't put in a definition for the

child destructor so let's go there

and default it we can do that we're

going to say equals default and the

compiler is going to generate one for us

and now if we build we're going to build

with gcc again the bolt is going to be

good you can clear and run rooster and

we're going to see that the value in

child is 33 because we passed that in

explicitly and this is going to call the

constructor we have in child that

happens to be this guy here and you see

that we are really keeping things simple

we are not calling the base constructor

here the compiler is just going to call

the default constructor we have in

parent here and this is going to just

work the main message here is that you

can set up member variables and member

functions named exactly the same way in

the parent class and in child classes

and what you have in your derived

classes is going to hide what we have in

our current classes so if we call a

method on a child object for example

like we are doing here this is going to

call the method in child but we still

have the ability to call data in the

parent part of us and this is what we do

here i would like to welcome you in this

new chapter where we're going to be

learning about polymorphism and

polymorphism is the setup we can do in

to use a base pointer and manage derived

objects suppose we have an inheritance

hierarchy like we have here we have

shaped as our base class and we can

inherit from oval and create a circle

class imagine that we can create all

kinds of crazy shapes that inherit from

shape in our simplest path program for

example we have a rectangle class we

have a triangle class we have all kinds

of crazy shapes now if we have this

inheritance hierarchy here is something

we might want to do we might want to set

up a base pointer that is managing a

derived object and set up code like this

for example we say shape pointer and i

set up a pointer variable here and use

this pointer to manage a circle object

that we dynamically allocate for on this

line here we can also do a shape pointer

that is managing a rectangle we can set

up a shape pointer that is managing a

novel object we can really set up a base

pointer that is managing any kind of

object we support in our inheritance

hierarchy now some of you are going to

ask a few questions one of them is going

to be is this even legal c plus plus

syntax and the answer is yes because if

circle is inherited somehow from shape a

circle is really a shape and if

rectangle is inheriting from shape it is

a shape and if we try to assign a circle

to a shape we're going to see that

that's going to work so this is valid c

plus plus syntax and we can do the same

thing using references as we see here we

can set up a reference that is going to

a circle object that we have through

circle one we can set up a reference to

manage a rectangle that we have in shape

two we can set up a reference to manage

an awful object we can really do all

why would we want to do something like

this now try and think about your

inheritance hierarchy here and try to

think about what if you want to

draw this kind of ship for example if

you didn't use polymorphism you would

need to set up all kinds of crazy

methods to draw each kind of object and

we have no way around this because these

are different types if you have a method

that takes a novel and you pass in a

circle that's going to give you a

compiler error but with polymorphism we

can set up a single method which takes a

shape pointer or a shape reference

and we can pass in all kinds of crazy

objects whose class derive from shape so

for example we can pass in the address

of the circle and this function is going

to draw a circle we can pass in the

address of a rectangle this is going to

draw a rectangle we can pass in the

address of a novel and this is going to

draw a novel hopefully you can see how

this is useful we can even do this using

references so if we pass in a rectangle

this is going to draw a rectangle if we

pass in a circle this is going to draw a

circle you get the idea this is one of

the benefits of using polymorphism again

polymorphism is about using base class

pointers or references to manage derived

objects in our inheritance hierarchies

another benefit of polymorphism is to

allow us to be able to store

different kinds of objects in a single

collection remember an array can store

objects of different types if you say

tap an end array and try to store in a

string or a double you're going to get a

compiler error because that's not

allowed so if you have an array that is

going to store circles you can't put in

a novel you can't put in a rectangle you

can put in a star you can't really do

that because an array by design is going

to store objects of the same type but we

can avoid this limitation using

polymorphism again we can set up an

array that is going to store base class

pointers and we can store in all kinds

of crazy objects whose class derived

from this base class here so here we can

store in a circle object we can store in

a novel we can store in any kind of

object that is part of our inheritance

hierarchy with the base class as shape

and this is going to work and this is

going to be using polymorphism for

example if you look through this

collection calling the joe method for

the first element this is going to call

the draw method on the circle for the

second element we're going to call the

draw method on a novel and this is going

really cool this is something we can

achieve with polymorphism and i want to

back up a little bit and talk about what

is really meant by polymorphism

polymorphism really means multiple forms

and in my opinion what this means is

that the base class pointer or base

class reference can take multiple forms

at one point it might be managing a

circle at one point it might be managing

a rectangle at one point it might be

managing a novel object so it is a basic

pointer but it can take multiple forms

because it can be managing multiple

kinds of objects whose class are part of

our inheritance hierarchy this is what

we mean by polymorphism so again the

idea is that we can use the base class

pointer or reference to manage all kinds

of crazy objects in our program and this

is going to have many benefits as we are

about to experience in this chapter here

i am really excited to be explaining

this to you this is one of the most

powerful features in c plus plus we are

going to start in the next lecture and

show you that you don't get polymorphism

by default in c plus plus and what you

get is static binding go ahead and

finish up here and meet me there

manage derived objects in our c plus

plus program hopefully this is going to

give you a clear idea on why we might

need to do this so let's look at our

classes that we're going to be using

here we're going to set up a shape class

which is going to be representing our

shapes this is going to be our base

class that's the basic use for this here

it has a simple member variable which is

going to store the description for our

shape it is also going to have our draw

method which is really not going to draw

anything it is just going to say the

description for our shape here once we

have this shape we can create other

shapes from it for example we can create

a novel class which is going to be

representing a shape like this it is

going to have two member variables one

is going to be mx radius the other is

going to be m y radius this may

the radiuses for our oval here for

example the x radius might be something

like this the y radius might be

something like this and this is how

we're going to be representing

this shape here we also have a draw

method which is going to print the

information about this shape here it is

going to say the description that we're

going to be inheriting publicly from

shape but it is also going to say the

radius information for this shape it is

going to give us the x radius and the y

radius here and we have a bunch of

constructors here we have a default

constructor which is really not going to

do anything we also have a constructor

that is going to be taking two

parameters to forward the data in our

member variables here this is the kind

of class we're going to set up in our

program we also have another derived

class from oval and this is going to be

a circle class it is going to be a

specialization on oval in which both x

and y radius are equal so the x radius

is going to be something like this and

the y radius is going to be something

like this and both of these are going to

be equal so this is going to give us a

circle shape we also have a draw method

which is going to print the description

and the radius we can really pick any

radius we can pick the x radius we can

pick the y radius they are really going

to be the same because they are equal

for our circle shape we also have a

simple constructor which is going to

take the radius and we are going to be

to forward the data to our oval part of

us and we're going to be setting this as

both x and y radius this is the setup we

have here okay now that we have our

inheritance hierarchy we're going to try

and use it and really explore the idea

of static binding in c plus plus

inheritance hierarchies so here we are

objects of our classes we have a shape

object we have an oval object and we

have a circle object we are going to go

through a base pointer and try to manage

in our first line we're going to set up

a shape pointer and we're going to store

in the address of shape one and what we

would want in our c plus plus program is

that if we call the draw method on this

shape pointer we would want the shape

draw method to be called because we have

a shape object stored in our base

pointer here or in other words we are

using a base pointer to manage this

object in memory down here we store a

novel object in our shape pointer or in

other words we're going to be using this

base pointer to manage an actual oval

object in memory and the setup we want

is that if we call the draw method on

this shape pointer now we are going to

get the oval draw method to be called

and down here we have another example

where we are using this base pointer to

manage a circle object we are going to

store the address of the circle object

in this base pointer this is how we do

a draw method on this base pointer we

want the circle draw method to be called

so with polymorphism what we really want

is to call a method on the base pointer

and get the most specific possible

method called on our pointer this is the

setup we want but this is not what we

get by default in c plus plus if we

happen to do this and run our program as

is now with the current knowledge that

we have on the first line here we're

going to get the shape draw method

called this is what we want but on the

second example here we will see that we

see the shape draw method also called

and on this line we will also see that

we get the shape draw method to be

called this is not what we want and this

is static binding so what is happening

here is the compiler is looking at the

type of the pointer and it is using that

to decide which draw method to call so

the compiler is so the compiler is

basically saying i have a shape pointer

so i am going to call the joe method on

the shape class down here it is going to

see that it also has a shape pointer and

it is going to call the draw method on

shape and down here it is going to see

that it has a shape pointer and it is

going to call the jaw method on the

shape class this is what static binding

is all about the compiler is going to

resolve the joe method statically and

what that means is that the compiler is

going to look at the type of the pointer

that we have and it is going to use that

to decide which joe method to call in

our inheritance hierarchy so this is the

default and it is called static binding

in c plus plus we also get the same

behavior if we try to use a base

reference to manage our actual object in

memory here we have the same kinds of

objects we had in a previous slide and

we are using a base reference to manage

our object and what we really want is

that if we go through a base reference

to call our draw method we will get the

most specific draw method called so if

our base reference is managing a shape

we will get the shape draw method called

if our base reference is managing an

alpha object we want the oval draw

method to be called here and if our base

reference is managing a circle object we

want the circle joe method called here

this is what we want but again the

compiler is just going to look at the

type of the reference so for the first

line here it's going to say i have a

shape reference so i am going to call

the shape draw method that's what we're

going to get here on the second line

here it's going to say uh-huh i have a

shape reference so i will call

the draw method of the shape class

that's what we're going to see here by

default and on this line here it is

going to say i have a shape reference so

i am going to call the draw method on

the shape class and this is the behavior

we get by default and this is static

binding in action okay so now that we

have seen what static binding is all

about let's re-examine the idea of why

we need polymorphism and i am going to

give you a simple example here suppose

we have a bunch of shapes we manage in

our programs and we want to draw all

these shapes if we want to draw a circle

with the current setup we have we would

set up a draw circle method if we want

to draw a novel we would need to set up

a draw over method and this will call

our circle draw method and this will

call our oval joe method this is going

to do what we want but try to think

about this if we have 100 shapes in our

program we will need to set up 100 such

methods and this is a mess i don't think

you want to do something like this

and we have another simple case that i

want you to consider suppose we want to

store all these objects in collections

and we're going to use an array to try

and drive this point home here if we

want to store these guys in collections

we will need to set up different

collections because as we have it now we

can't store different types in an array

so what we would need to do now is to

set up an array for circles and set up

an array for ovals and do more

collections for different kinds of

shapes that we support in our program

and if we want to draw them we have no

choice but to set up different kinds of

loops and each of these loops is going

to be looping on each of these

collections here hopefully you can see

that this is by design we don't want to

do this we want to set up something that

is really easier to manage in our

program and polymorphism was

and polymorphism and c plus plus was

designed to exactly solve this kind of

what we really want in our c plus plus

programs is to set up one draw method

for example we can give it a base

pointer and it doesn't matter which kind

of object we pass it when we call this

we will get that method to be called at

run time when we actually need to draw

this shape if we pass in a circle this

is going to draw the draw method on a

circle if we pass in a novel it will

call the draw method on our oval object

if we pass in a rectangle for example it

is going to call the draw method on our

rectangle object this is what we want we

also want the same kind of setup if for

example our functions are taking

reference and this is what we're going

to get this is what we want with

polymorphism and this is really going to

improve on the design that we had

earlier when we needed to set up a

specific method for each shape and we

would end up with hundreds of draw

methods and that's really bad it's not

manageable this is also going to solve

we really need to set up one collection

which is going to be taking into account

all the ships that we manage in our

inheritance hierarchy so the setup we do

is something like this we're going to

set up an array that is going to be

storing pointers to shape and we can

store in the address of a shape we can

store in the address of a novel we can

store in the address of the circle

because if you really think about it a

circle is a shape a novel is the shape

and the shape is the shape so this is

going to work and when we get to loop

through this collection and call the

draw method for the first item here we

will call the draw method on the shape

for the second element here we will call

the joe method on the oval object and

for the third element here we will call

the draw method on our circle object and

we will draw a shape a novel and a

circle with just one loop and this is

really cool this is the design we want

now this is not the default behavior we

get in our c plus plus classes if we set

up an inheritance hierarchy

with our draw methods what we get by

default is static binding but we will

see how we can get dynamic binding or

polymorphism in the next lecture for

this one we're going to explore static

binding and we're going to head over to

visual studio code and play with us a

little more here we are in our working

folder the current project is static

binding with inheritance we are going to

grab our template files this is going to

be our starting point here we're going

to put in these files and i am going to

put in our classes to save time

if you want you can download these

resource section on this lecture you're

going to find them and you can use them

as a starting point this is going to

save us a few seconds because we don't

really want to type these classes you

already know how to create classes if

you made it this far in the course so i

am going to drag this and drop here to

open in visual studio code and this is

going to give us a good starting point

here we have a base class which is our

shape class it is going to have a simple

member variable which is going to be the

description one thing i think we need to

improve on this is to use a string view

so let's include string view we can

include that here we're going to say

include string view because we are using

modern c plus plus and we're going to

change this to be an sdd string view by

value we can do this okay so we have our

class here and we have a draw method

which is really not going to do anything

special it's going to just print the

description here and we're going to see

it printed out on the output stream

if we look at the cpp file we just have

an implementation of our constructor and

we have a destructor we're going to fix

our parameter here to make it an std

string view let's look at our oval class

and we have a bunch of member variables

here two to be exact one is going to be

the x radius the other is going to be

our y radius we have a constructor here

which is going to be taking three

parameters two parameters for the data

for our radius here and we have a

third parameter which is going to store

our description data we're going to also

change this to bstd string view and this

is going to do we have a draw method

which is going to be printing the

description and our radius data and this

is really it we don't need anything

fancy here let's look at our oval cpp

file it is going to have the

implementation for our constructor

we just need to change the type for our

description here and make this an sdd

string view let's do this and we will

look at our circle class which is going

publicly it won't have any member

variable because it's just going to

forward the data to the over portoverse

it doesn't really need to do any other

specialization but what we need is a

method which is going to return the

radius because we want to print that

here so we can head over in our oval

class and set up a protected section

which is going to give us these methods

here so i'm just going to put them in

here to save on some time it is

protected because we want this to be

usable in derived classes but we don't

want this usable from the outside this

is the setup we can achieve by making

these guys protected here get x rad is

going to return the x radius get y rad

is going to return the y radius they are

const because we don't intend for this

to modify our object and if we go in our

circle class this is going to work now

information on our circle object and we

will see on our output stream if we look

at the implementation of our circle

class it is nothing complicated it is

just going to take the double radius and

it is going to forward the data to the

oval part of us and our description here

to take into account that we want to use

std string view here so let's change

this to bhd string view we can do that

and we are going to head over in our cpp

file and change that as well std string

view you can do that and now our classes

are really complete we can head over in

our main cpp file we can clean that up a

little bit and we're going to remove

we are going to include our classes so

we're going to include shape let's do

we are going to put in oval let's do

that oval dot h and we are going to put

in circle and we are going to create

objects of these classes and try to

print their information so we're going

to set up a shape called the shape one

we're going to set up a novel called

oval one we're going to set up a circle

called circle one and we're going to see

what kind of information we see

if we try to call the job method again

in shape the draw method is just going

to say that we are calling shape joe

in alvo we are going to say that we are

drawing an oval and we're going to say

the description and the radius in circle

we're going to say that we are calling

the draw method on the circle object and

say the description and the radius here

this is the information we want so we

are going to try and build this program

using gcc our favorite compiler you can

really use any compiler you have your

hands on but we are going to use gcc

here because it is our favorite and

we're going to have a bunch of errors

what it is that we have here what is it

that we have here let's go in shape

at line 4 and see what we have and we

have a j here that we don't want let's

take this out and we're going to build

it and we're going to pass this through

gcc and the bolt is going to be good we

can bring up a powershell window to run

our program let's run rooster and we're

going to see that shape draw was called

drawing shape one you see we have just

created shape one here and we are

we are going to call the oval drill

method and we're going to print

the information on that you see that it

is over one here and we're going to put

out our radius data x radius is going to

be 2 as we specified here y radius is

going to be 3.5 and this is our

information we are also going to call

the draw method on our circle object

this is what we get and we're going to

say we are drawing circle 1 and the

radius is going to be 3 3 this is our

information here but we don't want to go

through direct objects to manage our

data here what we want is to either go

through base pointers or base references

so we are going to set up a shape

pointer let's do that we're going to say

shift because that's our base class and

shape ptr to represent our pointer and

we're going to store in the address of

shape one we can do something like this

and that's really see what is happening

we're going to comment out our calls to

draw methods here and we're going to see

what happens so if we say shape ptr and

call the draw method we can do that

let's try and build our program

we're going to pass this through gcc

you're going to see that it is going to

work and it is going to do what we

expect if we run this program here you

can clear and run rooster we're going to

see that shape draw was called and we

are going to be drawing shape one here

this is what we expect but if we go down

and say we don't want to call the draw

method here we are going to store in

let's say shape ptr and we're going to

store in the address of our over one

and we want to call the draw method here

now if you do this as we saw in the

is to get the draw method on our actual

oval object called and if we will for

example drawing things on the screen we

would draw a novel this is what we want

here but this is not what we're going to

get you're going to see that we still

job method from the shape class called

and it is going to and it is going to

say drawing over one let's try and build

this program and i really want you to

see this so the builder is good we can

clear and run rooster you're going to

row even if we are storing again

object so this is the default behavior

we get and this is static binding that

we get by default in our inheritance

hierarchies so what the compiler is

really going to do here it's going to

look at the type of the pointer that we

have here it is going to say i have a

shape pointer so i am going to call the

jaw method on the shape type that i have

in my pointer here and we are going to

that this is calling the draw method on

our shape and this is not what we want

in most cases we are going to see that

we get the same behavior if we store an

a circle object let's do that we're

going to say shift pointer and we're

going to store in the address of our

circle one and then we're going to call

our draw method on our shape pointer

again this is going to draw a shape it's

not going to draw a circle that we

really are managing with our base

pointer here and some of you must be

why are we able to store circle pointers

for example in a shape well a circle is

a shape according to our inheritance

hierarchy if we take a closer look again

here you're going to see that oval is

going to be inheriting from shape

and the circle is going to be inheriting

from oval so from what we learned in the

oval has a shape part in it and the

circle has a novel part in it which in

turn is going to have a shaped board in

it so from this understanding it

shouldn't really be surprising that we

novel object with a shape pointer or the

fact that we are able to manage a circle

using a shape pointer this is why we are

able to do something like this okay so i

hope this is super clear but again we

are not getting the default behavior

that we want but we will see how we can

achieve that in the next lecture for now

i really want you to understand what

static binding is all about and it is

the fact that the compiler is going to

look at the type of the pointer here and

use that to decide which method it is

in our inheritance hierarchy the

compiler for example is going to see

that we have a circle object stored n at

lineup 25 here but when it wants to

decide which joe version to call it is

going to look at the type of this

pointer here and it is going to use that

to decide which draw method to call and

in this case it is going to call the

shape version because the type of this

pointer is shape okay so i really hope

this is super clear here we are going to

get the same behavior if we try to

manage our objects using references for

example if we go through a shape

reference let's do that we're going to

say shape reference and say shape ref

and we are going to store in shape one

and we want to call the draw method on

ship reference let's do that so let's

call the joe method and you're going to

see that we will get the shape method

and this is really making sense because

managed by this reference here so if we

build our program let's do that we're

going to pass this through gcc

you're going to see that we get what we

expect the build is going to be good

we're going to clear and run rooster and

we see shape drill called this is what

we want but if we use this reference to

manage derived object for example let's

put in over one we can do that we're

going to see that we don't get the most

specific draw method for oval here

called we will still get the method

for a shape called let's build and show

you this this is static binding again

okay the build is good we can clear and

run rooster we're going to see that

shape draw it is drawing we don't get

the ovo draw method called we get shape

drill method again the compiler is going

to look at the type of this reference by

default and it is going to use that to

decide which draw method to call if we

even put in a circle we are going to get

the same behavior let's build with gcc

the bolt is good we can clear and run

rooster we see that shape draw is called

what we want okay so this is static

binding and it is the default behavior

we get if we have an inheritance

hierarchy with the same method spread

across each derived class we're going to

get the shape version called even if

what we are really managing with a shape

pointer or a shape reference is a

derived object i really want you to

understand this now let's see why this

is really badly designed by default in c

plus plus if you happen to need to pass

ship parameters to functions for example

we might do something like this we might

need a function to draw a circle we

might need a function to draw a novel

and if you happen to have 100 objects

you can draw in your program you have no

choice but to set up 100 drawing methods

or functions this is really bad design

you don't want to do something like this

so what you would do in your program for

and you would say for example draw

circle and pass in a circle and say draw

oval do we have a draw or full function

let's see yes we have that we can go

down and say draw oval and pass in our

oval one this is going to work just fine

but hopefully you can see that this is

bad design if you have a lot of shapes

in your program this is going to quickly

become and manageable and you don't want

to do something like this what we want

to only have one method and get to the c

plus plus runtime to resolve which one

is called at runtime when we get to pass

our actual objects and we will only have

one function which is going to take into

account hundreds of shapes that we might

potentially have in our c plus plus

program this is going to be much easier

to manage and we will actually be able

to achieve this in the next lecture so

stay tuned for that another problem with

us is if you happen to need to store

these shapes in collections if you need

to set up something like this you will

have no choice but to set up different

collections for each type for example we

might set up a collection for a circle a

collection for oval and here we are just

using arrays to model our collections

this is really bad design if you happen

to have 100 shapes in your program you

will set up 100 such collections and the

only difference is that they are just

different types and this is really bad

design because even if they are

different types they are related and

they are all shapes in our c plus plus

program and what we really want is to

set up one collection which is going to

take into account all these kinds of

shapes that we might have in our c plus

plus program and we will be able to

achieve this again in the next lecture

but the whole point of this lecture was

to show you static binding that we get

by default with our inheritance

hierarchies static binding may be bad if

you really are managing a lot of related

objects in your c plus plus program

and all these objects have the same

that each derived class is specializing

but you want the most specialized method

to be called on the actual object that

you are managing with a base pointer or

a base reference hopefully this is super

clear i apologize this lecture turned

out to be really long but i wanted you

to make this super clear and everything

else we do in the reminder of this

chapter is really going to fall in place

so make sure you understand this and if

you have a problem do you ask me i will

do the best i can to help you out this

is really all i had to share in this

lecture i hope you found it interesting

we are going to stop here in this

lecture in the next one we're going to

show you how you can achieve dynamic

binding using virtual functions in c

go ahead and finish up here and meet me

there in this lecture we're going to see

how we can achieve dynamic binding or

using virtual functions in our

inheritance hierarchies in the last

lecture we had a hierarchy like this

where the base class was shaped we had

an overclass which was publicly deriving

or inheriting from shape and we had a

circle class which was publicly

inherited from over and the problem we

had was that if we happen to be managing

shape pointers or shape references we

don't get the correct methods called if

on our base pointer or base reference

and this was really bad and this is

something we want in practical c plus

plus programs i am here to tell you in

this lecture that you can just achieve

by doing a tiny modification on your

inheritance hierarchy all you need to do

is to mark the methods you need to be

virtual and we do that by inserting this

virtual keyword in front of our function

so we're going to do that on our shape

class we're going to do that on our over

class and we're going to do that on our

circle class once we do this the c plus

plus compiler is going to know i want to

be looking at the type of the pointer or

reference to know which kind of method

to call and my inheritance hierarchy if

i happen to be using a base pointer or a

base reference to manage a derived

object and we're going to be making this

super clear in a minute and if you are

lost please bear with me you're going to

understand so let's do this we're going

to modify our shape class and change our

as you see here we're going to head over

in our oval class we're going to modify

our draw method and mark it to be

virtual using the virtual keyword here

and we're going to move in our circle

class and change it to be virtual as you

see down here this is really all we need

from what we had in the last lecture and

this is going to be magic let's look at

what we can achieve now we're going to

set up three objects shape oval and

circle as you see here and we're going

to be calling our method which is going

to be taking references and we're going

to see that we get the correct most

specific method called so for example

here we will call the shape joe down

here we will call the oval draw method

because we just passed in a novel object

and on the third line here we will get

the circle joe method called and we will

see it printed out on the console this

is really cool this is what we want to

achieve if we want to call our methods

that take pointers we can do that and on

the first line here we will call shape

draw on the second line here we will

call overdraw and on the third line here

we will call circuit draw this is what

we want to achieve and if we happen to

be setting up a roll base pointer like

a derived object like this or another

way to say this if we happen to be using

this base pointer to manage a derived

object and we call the draw method on

the base pointer the compiler is going

to know that it will need to resolve

this draw method dynamically the reason

is this is a virtual method and if a

method is virtual the compiler want to

static binding like we did in the last

lecture the compiler is going to be

doing dynamic binding and with dynamic

binding the compiler is not going to

look at the type of the pointer it is

going to look at the type of the actual

object that the pointer is managing and

this is going to give us the behavior

that we wanted starting from the last

lecture okay now that you know this

we're going to head over to visual

studio code and play with us a little

more here we are in our working folder

the current project is polymorphism with

virtual functions we are going to be

reusing the code from the last lecture

because that's going to give us

binary file here which is rooster and

we're going to copy everything we want

we're going to put that in the current

project and we're going to open this in

visual studio code we are going to have

our main cpp file with a bunch of

and we will just need to modify this a

little bit to achieve dynamic binding as

we saw in the slides all we need to do

is to mark all these draw methods as

virtual so we're going to say virtual

void draw in the shape class we're going

to go in the oval class and do that

we're going to mark our method as

virtual and we are going to go in our

circle class and mark our draw method as

virtual let's do that and at the moment

we do this we're going to get dynamic

binding behavior in our inheritance

hierarchy here and this is really cool

so let's go back and try to play with

what we had before i am going to comment

out everything we had and we're going to

be doing things in step here let's go

through the code that uses base pointers

that's where we started out from in the

mark that here let's put in some space

to make it easy to follow so we are

going to uncomment the line here that

calls the draw method when we have a

shape object stored in our base pointer

or when we are using a base pointer to

manage a shape object here we can also

comment out all these lines because we

don't want this to do anything

and let's see yes this is what we want

we are setting up our shapes and we are

using a base pointer to manage an actual

shape object and if we call the draw

method we expect this to call

shape draw and this is what we're going

to get let's build our program we're

going to pass this through gcc our

favorite compiler the build is going to

be good we can bring up a powershell

window we can use to play with us if we

call rooster we're going to see that

shape draw is called and we are drawing

shape one now if we change this to

manage an actual oval object we can do

that we can do that through this line

here and we expect this to call overdraw

and because the draw method is now

virtual this will use dynamic binding

again with dynamic binding we are

telling the compiler don't look at the

type of the base pointer look at the

type of the actual object that the

pointer is managing and the compiler is

going to see that this object is a novel

the oval version of the draw method here

and this is really cool this is what we

want let's run the task to build with

gcc again the world is going to be good

as you see here we can clear

and if we run booster look at this

overdraw calls and we are going to be

drawing our oval object and this is the

data we have inside we can use this

radius data to draw this on the screen

if that's what we are after in our c

plus plus program and this is really

cool we can even use our base pointer to

manage a circle object we can do that

and if we do that and call the joe

method because this draw method is now

virtual the compiler will note that it

doesn't need to look at the type of the

pointer that we are using to manage our

the compiler is going to look at the

type of the actual object that the base

pointer is managing and in this case it

happens to be a circle object so here we

will call circle draw and this is going

to draw a circle on the screen and this

is really going to be super cool so

and we're going to see this in action

the build is going to be good we can

clear and run rooster and you see that

we are drawing a circle and this is

really cool and just using virtual

functions we can really achieve powerful

features and you see that this wasn't

really hard to achieve all we had to do

was to mark our inherited methods as a

virtual and this is going to tell the

compiler to do dynamic binding and this

is going to be super cool let's see that

we can also achieve the same thing using

base references i am not going to run

base reference i am not going to be

running the code where we are using a

object because that's going to be really

boring but what we can do is put in an

awful object for example you can say

over one and say shape ref and call the

draw method again this is dynamic

binding because the draw method is

virtual so the compiler is not going to

look at the type of the reference to

decide which version of the draw method

to call it is going to look at the

actual object that this reference is

managing and it is going to see that the

type of the object is awful so c plus

plus is going to call the oval version

of the draw method that's what we're

going to get if we run this program here

let's build and see this we're going to

pass this through gcc the voltage should

be good as we see here we are going to

clear and run rooster you see we are

drawing oval if we happen to be using

this to manage our circle object let's

we will see that we will get the circle

method called okay let's build and we're

going to pass this through gcc to do

that the both is going to be good we can

clear and run rooster you see that we

are drawing a circle because our base

pointer is now managing a circle object

now because we are using dynamic binding

or late binding as some people call it

we can really do all kinds of crazy

things the first thing we can achieve is

set up one single method which is really

going to draw any kind of shape we throw

at it so let's do something like this

we're going to say void and we're going

to say draw shape and it is going to

take a shape pointer let's say s and the

only thing we're going to do in this

function and say s draw this is going to

call the draw method on whatever

parameter that we pass in here

and watch this if we go down here and

uncomment this section on drawing shapes

if we say draw and pass in a circle for

example or let's pass an oval and do

this one level and to do this level by

level we're going to pass in over one

and we should pass an address because

this is taking a pointer let's so let's

do this and if we build and run this

program let's see what happens here

we're going to build with gcc the world

is going to be good as you see here if

we clear and run rooster you see

and let's take out this thing using base

references here because this is just

going to confuse us we're going to build

again and i use gcc for this the build

is going to be good within clear and run

rooster you see oval drill because we

are passing in a novel object if we pass

in our shape let's say shape one for

example we're going to build the book is

going to be good as you see here if we

clear and run rooster we're going to see

shape draw if we pass in circle let's do

and the bold again we're going to build

with gcc we're going to clear and run

rooster you're going to see that circle

draw is called and this is really cool

we can only use a single method and this

method is going to take any shape we

throw at it and it is going to draw it

if we happen to be having 100 kinds of

shapes in our program we can just for

example loop through a collection

containing those shapes and if we call

the draw method on any shape we store in

our collection we're going to get the

correct shape drone and this is super

cool this is really powerful and i hope

you are excited to be able to achieve

this in c plus plus now we can also

achieve the same thing by using a method

that takes a reference for example so we

can say void joe shape let's say v1 and

we're going to pass a reference

we can say const and pass a reference

and say sr to say ship reference we can

do that and we're going to say sjo we're

going to call the jaw method on this

reference and let's see what happens if

we try this out let's say sr that's what

we should say here and this is going to

be taken by our visual studio code

editor if we go in here and change this

draw shape v1 we can pass in shape one

we can do that because this is taking a

if we build with gcc we are going to see

that the world is good we can clear

let's clear we're going to run the

rooster this is going to call shape draw

because we are using a reference to

manage a shaped object we can also pass

it over one and we're going to build

again and see how this works the bolt is

going to be good we can clear and run

rooster we're going to say overdraw and

we're going to see our information here

if we pass in our circle object

and the bolt we're going to pass this

through gcc the bolt is going to be good

we can clear and run rooster this is

going to draw a circle for us this is

really cool we have one method again

that is taking a parameter by reference

but we can use this method to draw any

kind of shape in our inheritance

hierarchy this is going to work really

well and it is doing dynamic binding

which is powered by virtual functions we

are using in our inheritance hierarchy

here you should really keep this in mind

now let's go back and see if we can even

use row pointers to do stuff i am going

to comment this out and i am going to

say roll pointers because i want you to

see something we're going to set up a

shape pointer we're going to say shape

do we have that on top here let's see if

yes we have shape ptr so let's say shape

and pass it a novel object we're going

to pass a novel again and we're going to

pass the address of 01 this is going to

do we can call the draw method and get

or get it called using dynamic binding

and say draw this is going to call the

correct version but one thing i want you

to see is that if a method is not

polymorphic or if a method is not

you want to get it called using

polymorphism for example if we go to our

oval class we're going to see that we

have a bunch of getters let's go in and

make them public so that they are

callable from the outside and if we try

polymorphically or using dynamic binding

that's not going to work let's do that

we're going to say get x rad and the

reason we might want to do something

like this is because we have this method

and it is set up on our oval class

so because we are using a base pointer

to manage a novel object some of you

might think uh-huh i might be able to

call this method because i am able to

call the job method which is also in the

public scope of our overclass but that's

not going to work because this method

dynamic binding or polymorphism is only

going to work if your methods are

virtual and they are set up across your

inheritance hierarchy so this is not

going to work if you try to do something

like this this is going to give you a

compiler error let's try and build and

see the compiler error and we're going

to see an error that says that no such

method on this object let's go here

class shape has no member name to get x

because the method is not virtual the

compiler is going to do static binding

and it is going to be using the type of

the pointer which is shaped to resolve

this method and it is going to see that

in shape we don't have a method called

get xrad and the compiler is going to

throw this compiler error here this is

what we get so this is not going to work

and i want you to be aware of this

another thing i want you to see

is that because we are using dynamic

we don't need we don't need to set up

all kinds of crazy collections to take

into account different shapes that we

have in our c plus plus program what

we're going to do here is use a base

pointer to manage the data that we store

in our array here so all i am going to

do is remove all this dirt here because

this is really dirt you don't want to do

something like that and we're going to

use a base pointer which is a shape

pointer and use that to set up an array

which can handle any kind of shape we

have in our inheritance hierarchy so we

can store it shape objects we can store

it over objects we can store in circle

objects and if we look like we do here

we're going to get the correct method

called and this is going to be super

cool so let's try and run this program

we're going to pass this through gcc why

do we have the red thing here let's

build and see if it goes away maybe this

is visual studio code having a problem

with our code the world is good so

visual studio code was playing with us

we're going to clear and run rooster

you're going to see that we're going to

be looping through this array here and

on the first iteration we're going to

call shape draw because the first thing

is the shape on the second iteration

we're going to call overdraw because the

second thing is a novel and we're going

hit the third iteration and call circle

draw because the third thing in this

collection is a circle hopefully you can

see that this is going to simplify our

programs a lot compared to what we were

in the last lecture and this is really

all i had to share in this lecture

showing you that you can achieve dynamic

binding or polymorphism or late binding

as some people call it using virtual

functions in your inheritance hierarchy

again all we had to do was mark our

member functions as a virtual and the

compiler is going to know that it can

set up dynamic polymorphism for your

types if you happen to be managing them

using a base pointer or a base reference

we are going to stop here in this

lecture and the next one we're going to

learn about slicing and the size of

go ahead and finish up here and meet me

there in this lecture we're going to

explore the size of polymorphic objects

or objects that use dynamic binding and

we're going to learn about the concept

of slicing if you happen to assign a

derived object to a base object we're

going to see how this works out in the

last two lectures we saw that we could

achieve static binding using a setup

like this we can set up an inheritance

hierarchy and we're going to have oval

derive or inherit from shape and we're

going to have circle inherit or derive

from over here and our methods are going

to be row they are not going to be

virtual on anything and this is going to

do static binding if you happen to

manage a derived object through a base

pointer or reference you want to get

dynamic holes you will get static

binding and the compiler will use the

base pointer or base reference to decide

which draw method to call on your object

we also saw that we could achieve

dynamic binding using virtual functions

and all we needed to do was mark our

methods as virtual in our inheritance

hierarchy here and this would give us

polymorphism or dynamic binding but one

thing you should know is that dynamic

binding is not free you're going to be

paying in terms of memory to get all

these cool things we saw in the last

lecture and we're going to be proving

that in this lecture what we're going to

be doing is basically set up our

inheritance hierarchy and we are going

to set that up in such a way that it is

going to be using static binding we're

going to see the sizes we get printed

out here and we're going to use dynamic

binding and compare the sizes and the

constitution is going to be that with

dynamic binding your objects are going

to be much larger because your simplest

plus program will need to keep track of

function calls dynamically and that

information is stored in what we call

virtual tables but i am not going to go

into that here because it is really out

of scope of a course like this but i

want you to be aware of this if you use

dynamic if you use dynamic binding your

objects are going to be much larger okay

the first thing i want to bring your

is object slicing and we're going to

look at a simple example here we have

our objects we have a shape object we

have an oval object and we have a circle

object and down here we want to assign

our circle object to a shape object

now notice that here we are not using a

pointer or a reference these are just

the row objects that we are assigning to

each other and what the competitor is

it's going to notice that a circle has a

shape according to it and it is going to

strip off the outer layers or in other

words it is going to strip off the

circle layer it is going to strip off

the oval layer and it is going to leave

in the shape part and that's what it is

going to assign to our shape object here

let's visualize this our shape class

looks like what we have here on the left

our oval class has a shape part into it

and our circle is going to have an over

part into it and that oval part is going

to have a shape part of it and this is

the setup that we have here now if we do

our assignment we're going to do

something like this the compiler is

going to see that we are already

to a shape and the compiler is going to

notice that what we have on the left is

just a shape and we don't have enough

space to store information about oval

and the circle here so what the compiler

is going to do it is going to strip off

all these things that we don't really

need and it is going to leave in only

shape part that we can assign on what we

have to the left so it is going to strip

off all these stands and we are going to

be left with something like this and

then what we have on the right is going

to be assigned on the left and we will

have our data stored in our ship to

object and if we try to use it that's

what you're going to get in memory so

this is referred to as slicing again the

compiler is going to notice that it

doesn't really have enough space on the

everything we have to the right of the

assignment here and it is going to strip

everything we don't need and it is only

going to leave in the shape part and

that's what it is going to assign on our

object that we have on the left of the

assignment operator here and this is

referred to as slicing in c plus plus

terminology i just want you to be aware

of this and we're going to see a lot of

this starting from now now that you know

this we're going to head over to visual

studio code and play with this a little

more here we are in our working folder

the current project is size of

polymorphic objects and slicing we are

going to grab the code from the last

lecture so let's grab everything except

for the binary file we are going to copy

everything and we're going to put that

in the current folder and we're going to

open this little guy in visual studio

code by dragging and dropping here this

is going to give us our project and we

can head over in the main cpp file

and clean up all the mess we got from

the last previous lectures we can also

take out these functions because i don't

and we are going to check out on our

classes notice that we are using dynamic

polymorphism because we have virtual

functions here so if we happen to be

using base pointers or base references

to manage our derived objects we will

get polymorphic results okay the first

thing we want to see is the size of

objects for our classes here because we

are using virtual functions let's head

over in the main cpp file and we're

going to put in a piece of code which is

just going to use the size of operator

of objects of these classes we can try

to build and run this program we're

going to use gcc here the world is just

going to be good we can bring up a

powershell window we can use to run

we're going to do that new terminal this

is going to bring us our window here we

can clear and run rooster we're going to

so you see that these are our sizes so

let's say that with uh dynamic is going

to be 40 for the base class with dynamic

portal morphism we're going to get 56

oval object and we're going to get

circle object here now we're going to

remove the setup that uses polymorphism

and we're going to see the results that

we get all we need to do is to remove

the virtual keyword here we can comment

it out you can do something like this in

shape and we're going to hop over in

oval and comment out the virtual key

world we can do something like this and

work without removing this completely

from our code because we still need to

leave this in as a reference we're going

to hop over to circle and do the same

and now that we have this setup we can

hop over to our main cpp file we're

going to see that we don't have any

squiggly lines of some kind so this is

going to be accepted by the compiler but

if we build and run this program we're

going to see different sizes let's see

if the world is good it is good as you

see here we can clear and run rooster

static binding the base object is 32

bytes the awful object is going to be 48

and hopefully you can see that with

dynamic polymorphism our objects are

going to be much larger because the

compiler has to keep track of the

information that allows it to

virtual function calls that's why our

objects are larger with polymorphism and

you should know that you are not getting

polymorphic results for free you are

going to be paying in terms of much more

memory that you use for your objects in

your c plus plus programs this is the

first thing i want you to see in this

lecture the second thing i want you to

be aware of is the concept of slicing

and this is going to happen if you

derived object and assign that to a row

based object let's do something like

that we are going to create a circle

object and then we're going to say shape

and say shape here and we're going to

this is something we could do

but notice that the compiler is not

giving us any kind of compiler error

because we can assign a circle to a

shape because a circle is really a shape

but from what we know in our inheritance

hierarchy a circle is really much more

than a row shape a circle has awful

information in it and it also has circle

information in it so it is really much

larger and much wider than a shape

object but the compiler is going to see

that we are trying to assign a circle to

a shape and it is going to be smart

that we don't really need oval and

circle information in our shape object

that we are storing here so the compiler

is going to slice off circle and oval

information and it is going to leave in

shape information and that's the only

thing we will be able to use with this

shape variable that we have in our c

plus plus program so if we say shape

drill you can try to guess what we are

going to get and let's go back and

re-enable polymorphism because some of

you might think we are going to get

with this setup here that's not what

we're going to get because we are not

going through bezel references or base

do what we are doing in this example on

slicing here so because we are not using

base references or base pointers in this

line here the compiler is going to see

that these are raw objects and it is

going to do slicing and slice of things

we don't need in our shape variable

that we are setting up on line 16 here

so if we call the draw method this is

it is not going to do dynamic

polymorphism here you should be aware of

this if you're not using the base

pointers or references and you hope to

get dynamic polymorphism results i hate

to break it to you but you're going to

be disappointed because the compiler is

going to slice off derived class

information and all you're going to be

left with is base class information here

that's why this is going to call ship

draw let's build and run and really make

you see this this is going to go through

gcc our favorite compiler the bullet is

going to be good we cannot clear and run

rooster you're going to see that it is

going to say shape draw even if we try

to assign a circle to a shape here this

is going to disappoint us because this

is really going to slice off circle and

and it is just going to leave in the

shape nucleus that we have in our circle

if i can say it like that this is really

all i had to share in this lecture i

hope you found it interesting we are

going to stop here in this lecture in

the next one we're going to see what

happens if we try to store polymorphic

go ahead and finish up here and meet me

there in this lecture we're going to

explore what happens if you try to

directly store polymorphic objects in a

in the last lecture we have seen that if

you assign a derived object to a base

the data from the derived object is

going to be basically sliced off if you

assign an oval to a shape the oval part

of the object is going to be sliced off

and we're going to be left with only

shaped data that we assigned to our

shape object we saw that this was

referred to as slicing in c plus plus

and the same is going to happen if you

assign a circle object to a shape the

circle information is going to be sliced

then the oval information is also going

to be sliced off and we're going to be

left with the inner shape part

that we assign to our shape object here

now i want you to see that this can

happen indirectly in ways that you might

not expect and we are going to use our

inheritance hierarchy again the base

class is going to be shape we're going

to inherit from that and get oval and

we're going to inherit from oval and get

so let's look at a piece of code here we

are creating a bunch of objects we have

a bunch of circles and ovals and we are

setting up an array that is going to

but what we are doing is storing our

pre created objects in our array here

and from what you already know if you

store objects in an array like this this

is going to create copies even if you

can't see that directly so what we have

in our array here is not dirt so what we

have in our array here is not any kind

of direct reference to the object we

have on top here these are just copies

and notice what is happening we are

in spots that are designed to store

direct shape objects and you might guess

what this is going to do this is going

circle and oval information and only

shape information is going to be stored

in this array here so if we happen to

look through this array like we do here

this is not going to call the most

specific drill method for circle or oval

this is just going to call the shape

version of our draw method here this is

something i want you to see okay some of

you might say what if i take my

shape information in here and assign

that to a pointer and then go through

that pointer to call the draw method

well i hate to break it to you but the

moment your data is sliced off in a

situation like this you'll never get

that data back so even if you try and

take the object and sign that to a

pointer or a reference you're never

going to get polymorphic data again the

data has been lost permanently and you

never get that so even if you try to go

through a pointer or a reference to

manage your object that we have in this

array if we call the draw method we want

to get polymorphic behavior we will get

to the shape version of our draw method

called so the data has been sliced off

permanently if we store our derived

objects in an array like this or even if

we directly assign a derived object to a

base object this is going to slice off

the data and we will never get it back

anyway you should really know this okay

anytime i try to explain this

students mostly come up with this

question what if i try to store

and do something like this now this is

not going to work and this is not even

go past the compilation stage of your

program the reason is we can't store

references in a collection and the

assignability rule you can't assign to a

reference and i changed the reference to

store somewhere else and it really drive

this home let's look at this example

here we have a variable called a it is

of entertype and we have a 56 value

inside and we set up a reference which

is going to be referencing the data we

have in a and down on this line here we

try to change the data in our reference

but this is not going to be changing

where this reference is pointing to or

where this reference is referencing this

will merely be changing the values in

our reference here and once we have this

reference we'll never be able to change

where it is pointing again so from this

hopefully you can understand that

references are not left assignable you

can't store thanks that are not left

because an array is designed to modify

the data of what is stored inside so if

we set up an array like this

the compiler thinks that at some later

point you will want to assign

other data to what is already stored in

this array and there is a hard

requirement on the data you store in

your collections for the type of that

data at least to be left assignable

and references are not left assignable

so we can't store them in a collection

like this if we're trying to do this

we're going to get a compiler error but

again some of you are going to say what

if we store in pointers well this is

going to work this is the basic working

going through base pointers to manage

derived objects this is going to use

polymorphism and here we will get the

so if our object is a circle we will

call the draw method on the circle

object if it is a novel we're going to

call the draw method for the over part

of our object here this is even going to

work if we go through smart pointers so

if we do something like this and store

in smart pointers and create our smart

pointers on the fly in our initializer

here this is going to work because

really a smart pointer is a wrapper on

top of the regular roll pointer in c

plus plus so again the message here is

that you need to be careful on what you

store in your collections if it is a raw

piece of ghana your data is going to be

sliced off if you store derived objects

in a collection that is designed to

base class data if you store any

references that's not even going to

compile but if you're storing any kind

of pointer row or smart this is going to

work because polymorphism was designed

in the first place to work with base

pointers that are managing derived

objects this is really cool and i want

you to be aware of this now that you

know this we're going to head over to

visual studio code and play with this a

little more here we are in our working

folder the current project is

polymorphic objects stored in

collections we are going to reuse the

code from the last lecture because we

need our inheritance hierarchy here and

this is going to serve us just well

and we are going to head over in our

current project and put in our code and

then we're going to open this in visual

studio code pretty quick let's do this

this is going to give us our code and we

have our shape class which is really

what we already know we have our oval

and we have our circle class take a good

look at this and what we want to see is

if we use different kinds of setups to

store objects of this inheritance

hierarchy in a collection like an array

let's go back to our main cpp file and

we are going to take out what we have in

here we're going to set up what we're

going to be using in this lecture we are

going to set up a bunch of objects that

we're going to be using here basically a

bunch of circles and ovals we can close

the left sidebar here and have some more

breathing room after this we're going to

set up an array which is going to store

copies of this object in this array here

which is called shapes one and after

this we're going to try and loop through

this array and try to do things with it

for example we can say for shape and we

may want to call the draw method on our

copy here so for example we can say s

and say draw going to see what happens

let's say references because we don't

range based for loop here so this is

going to avoid copies we do in this loop

and we're going to be directly

referencing whatever we have in this

now what do you expect to get we have

derived objects in this array

and with the setup we have here because

we are using virtual functions

polymorphic behavior so here we would

joe versions in circle and oval to be

called but that's not what is going to

happen we're going to see that we're

going to be calling shape versions of

our draw methods let's try and build and

show you this we're going to world with

gcc our favorite compiler the build is

going to go through we can kill this and

bring up a powershell window to allow us

to run our program we're going to say

rooster here and you're going to see

that we are drawing circle one over one

circle two over two circle three oval

three but we are calling the shape

and the reason is we are slicing off

derived class information in our objects

the moment we try to make a copy and

copy in a spot that is designed to store

objects of the base class so this is

basically what we saw in the last

on the slicing but it is disguised

because we are storing data in an array

and when you store data in an array like

this you're going to be making copies

and storing copies in your array and in

any copy you make you're going to be

basically slicing off oval and circle

information and only storing in shape

information for our objects here this is

what the compiler is going to do and

that really try and prove this we can

try and print the size of these objects

and see the sizes of these objects in

this array here when we loop so for

example we can say stdc out size of

circle one do we have circle one yes we

do so we're going to say size of circle

and we're going to put its size

information out here to be seen by

everybody we're going to say size of

circle one and we're going to print it

out and we are also going to print the

size of whatever iteration we are at in

our loop here that's the first thing

we're going to prep and we're going to

say size of object and we're going to

say size of s this is going to do

and we're going to loop and see if the

information we have on the outside is

the same as we have on the outside again

we are printing this information on the

which is really not yet in our array and

bring this in front of our array to make

this super clear and in our loop we are

printing information on a copy that we

have in our array because this is the

real deal we have in our array because

this is a reference hopefully this is

going to make sense and prove to you

that we are going to be working with

derived objects and the data is going to

be sliced off if we copy the data in our

array here this is what i want you to

see so we're going to run this again

we're going to pass this through gcc the

build is going to be good we're going to

now let's look at what we have here size

of circle 1 is 56 but you're going to

see that the size for all our objects in

has shrinked to 40 because derived class

information has been sliced off the

moment we copied our data in our array

here and this is what i want you to see

and i think we can even see this if we

go through our debugger for example we

and uh open our run tab and if we try to

run our program through the debugger the

build is going to be good and the binary

is going to be passed into our debugger

and we're going to hit our break point

in a minute so let's wait for this and

we have hit our break point here but

is look at our local variables on the

left let's look at our array the array

and if we go up we're going to see our

and we're going to see that we have five

indexes here because we have six

we can expand and see what we have at

index zero and you're going to see that

we just have description data because

this is a shape if we go back in our

class we're going to see that the only

thing we have in our shape class is

really a description member variable and

it is what we see in our array here just

description information because this is

a shaped object and we have lost or

derived class information and this is

really cool but if we go on top and for

example expand circle one we're going to

see that we have a novel part of us and

we have a ship part of us but these

events have been stripped off in our

array when we slice off the data from

derived objects to only store shape

information in our array here i hope

this makes sense now we're going to kill

our debugging session because we don't

need this anymore and we are going to

comment this out and see some other

comment with our data here we're going

to say if you store row derived objects

in an array which was set up to store

base class object the data is going to

be sliced off this is something i want

you to know but some of you are going to

what if we store it in references okay

so let's try and do that we're going to

set up a piece of code like this and

we're going to set up an array called

shapes2 and this array is going to be

basically storing references to the

objects we have on top here and we're

going to see what happens you notice

that we have a squiggly line already and

this is saying this is not going to work

because references can't really be

again as we saw in the slides the reason

references are not left assignable and

they can't be stored in a collection

like an array here the basic requirement

on the types that you can store in your

array is that they have to be left

assignable and our references are not

rest assignable so this is not going to

compile if we try to build our program

we're going to see that we're going to

and the build is going to finish with

errors and if we go up we're going to

see that declaration of shapes to us

array of references and this is not

allowed you can't have an array of

references in c plus plus and this is

the reason why so we're going to get a

compiler error here okay so now you know

this but some of you are going to say

what if we go through pointers well

polymorphism through virtual functions

was basically designed to work with base

pointers that are managing derived

objects and this is what we have here so

if we look we're going to be getting

polymorphic behavior and if we call our

draw method on our pointer here we're

going to get the most specific

joe method called and this is what we

want so we're going to try and weld this

again and show you that this is going to

work the build is going to be good we

and run rooster and we're going to see

that we are going to be looping around

and if we call the draw method we're

going to call the overdraw method circle

draw method overdraw method circle draw

method this is basically what we want

and we are going through base pointers

to really use polymorphism here this is

definitely going to work if you go

through smart pointers so let's comment

this out and set up another example to

really drive this home you can really

use any kind of smart pointer you can

use unique pointer or shared pointers so

here we will just be storing in shared

pointers because this is easier to

handle and we're going to head over to

the top and include the memory header if

you remember if you want to use smart

pointers in c plus plus you will have to

include the memory header which brings

in the data to set up smart pointers in

so this is going to look good now and if

we build we're going to get the most

specific version of our draw method

called through polymorphism that is

using virtual functions here so let's

build and show you that this is going to

work the book is going to be good we can

and run rooster and we are going to get

our versions of draw called the version

for a circle and the version for oval

because we are using base pointers to

manage derived objects here and our

class inheritance hierarchy is using

virtual functions for the draw method

here so this is going to work this is

really all i wanted you to see in this

lecture you should be careful if you try

derived objects in an array that was

designed to store base class data if you

are using raw data you're going to get

and you really need to be aware of this

because you want to have derived class

information if you try to store any

references this is not even going to

compile because references are not left

assignable but this is going to work if

you use role pointers or smart pointers

because polymorphism was basically

designed to work with base pointers or

references that are managing a derived

object which uses polymorphism we are

going to stop here in this lecture the

next one we're going to learn about the

override mechanism in c plus plus go

ahead and finish up here and meet me

there in this lecture we're going to

learn about the override specification

a kind of setup you can do to avoid

errors in your inheritance hierarchies

if you use virtual functions to set up

polymorphic behavior for your derived

objects and this is something that was

set up in ziplus plus to avoid easy to

for example if you have an inheritance

hierarchy like this you might be meaning

to set up a draw overrides for what we

have in the base class and an override

method that you have in your derived

class to really hide what we had in the

base class for example the draw method

novel is going to be overriding or

and the draw method in circle is going

to be overriding or hiding what we have

in oval this is the idea here but as you

set up your overrides you might make

mistakes for example you may mean to say

draw and i use a w that is in uppercase

and that's going to be bad because what

you will be putting in oval is going to

be a completely separate method that is

different from what we have on the top

and this is going to be really bad

you're not going to get polymorphic

behavior for the draw method in oval

because we are simply not overriding the

jaw method from shape and this is going

to be bad so in ziploc plus we can avoid

these problems by explicitly specifying

that the draw method we have in alpha is

an override and we can add this

specification after our method header

and the c plus plus compiler is going to

enforce that we are actually overriding

a method that exists in our parents

class which happens to be shape here if

we have no method called draw in the

base class we're going to get a compiler

error because we want to be basically

overriding any method here this is going

to protect us from problems if we make

typos in setting up our polymorphic

methods here this is the main thing we

can achieve with the override

specification now that you know this

we're going to head over to visual

studio code and play with us a little

more here we are in our working folder

the current project is override here

we're going to grab the code from the

last lecture because we are basically

going to be reusing the same code over

building on top of that if we need to do

that so we're going to put in our code

and we are going to open this in visual

studio code by dragging and dropping

here this is going to give us our code

and we can really do whatever we want

with that i think we can leave in the

code that is using the base pointer to

manage our derived objects i think this

well enough and we can take out

everything else because that's just

going to be confusion we don't need all

this here this is going to be serving us

well now we want to learn about the

and to learn about that we're going to

introduce a title on purpose here for

example suppose we want to set up a draw

an uppercase letter here for the w key

world i don't think this is really easy

to spot once you've made this mistake

and you're not going to be getting any

this is something valid you can set up a

completely new method and call it joe

and this is going to work but this will

be very hard to spot in your program and

the compiler won't protect you as we

just said if we build our program you're

going to see that it is going to bulk

just fine so let's pass this through gcc

the voltage is going to be good but we

want to get to the behavior that we want

i think we can take out this sddc out

statement inside our for loop here and

we can weld again this is going to be

less confusing okay so the build is good

we can bring up our powershell window

and i'm going to run rooster and see

what happens you're going to see that

for a circle we're going to draw a

we're going to be drawing shape so what

is happening here we are overriding our

joe method in the overclass so we should

get polymorphic behavior because this is

a virtual function and it is called draw

exactly the same thing like we had in

the base class except we've made a

really simple typo here but it is really

hard to track and get hold of we have

named our method draw but the w is in

uppercase so this is a completely

different method than the draw method we

originally intended to override in our

base class and this is really hard to

follow and keep track of we can protect

ourselves by adding the override

specification so if we say override the

compiler is going to help out and make

sure that we are actually trying to

override the method that exists in the

shape class and if it doesn't exist

we're going to get a compiler error then

we're going to look at this and really

spot this mistake here this is what you

can achieve with the override keyword

and in fact i do recommend and advise

you to use this in your inheritance

hierarchy if you happen to be using

this is going to save you a lot of time

if you make mistakes like this so we're

going to try and run this and show you

the compiler error we get so let's do

that we're going to pass this through

fail as we see here and we're going to

get a compiler saying errol virtual void

overall joe cost marked override but

does not override this is super clear we

are saying we want to override here but

we're not overriding any method called

joe with an uppercase because we don't

have that in shape here this is the

message once we see the problem we can

correct it we're going to use in

lowercase letter for w and this is going

to work just fine now we're going to use

the same mechanism to protect ourselves

from ourselves in circle class so we're

going to override our draw method but

we're going to say that we want to

override explicitly and if we're both

now let's pass this through gcc this is

going to build successfully and if we

run our program we're going to get

polymorphic behavior let's do that you

see that circle draw overdraw circle

draw overdraw this is what we expect

this is really cool this is really all i

had to share in this lecture i hope you

found it interesting use the override

keyword in your inheritance hierarchy

because that's going to protect you from

easy to make typos that are really going

to give you a hard time otherwise we are

going to stop here in this lecture in

the next one we're going to explore the

concepts of overriding and hiding in

go ahead and finish up here and meet me

there in this lecture we're going to

zoom in on overloading overriding and

hiding we have seen that overriding is a

mechanism we have in c plus plus to be

most specific versions of our virtual

methods in derived classes so for

example the draw method we have in oval

is overriding or eclipsing the one we

have in shape and the draw method in

or hiding or eclipsing the one we have

in awful this is the concept here but

what happens if we introduce the concept

of overloading and mix that up with

overriding as we have seen so far so

suppose we do something like this this

is our shape class it is going to have

two versions of the draw method we have

one that takes one parameter for example

this could be the color that we want to

draw our shape with and another one is

not going to take any parameter and

these are two overloads of our virtual

method here so what is going to happen

in our derived classes that are going to

inherit this virtual method so let's

look at an example here we have a simple

example that is setting up objects of

our shapes we have a shape object we

have a novel object and we have a circle

object here if we call the draw method

on our most derived class which is

circle we're going to see that this is

going to work we can draw without a

parameter and we can draw with one

parameter which is going to be our color

depth this is going to work just fine we

our inherited method from the shape

class and this is really cool but what

happens if you override this method in

our overclass suppose we hijack the

inheritance process and set up another

draw method in our overclass and we only

override the overload that doesn't take

any parameter we can do something like

this but the moment you do this this is

going to only override this method and

it is going to hide all the other draw

methods that we had in our base class

which is shaped here and this is

something i want you to know so once you

override a single overload of your

all the other overloads are going to be

hidden and they won't be usable anymore

by downstream inheritance classes if you

want all the overloads to be available

classes you have no choice but to

explicitly override each of them and

that's how it's going to work so if we

look at the example here we're going to

see that the draw call without a

parameter is going to work because this

is overridden in our oval class but if

we call the one which takes a parameter

this is going to be hidden at the oval

level and we want to have access to that

in circle and if we try to call this

we're going to get a compiler error

again the message is if you override one

overload of your virtual functions in

the base class all the other ones are

going to be hidden and you have no

choice but to explicitly override them

for them to be available and usable in

downstream classes this is the message i

wanted to convey here okay so now we

know this but what if we set up another

downstream for example what if we go in

our oval class and set up another

overload which is going to have two

parameters for example we might have the

color depth and the color here that we

want to draw with okay so one thing you

should know is that this this method is

not going to participate in shape

polymorphism and what i mean is that if

we go through a base pointer or

reference to manage derived objects we

can't really call this method with shape

polymorphism so if we go through our

shape pointer or reference we want to be

really able to call this method if we

try to call it we will get a compiler

error the reason is this method is not

to the shape class that's why it's not

going to participate in shape

polymorphism the only methods that are

going to participate in shape

polymorphism are the methods that are

declared in the base class and they are

virtual this is the condition here and

if you violate this condition in any way

shape polymorphism or base class

polymorphism in this case is not going

to work and you will get a compiler

error so if you try to do something like

this and you want to call your draw

method with two parameters you're going

to get a bunch of compiler errors and

this is not going to work another thing

i want you to see is that if you assign

a derived object to a base object

your derived virtual functions are going

to be wiped out as part of the slicing

that we have learned about already so

the circle port is going to be wiped out

the oval part is going to be sliced off

and the draw method is going to go with

our oval part and we will only be left

with the shareport and if we try to call

this method here we will get a compiler

error because it's no longer available

it's been sliced off this is really what

i want you to see here now that we know

this we're going to head over to visual

studio code and play with this a little

more here we are in our working folder

the current project is overloading

overriding and hiding we want to explore

these concepts in a little more detail

we're going to grab the code from the

last lecture because that's going to be

a good starting point we're going to

take out the binary we don't want that

and we're going to copy and we're going

to put that in our current project here

this is going to do and we are going to

open this in visual studio code pretty

quick by dragging and dropping here and

we're going to see that we have a bunch

virtual functions here who just have the

draw version but we can set up an

overload of this draw method here this

is what we want to do so i am going to

go below here and set up an overload of

this method this is going to be taking

the color depth as a parameter and we

want to see how usable this is

downstream so we're going to go down in

and take out what we don't need here we

really need a bunch of objects we can

set up circle one and over one and we

will see that we can call this method

we're going to say circle one draw

without a parameter and we're going to

say circle one draw and pass and 44 as

our parameter and let's go back and make

sure that we have our overload and this

is going to be taking the color depth

and let's try and build our program

because we have a squiggly line here

let's see if it is just a visual studio

code playing games with us we're going

to pass this through gcc and we will

have a compiler error here so what is

going on candidate virtual draw cost

let's go up and see what kind of problem

we have here ah this is the concept we

just talked about in the slides we are

setting up our overloads here but this

is being eclipsed by the overloads that

we are setting up in oval you see we

have a draw override and this is also

being eclipsed by the override we have

in our circle class here if we want the

two overloads we have from shape to be

available we can comment out the

overrides we have both in circle and

oval let's do that and that's going to

be available and usable so let's do that

this is a really good learning

opportunity and now if we go in main cpp

we're going to see that this is going to

become available so we can upload this

with gcc again to bring visual studio

code up to date and you see the build is

good and our methods are usable even

from derived classes so for example we

can also set up a novel object let's say

oval one and say draw this is going to

work if we say ovo one draw and pass in

a parameter let's put in 54 for example

this is going to do you're going to see

that this is going to be accepted by

visual studio code and if we weld and

run this program it is going to build it

is going to be calling the inherited

circle here the boat is good we can kill

our terminal here and bring up a

powershell window we can use to run our

program we're going to see that we call

shape draw and shape draw because these

the shape class that's why we are saying

shape draw here and we're going to be

drawing a oval and a drawing with a

color depth we're going to be drawing

the circle and drawing with the color

depth here this is the message i want to

convey but the moment we override these

methods in any downstream class for

example if we go in our over class and

and comment out the override for the

draw method notice that we are just

overriding a single overload again if we

go back to our shape class we have an

overload that doesn't take any parameter

we also have an overload which is going

to take one parameter in oval we are

just going to override the overload that

doesn't take any parameter but this is

going to hide all the other overloads we

had for the draw method here and this is

the only overload that is going to be

in downstream classes so if we go back

in main we're going to see that the one

with a parameter is not going to work

and we're going to get a bunch of

compiler errors this is going to be the

uncomment this guy the others are going

to be eclipsed again the other one we

have is just the one with one parameter

but this is going to stay true even if

you have a hundred overloads all the

others are not going to be available if

you happen to only override one of the

the other overloads are going to be

hidden by this one overall ride that you

are putting in your inheritance

hierarchy you should really know this if

you want this guide to be available in

downstream classes for example you can

also override that in derived classes

this is an option we can go in oval and

put in another overload for this this is

going to bring this back in scope so we

can say overdraw here with the color

depth i don't think we copied the right

thing we can grab this and go in oval

and put this in place this is going to

do we're going to say oval drawing and

we can go in circle and also put this

end this is an option and we're going to

say circle drawing and now you see that

the squiggly lines in main go away

because we have overridden all the

overloads okay if we build and run our

program we're going to see that this is

going to work as we expect the world is

going to be good and we can clear

and run rooster we're going to see that

overdraw called overdraw called we are

calling our derived overrides and this

is really cool this is what we want here

let's take this back because we don't

overridden in our inherited classes so

we're going to take this out in oval

and we're going to take this out in

circle and i want you to see that shaped

polymorphism is not going to work if you

override your methods at a downstream

level so what we are going to do we are

going to go at the oval level and set up

another overload for the joe method here

but this draw method is not going to

participate in shape polymorphism

because it is really declared at the

oval level and any base pointer we have

or any shape pointer we have is not

going to have any knowledge of this

overload that we are about to set up

here this is what i want you to know

okay so we are going to go in our oval

class and set up that overload we can

set that up here it is going to be taken

two parameters one is going to be the

color depth the other is going to be the

color and we don't want to pass a string

by a value like this we can use std

string view and we can include that if

we need to but it looks like visual

studio code has got this from something

else we have included before but we can

include that explicitly to avoid

problems so let's do that we're going to

say stream view here and now we want to

see that this method is not going to

participate in shape polymorphism even

if it is a virtual functions the reason

is this is not going to be known by your

shape pointers because it is not

declared at the sherpa level here i

really want you to know this we're going

to take out everything we had here and

we can set up a shape pointer we're

going to say shape and say ship ptr and

we're going to set up a derived object

here we can say new and serious circle

and what do we need to build the circle

object we need the radius and the

description so we're going to put that

in place here the radius is going to be

something like 10 why not and the

description is going to be circle one

how creative and we want to see if our

method is available through polymorphism

and it is not going to be available

because the method was not declared at

the shape level so if we do shape ptr

and say draw and we have a method which

is going to take two parameters at the

oval level we have the color depth and

so for example if we go in main and say

not let's say this is something that

45 because this is an integer parameter

and we're going to pass in a string

let's say red you're going to see that

this is not going to compile

because the draw method with two

parameters is not known at the shape

level this is the message i want to

convey here so if you want your method

to be usable with polymorphism the

method has to show up at the top level

this is what i want you to see here if

we're trying to build this we're going

to get a compiler error and you need to

be aware of this but know that even if

this is not working with shape

polymorphism this can work with oval

polymorphism and this is an idea i am

going to explore in the next lecture

where we learn about the fact that polar

morphism can be set up at different

levels so we are going to stop here in

this lecture and explore that idea in

detail in the next lecture so go ahead

and finish up here and meet me there in

this lecture we're going to explore the

polymorphism at different levels in our

suppose we have a hierarchy like we see

here the top level class is animal and

we can derive from animal and create a

feline animal we can derive from feline

and create a dog animal we can derive

from feline create a cat animal we can

also do it the other way and create a

bird which is also an animal a bird is

going to have its own methods and member

variables that make it a bird we can

derive from a bird create a pigeon and

we can derive from a bird and create a

and we can do all these things that

so the idea i want to expose here is

doesn't have to always only work on the

top level class if you have an

inheritance hierarchy like this if you

want you can declare a virtual method at

the feline level and make sure that

method is also available in deriving

class and you can set up feline

polymorphism if that makes sense for

your application following the same idea

you can also set up a virtual method in

the bird class and you can have that

method overridden in downstream

inheritance classes like pigeon and crow

and you can set up bird polymorphism in

your c plus plus program if that makes

sense of course you can still use animal

polymorphism if you want to do that and

that's going to work as well this is the

idea we're going to explore here okay so

with that inheritance hierarchy in mind

we can create animal polymorphism and

animal polymorphism is just going

through the animal base pointer and

using that to manage derived objects for

example here we have a dog we have a cat

we have a pigeon we have a crow we can

do animal polymorphism and storing any

kind of animal we have here you see we

are putting in a dog we are putting in a

cat we are putting in a pigeon and we

and if we do animal polymorphism and

call the breathe method which exists in

any kind of animal we have in our

program this is going to call the most

specific breathe method on each animal

and this is going to work really well

this is going to do animal polymorphism

following the same idea we can also do

feline polymorphism and in this case

feline is going to be acting as our base

pointer so again we have our dog we have

our cat we have our pigeon if we do

feline polymorphism we will have to put

in all kinds of crazy felines we have in

our program for example we can put in

dog and cat and this is going to work if

you do fill out a polymorphism like we

are doing here and put in an animal this

is not going to work because the animal

top level class is probably not going to

virtual method we are interested in here

for example here we are calling the run

method and the run method is not set up

at the animal level let's go back and

look at our inheritance hierarchy here

you see this is our animal class our

virtual method is going to be breathed

because any kind of animal we have is

going to need to breathe but the run

method is set up at the feline level so

if we try and store an an animal in a

setup that uses filing polymorphism the

run method is not going to be available

and we're going to get a compiler error

so i want you to know this but we will

also see this in a minute when we hit

visual studio code to really play with

us okay we can also do bird polymorphism

and here you see we have two objects one

is a pigeon the other is a crow

and we're going to do bird polymorphism

here and what that means is that we will

use a bird pointer to manage all kinds

of crazy birds in our c plus plus

program for example we can use that to

manage a pigeon we can use that to

manage a crow and if we loop through our

birds and call the fly method the most

specific fly method is going to be

called in this case at the first

iteration we're going to call the fly

method on our pigeon object at the

second iteration we're going to call the

fly method on our crawl object here and

this is going to work now that you know

this we're going to head over to visual

studio code and play with this a little

more here we are in our working folder

the current project is polymorphism at

different levels we're going to grab our

template files let's grab it all we're

going to copy this and put this in our

and we're going to open this little guy

in visual studio code like we always do

and before we open this up i am going to

put in the classes i have lying around

on my drive and these are going to be

the classes making up our inheritance

hierarchy here to make things go faster

if you want you can grab these classes

from the attached resource section on

this lecture you're going to find all

these files you can download them and

put them in your project and use that as

a starting point because you don't

really want to be creating all these

classes this is going to just waste your

time the basic idea i wanted to expose

here is doing polymorphism at different

levels so we're going to open this up in

visual studio code by dragging and

dropping here this is going to give us

our good starting point you see we have

a bunch of classes in here but all these

classes are really trying to set up the

inheritance hierarchy we have here the

top class is going to be the animal

we can derive from animal and create a

and we can derive from animal and also

create a bird class we can derive from

feline and create a dark we can derive

from feline and create a cat

and we can also derive from bird create

a pigeon we can also derive from bird

and create a crowd class and at each

level we're going to have a virtual

that other deriving classes can call

through polymorphism for example if we

do animal polymorphism we will get the

correct breathe method called regardless

of the actual object we are managing

if we do feline polymorphism we can

manage our objects through feline

pointers but we will get the correct run

method called regardless of which kind

of object we are calling this method on

so if we call the run method on a base

pointer managing a dog object we will

get the run method called on the dog

object this is what we mean here okay so

we have our classes here let's take a

closer look at our animal class it is

our top level class and it is going to

have a virtual method which is called

breathe it is caused because it is not

modifying our class here notice that we

don't have a virtual destructor because

i wanted to keep this simple but in your

practical object you should make your

destructors virtual if you happen to

have a virtual function in your class

here so for example we can even do that

let's make this virtual this is not

this is going to be our top class we

cannot look at the implementation file

it is not going to do anything special

it is just going to forward whatever

parameter we pass and use that to

initialize our member variable i think

we can also go in and change our

parameter to a string view so we can do

that hdd string view let's go in the cpp

file and also change that pretty quick

we're going to say std string view here

and this is our animal class we're going

to go in our feline class because that's

feline is going to be inheriting from

animal publicly just as we see here

we're not going to really do anything

special we're going to set up a member

and we're going to forward the data from

our constructor and use that to

initialize stuff in our class here our

parameters are also going to be passed

as std string view types so let's do

that here and this is in place we also

have a virtual method which is called

run and inside we are just printing

which kind of object we have

and uh giving a hint on the method that

is being called here this is what we

just do here and we don't intend to

create feline objects directly that's

why we're not setting up any overrides

of the top that's why we are not setting

overrides for these methods but we will

do that in downstream classes for

example dog and cat because that's going

to make sense there let's go in the cpp

file for feline and also change things a

little bit we're going to use std string

view parameters let's do that for the

second parameter as well and this is our

filling class so we can go in and look

at our dog class let's see if we can

find it and i don't think we made our

destructor in feline a virtual so let's

do that and look at our delta class

pretty quick here we have our dog it's

going to have no member variable at all

and it will just forward this data to

upstream classes but we can override our

breathe method we get from the animal

class we can do that and we are going to

say we can grab this entire thing and

we're going to go in dark we can do that

if we want we're going to put this

method down below here and we're going

to say breathe we're going to say that

this is overriding what we have on top

and we're going to say dog breathe

called this is going to do and we also

need to change our parameters to hdd

strength view let's do that this is

going to make things work better because

we will avoid unnecessary copies and we

will be able to pass string literals as

parameters to this constructor here this

is what we want to achieve with us we

can hit the cpp file for a dog class and

change the parameters again std string

view and we're going to say std string

view as well here and we're going to go

to the header file again and make sure

we have a virtual destructor here

because this is good practice if you are

using virtual functions like we are

doing here we can grab our breathe

method and hop over to our cat class

again remember the inheritance hierarchy

we are going after is what we have here

so if you are confused please come back

and look at this you're going to really

understand what we are doing here we're

going to go to the dog class and make

sure it is working as we want so we just

did the dog class and we just made sure

it works like we want now we're going to

hop over to cat and make sure it is now

we're going to hop over to the cat class

and make sure it is overriding the brief

method to make sure the correct method

is called okay so let's do that we're

going to hop over to our cat class it is

have its own meow method but it can also

override the breathe method we get from

the animal class so let's do that we can

and we can go to our cat class let's do

that we're going to put in our virtual

method and we're going to say cat

breathe and this is really all we also

need to set up our parameters correctly

using std string view let's do this std

string view and this is really all we

need to do here we can also make our

destructor virtual because this is good

practice we hop over in the cpp file and

change our parameters to be of type std

string view let's do this and this is

done we can really work with this

inheritance hierarchy here we're going

to also go pretty fast and work on the

other side of our inheritance hierarchy

we're going to work on birds let's look

at the bird class it is going to inherit

from animal it is not going to do

anything special really but we just want

to change the type of our parameters to

std string view and i'm going to do that

on the second parameter and we are going

to hop over in the cpp file and change

these things here let's do that we're

going to say std string view and do the

same thing here std string view and bird

is done we can grab our breathe method

for example let's go back to the top and

grab that from our animal class and

we're going to hop over to one kind of

bird we have in our program we can look

pigeon for example the last class here

we're going to override the breathe

method and i'm going to say pigeon

breathe and we are going to change the

type of our parameters here to std

string view and i'm going to do the same

here and let's hop over to the cpp file

and change the type of our parameter

let's do that for the second parameter

here this is done let's look at the

second kind of bird we have i think we

have the crow class we also want to

override the breathe method we're going

to say crow breathe and we can go up and

change our parameter to be of type std

string view and we're going to do that

here again if you are not interested in

these changes you can just grab the code

and you're going to have all these

classes ready for use i just wanted to

correct this little problem i had in my

classes on my drive because this is not

good to design in modern c plus plus we

wanted to do things proper because we

are really learning about modern c plus

plus here let's hop over to the cpp file

and finish this up we're going to change

the type to hdd stream view and uh let's

use view correctly and we're going to

say std string view on the second

parameter and this is done now we have

our inheritance hierarchy and we're

going to start by looking at animal

polymorphism again we just set up this

inheritance hierarchy now we are going

to try and do animal polymorphism okay

so now we're going to hop over to the

main cpp file and we are going to clean

it up a little bit remove whatever it is

we don't need we are going to put in our

includes we're going to include all of

the fans in our file here animal feline

dog cat bird pigeon and crow we're going

to include all this and we just want to

play with animal polymorphism here we

are going to set up a bunch of objects

and we're going to put in dog cat pigeon

and crow all kinds of crazy animals we

can create in our c plus plus program

and we're going to put them in an array

that is storing animal pointer and this

enable polymorphism for our objects that

we have in here remember animal sets up

a virtual method called draw if we go

back we're going to find that and we

made sure to override this method in all

kinds of crazy animals we can create for

example in our cat we have a breathe

method overridden in our dog class we

have the breathe method overridden and

what we want to achieve in our main cpp

file let's go there if i can find it we

want to achieve a setup so that if we

call the breathe method we're going to

call the most specific breathe method on

our animal pointer here even if we are

calling that method on a base pointer

this is what we want to achieve this is

going to be animal polymorphism because

the base pointer is of animal type this

is what we mean here let's try and build

this program so if we look and call the

breathe method the correct breathe

method is going to be called and what we

expect for the first object which is a

dark object we're going to get the dark

breathe method called for the second

iteration the category breathe method is

going to be called for the third

for the third iteration the pigeon

breath method is going to be called for

crow breathe method is going to be

called this is what we expect to see

if we run this program here so let's do

this we're going to pass this through

gcc our favorite compiler we can use any

compiler we want but gcc is going to do

in this case okay the build is good we

can bring up a powershell window to play

with and we're going to run rooster our

program and if we run this you're going

to see that in our loop the first

iteration is going to call dog breathe

because the first object is a dog the

second iteration is going to call cat

breathe because the second object is a

the third iteration is going to call

pigeon breathe because the third object

is a pigeon and the last iteration is

going to call crow breathe because the

last object is a crow and notice that we

are calling the breathe method through a

base animal pointer and this is what

polymorphism is all about and what we

are doing here is animal polymorphism

but this is not what we are really after

in this lecture we want to see that we

bird polymorphism in our inheritance

hierarchy so we're going to put in a

separator let's do sddc out and put in a

bunch of dashes here or hyphens some

people call them like that doesn't

really matter and we're going to play

with feline polymorphism let's do this

we are going to go down and put in a

simple piece of coat that we're going to

be using to play with things here and

we're going to set up a bunch of objects

we have a dog we have a cat we have a

pigeon and we are going to use a feline

pointer to manage feline derived objects

for example we're going to use this

pointer to manage a dog and a cat but

one thing i want you to see is that if

you put in a pigeon for example this is

not going to work because a pigeon is

not a feline so the compiler is going to

give you a compiler error let's try and

do that we're going to try and put in

pigeon here pigeon 2 you can select this

and if we do that you're going to see

that we get a squeaky line this is the

sign that this is going to go wrong

we are storing in felines and the pigeon

is really not a feline even by our

inheritance hierarchy so the compiler is

going to give us a compiler error let's

try and weld to show you the compiler

error okay the world finished with

errors and if we go and we're going to

find that cannot convert pigeon to feed

line pointer so this is the error here

you can't do something like this even if

you create an animal object let's say

that we're going to go in and create

animal and we're going to say animal one

we can do that and we're going to pass

in the description i think we can do

that we can do something like this and

if we try and pass in the address of

animal one let's do that this is also

going to give us a compiler error

because animal is not a feline again if

you get confused come back and look at

our inheritance hierarchy here

what we are setting up in our code we

are using feline polymorphism but we

want to store an animal in a raid that

is storing felines and this is going to

be a problem because the compiler isn't

really going to be able to process this

our base pointer is a feline and we

should really be able to only store in

derived types from feline but we are

putting in a superclass or a parent

which will not be able to have these

specializations that feline is doing so

the compiler is really saying this is

crazy i can't do this i am going to

throw a compiler error this is the

behavior we get here okay so this is

going to give us a compiler error and

let's run and see that we're going to

use gcc the book is going to finish with

an error and we are going to see that we

have an invalid conversion from animal

pointer to filament pointer this is what

we want to do here we want to convert an

animal pointer and store that in a slot

that is only supposed to store feline

pointers so this is not going to work

but if you do everything right and only

derived types of feline you're going to

get the correct length to work and let's

look at our dog class let's open it

again we're going to look at dog and

we're going to have a run method but we

don't have that set up for our dog class

but we can do that pretty quick let's

look at cat and see if we have a run

method we don't but we can set that up

let's go to feline and copy our virtual

and we are going to go in dog

and set up another virtual method which

run and this is going to be an override

of what we have in our inheritance

hierarchy so this is an override method

we are also going to do the same but

before we go let's say that this is the

dog class we are doing thanks from

we are going to grab this method again

and go in cat because that's another

feline we have in our program we can do

something like this and we're going to

okay so now let's come back to maine

and we're going to weld again we're

going to pass this through gcc and we

still have a pigeon in here so this is

not good let's check this out

make sure that we only have a few lines

in this array here let's build again

okay you see the bolt is good

and run rooster we're going to have our

separator here and you're going to see

that we are calling our dog method at

the first iteration because the first

object is a dog and we are calling a cat

running method because the second object

is a cat and this is filing polymorphism

in action hopefully this proves to you

that we can do polymorphism at different

levels depending on what we want to

achieve in our c plus plus program to

close off this lecture we are also going

to set up bird polymorphism let's do

that we're going to put in a separator

and we're going to say vertical demod

present and we are going to put in a

bunch of objects and set up a base

array which is going to be a bird

pointer array in this case and we're

going to be storing in derived objects

of the base pointer type so we are going

to be storing any derived objects of

bird and we have a pigeon and a crow and

this is the setup we want here now let's

go and look at the setup we have in our

pigeon for example we don't have a fly

method we just have a cool method

if we go in our crow we're going to see

fly method we're just having the cow

method because the crowd calls

but if we call our fly method because we

don't have this method overridden in any

version of the fly method called so we

called i want you to see this let's hop

over to the main cpp file and make sure

we have the correct setup looks like

this is what we want we're going to

build this with gcc the book is going to

be good as we see here and we're going

to run now we're going to see bird fly

bird fly for pigeon one and crow one

but this is not using any derived method

and a pigeon class if you want you can

fly method and you're going to get that

called let's actually do that because

i'd like to show you things directly so

that you can really see with your own

eyes so we're going to go in bird and

grab the fly method and we're going to

override this in pigeon we can do that

and we're going to override here and we

are going to say pigeon here and we can

grab this and i put this method also in

the crowd class can do that and we're

going to say crow here now if we run

using what we have in the main cpp file

for the first iteration we're going to

call the fly method on the pigeon object

because we have the fly method

overwritten at the pigeon level

as we see here this is right here

beneath our eyes and we're going to see

this in action if we run this program

here the same is going to happen for the

crow object here let's build with gcc to

really prove this the builder is going

to go through we can clear and run

rooster and we're going to see pigeon

fly crowd fly this is proving what we

set up in this lecture here this is

really all i had to share i hope you

found this interesting the main message

is that you can set up polymorphism at

different levels in your inheritance

hierarchy depending on what you want to

achieve in your c plus plus program we

saw that we could do the usual thing and

as the driver for our polymorphism and

we did animal polymorphism here but

nothing prevents you from doing feline

polymorphism or bird polymorphism as we

saw in this lecture we are going to stop

here in this one in the next one we're

going to see how we can do polymorphism

go ahead and finish up here and make me

there in this lecture we're going to

explore how inheritance and polymorphism

play out with static members that we

have in our classes and we're going to

be using this inheritance hierarchy here

our base class is going to be shape

we're going to inherit from that and

create an ellipse class let's look at

some code here so we're going to set up

our base class as shape as we said and

we're going to have one member variable

which is going to be our description

here we're going to have a constructor

and we're going to have a default

constructor which is really not

important here but notice that we have a

static member which is called m count

and if you remember a static member

is a kind of variable which is

associated with the type itself it's not

associated with any object that you

create if you forgot this please go back

to our chapter on classes or user

defined types you're going to learn all

about static variables here we are just

exploring how they play out with

inheritance and polymorphism now we have

a shape class if we inherit from it and

create an ellipse class for example

we're going to have all the data that

was public in our base class to be

public in this class as well so by that

logic we are also going to get this

static variable inherited and we're

going to be able to access it from

ellipse objects let's try and use this

in code here to really drive the point

home here we are creating a batch of

shape objects here is our first shape we

print our static variable through this

syntax here because it is public we can

do this we're going to get a one because

we just have one shape here we create a

second shape and we print the count

we're going to get two because we just

have two shapes in here we create our

third shape and we try and print the

count we're going to get three and if

you wonder how we are incrementing this

static variable we may do this in our

constructor we're going to see how this

works exactly once we hit visual studio

code in a minute but note that every

time we create an object we're going to

be incrementing our static variable

that's why we see one two three as we

created these objects here this is the

logic now we have three shapes here we

go down and create a new object which is

of ellipse type if we print the shape

count we're going to get four because an

ellipse is a shape and ellipse is

inheriting the static variable from

shape so we're going to get a 4 printed

out here but if we also print ellipse

count we're going to get a 4

even if we really just have one ellipse

so the static variable from shape is

being inherited and used in our ellipse

the problem here is that the static

variable we are using in shape and

ellipse are the same because the one we

have in ellipse was inherited from shape

that's why we have these results here

but sometimes we just want to have

ellipse count to b1 here because in

reality we really have one ellipse so

how do we do that to get that behavior

you can also set up another static

variable named exactly the same way at

the ellipse level and you can do that

like this you can also override the gate

count method to return the current count

in ellipse this is going to work through

polymorphism because the getcount method

if you call this method through a

basepointer you will get the correct one

called which is going to be the most

specific one through polymorphism but

what we want to see is how

things are going to work now that we

have a static variable which is named

exactly the same as the one we have in

our base class here the one in shape is

exactly named m count it is a static

variable of type and the one we have in

ellipse is also the same it is a static

variable called m count of type and but

ellipse is going to maintain its own

static variable and shape is going to

maintain its own static variable now we

are going to get this kind of behavior

we are going to see that if we try and

print the count of shapes we have we're

going to get a four here but now if we

try and print the count from ellipse

we're going to get a one because we

already have one ellipse and this is

working because ellipse is going to

static variable and this is going to

give you this behavior if it is what we

are after in our c plus plus program now

we can also go on and create a bunch of

other objects here we are going to store

them in this array which is going to be

storing shared pointers to shape

and we're going to store in derived

objects this is the syntax we can use to

do this and at the moment we do this

we're going to get six shapes because

in total we already have six shapes but

three of those shapes are going to be

ellipses and if we try to print the

ellipse count we're going to see that we

have three ellipses in our c plus plus

program and this is going to do

what we want another thing you could do

is also do shape polymorphism and call

the gatecount method and you're going to

get the correct getcount method and

print the most specific account if we

are calling that method on an ellipse

object for example we're going to print

three if we call that on a shape object

we're going to get sex and that's the

behavior we could achieve with

polymorphism with static member

variables and i really want you to be

aware of this now that you know this

we're going to head over to visual

studio code and play with us a little

more here we are in our working folder

the current project is inheritance and

polymorphism with static members we're

going to grab our template files and put

them in place and i am going to grab our

classes from my drive and use this as

the starting point again if you don't

want to type or create these classes you

can use the files provided in the

resource section of this lecture you can

download them and use them directly

without having to create them because we

are really interested in how static

members behave with our inheritance

hierarchy which happens to be setting up

polymorphism this is what we want to

learn about here i am going to open this

up in visual studio code and we're going

to take a good look at our classes the

base class is going to be shape which is

what we have here it's going to have a

virtual method which is get count here

and we have a static member which is of

i am going to change my parameter here

because that's what we should do in

modern c plus plus let's look at the cpp

file for this and we're going to fix

this a little bit and we're going to hop

over back to the header file and look at

what we have we have a virtual method

which is going to return this count here

it is a const method because it's really

not going to modify it's just going to

return a copy of the count member

and this is a static member variable

notice that it is not in line so we will

need to define this in the cpp file

somewhere because this is a declaration

we need to put in a definition which is

what we have in our cpp file here

because we are doing thanks in the older

c plus plus way we are going to

increment our account member variable in

our constructor and this is going to

achieve the behavior we really want to

have the m count member variable which

is static incremented each time we'll

create a shape object here let's go back

and look at our destructor and make sure

that it is virtual because we have

virtual functions in this class and this

is the setup we have let's look at

ellipse and we're going to take out this

static member variable because

we don't want to set it up as of now we

will enable it in a minute let's make

let's remove this because i don't want

this and now we can try to create

objects of our classes and see how these

guys play out we can also go in ellipse

and make sure the constructor is taken

std string views where we are needing

strings you can do that and hop over to

the cpp file and do that std string view

i think this is going to make a visual

we can hop over to the main cpp file and

clean it up a little bit and we are

include ellipse and in our main function

we're going to create a bunch of objects

let's close the left sidebar here

because we don't really need that

anymore we're going to grab a shape

object and we're going to print the

shape count we expect to get a one

because we just have one shape at this

moment we're going to create a second

shape here and if we print the count

we're going to get two because we have

two shapes this is what we expect we

create another shape which is going to

be shape three here we print the count

we're going to get a three but the

problem is going to come when we create

an ellipse here if we create an ellipse

and print the count we're going to get a

four because we have four shapes in our

c plus plus program but if we print the

ellipse count here we expect to get a

one but that's not what we're going to

get we're going to get a 4 because the m

count variable in ellipse is inherited

from our shape class so it is going to

be the same thing we have in shape here

because if you go back you're going to

see that at this point ellipse doesn't

have a static variable m count of its

own so it's going to use the one it is

inheritance from the shape class this is

the behavior we're going to get here and

i want you to be aware of this if this

is what you want this is fine but in

most cases you will want this to be

different because you want very clear

information about how many objects of

each type you have created in your

z-plus plus program if it is just shaped

this is going to be really vague because

you want to know if it is an ellipse if

it is a rectangle if it is a triangle

this is not going to be super clear so

let's weld and really show you the

problem here we're going to pass this

through gcc our favorite compiler we can

also bring up the left sidebar no

problem here and we're going to bring up

a terminal window or a powershell window

and run rooster you're going to see that

the shape count is going to be one two

because we are also incrementing the m

count variable in our derived class so

we are incrementing twice if we create

an ellipse object let's show you this in

ellipse cpp we are incrementing the m

count member variable but in the base

class we are also implementing that in

the cpp file that's what we have here

and notice that the derived class is

through our initializer lust here so

this is the behavior we have we

shouldn't be incrementing this because

ellipse doesn't have its own static

variable as of now now we're going to

build and really solve this problem now

you see the kinds of problems you can

run into if you have a static variable

that is named exactly the same way and

you have an inheritance hierarchy

really weird problems can pop up and you

need to be aware of this let's build and

see that the problem actually

disappeared okay the bolt is good we can

and run rooster we're going to see that

now this is what we expect one two three

because we have three shapes created up

to this point here if we create an

ellipse that's going to be another shape

if we get the shape count we're going to

get a 4 but ellipse count is also giving

us a 4 because ellipse doesn't have its

own static variable to solve this

problem we can go to ellipse and set up

our own member variable at the ellipse

level so we can enable this and

uncomment it we're going to go to the

incrementing to get the correct count

incremented here i think this is all we

need to do we are also going to

initialize the static variable we have

at the ellipse level this is going to do

what we want and we can build again now

we're going to get the behavior we want

because at this point we are going to

for the ellipse count and this really

makes sense because we have one ellipse

even if we have four shapes in total so

makes more sense in our c plus plus

program here we are going to build this

again and pass this through gcc the

builder is going to be good we can clear

and run rooster now we're going to see

that we have four shapes and one ellipse

this is what we want now that we have

this we can really do all kinds of crazy

things hopefully you can see that the

static variable is working exactly as we

want we can print the ellipse count we

can print the shape count if that's what

we want in our c plus plus program but

polymorphism and get the correct get

count method called in our c plus first

program for example if we call the

getcount method on the basepointer that

is managing a shape we're going to get

this one called if we have a best

pointer that is managing an ellipse

we're going to get to this one called

this is going to be super cool let's go

up in our program and set this up we're

going to do this on the fly let's say

shape polymorphism and we're going to

say shift pointer and it is going to be

an array let's say shapes this is going

to do and it is going to be just an

array and we're going to initialize this

and store in a bunch of objects let's

put in a closing brace here let's go up

and see what we have for example we have

shape one and ellipse one we can use

these we're going to put in the address

of shape one and we're going to put in

the address of ellipse one this is going

and we can loop through these guys and

call the get count method so let's do

this we're going to say for auto s

and let's do a reference because we

don't want copies and we're going to say

in shapes and we're going to call the

gatecount method we're going to say s

and say getcount this is going to

give us the count and we can print this

out if we want we can say sddc out and

put a new line character here to

put a separator here we can copy what we

just used in our c plus plus program

here just to make sure this is super

clear when we print things on the

terminal here we're going to build our

program and see if it actually works the

body is going to be good we can clear

and run rooster we're going to see that

the count is going to be 4 for the first

iteration because we're going to be

calling the get count method from

shape because that's our base pointer so

this is what we're going to get we're

going to print the m count member

variable from the base class that's why

we have a four but on the second

iteration the object is ellipse and we

are using polymorphism because we are

going through a base pointer and this

base pointer happens to support the

virtual method get count we will get the

most specific one called on the current

object that our base pointer is managing

here and this happens to be an ellipse

so we're going to call the ellipse

version of our virtual function here and

we will get a one because we really have

one ellipse in our c plus plus program

this is what we see here this is really

all i wanted you to see in this lecture

static member variables with inheritance

and polymorphism and you need to be

aware of these little things that can

really be confusing especially for

beginners we are going to stop here in

this lecture the next one we're going to

learn about the final specification we

can use in our inheritance hierarchy go

ahead and finish up here and meet me

go ahead and finish up here and meet me

there in this lecture we're going to

learn about the final specifier used in

inheritance hierarchies this is going to

allow you to do one of two things you

will either be able to restrict how you

override methods in the derived classes

or you can restrict how you can derive

from base classes i know this is in the

air but we're going to look at a few

examples to really drive this home

suppose we have an inheritance hierarchy

like we see here the top class is animal

we can derive from this and have feline

you can have bird as a derived class

feline can be inherited to have a dog

and cat and you can derive from cat for

example to have wild cat and bulldog

from dog you can do all these things

here and this is inheritance hierarchy

we're going to be using to learn about

these things now here is a possible

implementation for the dog class which

is going to be inherited from feline

publicly as we see here but take a look

at the run method we are setting up in

dag we are appending a final specifier

and what this is going to mean is that

no downstream inheritance class will be

able to override the random method

further this is what we can achieve so

if we don't want our derived classes to

virtual method we can mark that method

as final in our class and we are

basically saying i am going to put in my

implementation but i don't want any

deriving downstream class to override

this method further if they do that they

are going to get a compiler error and

this is something we can achieve using

the final specifier in our inheritance

hierarchy again in this case we are

how people can override our own virtual

method in downstream classes or i

shouldn't really say our own method

because it may be coming from upstream

but you are restricting people from

overriding that method further in

downstream classes here okay so this is

the first use we have for the final

specifier but we can also restrict

people from inheriting altogether so

here we have a simple example to drive

this home we have our cat class it is

going to be inheriting from feline but

we are marking our cat class as final

and what this is going to mean if

anybody tries to inherit or derive from

cat in any way they are going to get a

compiler error and this is what we can

achieve with the final specifier again

there are two things you can restrict

how people override your virtual methods

if you want to restrict that from the

current class you can mark your virtual

method as final you can also restrict

how people inherit all together from

your class and if you want that behavior

you can mark your class as final using

the syntax we just saw in the slides

here okay now that you know these things

let's look at a few things that may be

interesting for example here is a simple

fact that you can create a class right

away in market as final and when you do

this nobody will be able to ever inherit

from this class in your program and if

we do this we will get a compiler error

for example this is one thing i find

interesting and i really wanted you to

know this another thing is that it is

possible to introduce useless virtual

methods in your inheritance hierarchy

for example if our cat class is marked

as final what this means is that nobody

will ever be able to inherit from this

class but we are going further in

setting up a virtual method which is

meant to be inherited or overwritten in

downstream classes but how do we get a

downstream class if we can't inherit

from the cat class which is marked final

so so we have conflicting ideas here on

one hand we are saying we can never

inherit from this grant class but on the

other hand we are setting up a method

that is meant to be used or specialized

in derived classes so this is something

that is interesting this code is going

to compile and i think maybe in future

standards of c plus plus they are going

to fix this problem and maybe give you a

compiler error if you try to do

something like this but at this point

you're not going to get a compiler error

this is just going to be valid c plus

plus syntax even if this is really weird

we have conflicting ideas here okay one

thing you should know though is that we

can override in a final class and this

is going to make sense because for

example the run method is coming from

and here we are just specializing that

so we are marking that as an override

here even if this is the final class so

be careful this is valid c plus plus

syntax this is going to work just fine

another thing you can do which is pretty

useless in your c plus plus program is

to introduce a virtual method and mark

it as final right away so again this is

really weird we have two ideas that are

conflicting the virtual keyword means

that we want this to be visualized in

the downstream classes but again we are

saying this method is final so no

downstream class will override this if

they try to do that they are going to

get a compiler error so this is again a

bunch of conflicting ideas c plus plus

is going to allow this syntax this is

not going to give you a compiler error

but this is weird and you need to be

aware of this okay now that you know

these ideas we're going to head over to

visual studio code and play with the

final specifier in our inheritance

hierarchy we will be setting up this

kind of inheritance hierarchy and we

will set up a bunch of virtual methods

and mark them as final i think we will

do that in the dog class and we will

mark a bunch of classes as final and see

that if we inherit from them we're going

to get a bunch of compiler errors so

let's do this here we are in our working

folder the current project is final and

we are going to bring in our template

files pretty quick we're going to use

this as our starting point we're going

and i am going to put in a bunch of

classes i have lying around on my system

because i don't want to set up these

classes that would be a waste of your

time just know that we are trying to set

up this kind of inheritance hierarchy

animal is going to be our top dog or

animal is going to be our top class and

we will be inheriting from this creating

an inheritance hierarchy we can play

with in our code here okay so we are

going to open this up in visual studio

code so let's do that by dragging and

dropping here this is going to give us

all these crazy classes we have

the top class is going to be animal and

it is going to be defining the features

any kind of animal we support you know c

plus plus program is going to have for

example any kind of animal will need to

breathe and we will set up this virtual

and we will be inheriting from this

animal class to create a feline class

and a bird class this is something we

did in a few previous lectures and we

are just reusing this inheritance

hierarchy here let's look at the feline

class the filament class is going to set

up a virtual method which is called run

and the method is going to be overridden

we can override the run method but

notice that we are marking that as final

okay so look at this the method is final

and what this means is that

no downstream classes inheriting from

doug will ever be able to specialize or

override this method further if they try

to do that they will get a compiler

error notice that this may be our method

or it may be a method coming from

upstream classes in this case the run

method was introduced at the feline

level you see it was introduced here and

doug happens to be overriding this

method here that's why we have the

at the same time we are going to mark it

downstream classes from overriding this

method further if we look at our bulldog

class we're going to find the class to

inherit from dark we have our run method

here it is commented out at this moment

i just want you to see that our code is

just going to compile if we compile it

let's do this we're going to pass this

through gcc okay you see the bolt is

good and we have generated our binary

which is really not doing anything

because our main function is just some

dummy code we have here to make sure it

works with c plus plus 20 but what i

is that if you go in bulldog let's go in

our bulldog class and uncomment

this class here or this virtual method

we're going to see that we're going to

get a compiler error we have a squiggly

line meaning that we did something wrong

and well let's look at the problems tab

from visual studio code here cannot

override find a function dog run this is

the dog class if we try to override it

further we will get a compiler error

this is something we can achieve by

marking our virtual method as final as

we are doing here now if we try to build

this program we're going to get a

compiler error let's pass this through

gcc and let you see this okay you see we

get a compiler error and uh the error is

that we are overriding let's go up and

see the error here error and on line 12

in bulldog h we see that we are

overriding a final method virtual

void bulldog is a final function and we

are overriding this and this is going to

give us a compiler error this is the

behavior we get so the message here is

that you can go in your inheritance

hierarchy at any level and mark a

virtual method as final and prevent

download stream classes from

specializing or overriding that method

further and if they do that they will

get a compiler error this is something

we can achieve in our c plus plus

program another thing you can do with

the final specifier is that you can

prevent people from inheriting from your

class altogether let's go to our cat

class i think that's the example that

sets that up we have a cat class it is

going to be inheriting from feline but

the class is marked as final

now what this is going to do

it's going to throw a compiler error

anytime somebody tries to derive or

inherit from this class here so if

somebody tries to inherit from cat as we

are doing here create a wildcat from a

cat we are going to get a compiler error

because we can't inherit from cat

altogether it is a final class at this

moment okay so let's look at our wildcat

derive from cat we can do something like

this we can remove our comments here and

if we try to do this we will get a

compiler arrow let's look at the cpp

file and see what we have it has nothing

special but if we try to do that and

inherit from cat we will get a compiler

error because the cat class is final and

you cannot derive from it if you do that

you will get a compiler error because

the cat class is final this is what i

want you to see here let's try and build

our program again we're going to pass

this through gcc and we will see our

compiler error okay the world is

finished with errors if we go up we will

see that we cannot derive from a final

base class if we do that we will get a

compiler error and this is what i want

you to see here okay now that we notice

we're going to take this back

and take out the compiler error here

because we want our code to compile

we're going to make sure it is compiling

fine okay now the code is compiling

because we are no longer trying to

inherit from cat and i want you to now

see a few interesting facts about the

final specifier when it works together

with virtual functions let's go to the

main cpp file and show you the first

fact and that's that you can create a

class right away and mark that as vinyl

as you create it as we do here if you do

that this class is going to not be

inheritable and if you try to inherit

from it you will get a compiler error

let's take out everything we have here

and just say hello in our main function

this is going to do just to have

something this is going to give us a

compiler error because we can't inherit

from a final class let's build and show

you the compiler error this is going to

go through gcc and the world is going to

finish with errors and that we have our

message here and we don't have the error

we expected because we forgot to put our

closing semicolon on our class

definition here but we can build again

and get our error okay the world is

and the error is going to be that we

cannot derive from a final class this is

what we expect here let's comment this

out because i just wanted you to see

this fact another interesting thing c

is to set up a new virtual method in a

final class let's first build and make

sure the compiler error here goes away

and i am going to show you that okay the

build is good let's go back in our final

class which is the cat class

if i remember correctly this is a final

class we can't derive from this class

but we can set up a virtual method for

the virtual method here called meow is

why is it useless it is a virtual and

marking it virtual means that

you at least want people inheriting from

this class to inherit it and use it or

even better you want them to have the

or override this method and make it to

do more specialized things but you can't

really do that because you can't derive

from this class all together so this is

something that c plus plus allows us to

do but this is a useless method which

will never be used in any way so this is

something i want you to be aware of but

this is going to compile again let's

pass this through gcc you're going to

see that this is going to compile and

work even if this method is really

useless i want you to be aware of this

okay so the build is good here okay so

this is our interesting fact number two

okay even if this method is useless

it is possible to specialize a method

coming from upstream classes from your

final class for example in feline we

a method called run which was introduced

there i think we can override this

method in our final class which is the

cat class here so this method is going

to be useless because it will be

specializing what we get from our

upstream class this is going to work

okay so since we are looking at a few

useless things you can do with final

virtual mechanisms in c plus plus i want

you to see that it is possible to set up

a virtual method and mark it as a final

in the same declaration and we're going

to go to the bird class and really show

we have a virtual method which is called

fly but this is marked final the moment

we declare it and this is going to be

contradicted for example the virtual

keyword means that people downstream

will be able to specialize this or

inherit this but at the same time we are

marking this guy as final so we are

saying nobody downstream will be able to

override this method if they do that

they will get a compiler error now which

one is going to win virtual or final

final is going to win because if you try

to override this method in downstream

classes you will get a compiler error

let's go down and look at one bird we

might have in our program for example we

might have a pigeon let's grab this

method and try to override it you're

going to see that we get a compiler

error we're going to go in pidgin and

put in the fly method and uh for example

we're going to say pigeon fly here and

we're going to say override we are

trying to override this method but we're

going to get a compiler error you see we

have a squiggly line because this is a

final method and we are trying to

override this in a downstream class

and this class is a downstream class

from bird and in bird we map this method

as final so this is not going to work

even if this is virtual you want to be

able to really use the virtual mechanism

because this is final if we try to

inherit from this if we try to override

this like we are doing in pigeon here we

will get the compiler error let's try

and build our program and we will see

that we get our trusty compiler error

the bullet is going to finish with

errors and if we go up we're going to

find our error we're going to say

virtual function fly overriding final

function we are overriding a final

virtual method and this is going to give

us a compiler error we can't do this

this is something you can do in your c

plus plus program so this is really

confusing because in bird the virtual

keyword suggests that you can really

specialize this in downstream class but

this is contradictant and c plus plus

allows you to do this you need to be

aware of this again if we don't override

this and leave this in the code is going

to compile but in my opinion this is

really confusing and you need to be

aware of this that's the whole point of

this lecture here let's make sure the

code is building and this is really all

i had to share in this lecture

introducing the final keyword to you you

can use it to restrict how people

override your virtual function or you

people from inheriting from your class

altogether and use these things if they

make sense for whatever application you

are designing with c plus plus we are

going to stop here in this lecture and

the next one i am going to show you a

secret you probably didn't know so go

ahead and finish up here and meet me

there in this lecture we're going to

explore how virtual functions or

polymorphism plays with default

arguments and when we say default

arguments we mean a setup like this we

have a virtual function here which is

called add it is going to return double

default parameters here for a and b and

the value is five here in our derived

class we also have the same function we

are overriding that and we have a

different set of values acting as our

default parameter here we are using 10

for a and b here and we want to see how

this plays with polymorphism now please

note that with polymorphism if we go

through a base pointer to manage a

derived class object what we want is to

call the most specific implementation of

the virtual function here for example if

we have a base pointer managing a

derived object and we call the add

method from a base pointer we will get

the most specific method here called

but what you get with these default

arguments is that the compiler is going

to use static binding to decide which

default parameters to pass to your

function so even if you will get this

method here called the compiler will

still use the default arguments we have

in our base class so we will call this

method here but we will use the default

arguments coming from the base class and

this is the behavior you need to be

aware of okay so another way to put this

is that default arguments are handled at

compile time the compiler is going to

wire these things at compile time where

you are building your application

and the virtual functions are called at

run time with polymorphism so if you use

default arguments with virtual functions

you might get weird results with

polymorphism because the default

arguments you will be using are going to

be decided by static binding but the

actual function that you get called is

going to be decided by dynamic binding

so we will call the virtual function in

our derived class but we will be using

the default arguments from the base

class this is the behavior we'll get you

need to be aware of this and make sure

this is what you desire my personal

preference is to not use default

parameters or default arguments with

virtual functions because this is really

going to make my code hard to follow and

hard to understand especially for other

developers that might have to work on my

code base in the future okay here is a

simple example we have a base pointer

which is going to be managing a derived

object and we will call the add function

here what do we expect to get well

because we have polymorphism here we

will call the most specific add function

here and that's going to be the add

function from our derived class

but the default argument we pass are not

going to be decided by the derived class

the default arguments are going to be

plugged in at compile time using static

binding so because the base pointer is a

base object we will be using the default

arguments from the base implementation

of the add method so we will just plug

in five and five so we will add five to

five and add a two that's why we get a

and if we go through these references we

will get the same result because this is

going to enable or trigger polymorphic

behavior in our c-plus programs if we go

through direct objects we will be doing

static binding and we will use the

default arguments or device parameters

from our derived object and remember

that we use the value of 10 in there so

we are going to add 10 to 10 and add a 2

and we are going to get a 22 as you see

here through static binding if we do

slicing by assigning a derived object to

a base object the derived information is

going to be sliced off and if we add we

will use the default parameters from the

base class and we will use the

implementation in the base class so if

we come back to our code here we will

use the default arguments from the base

class and that's a five and a five we're

going to add them up because the body is

going to be from the base class remember

the derived information has been

completely sliced off so we are going to

add a five and a five and a one and

we're going to get 11 printed out if we

do slicing and that's the result we get

right here as a closing note before we

head over to visual studio code again

default arguments with virtual functions

can be very confusing they are best

avoided because they really are going to

give a hard time to anybody that is

going to be working on your code in the

future now that you know this we're

going to head over to visual studio code

and play with this a little more here we

are in our working folder the current

project is virtual functions with

default arguments we're going to grab

the code from our template project we're

going to copy this and put this in the

current project and i am going to grab

my classes base and derived that we are

going to be using here if you don't want

to type along you can grab the source

code from the resource section of the

if you don't want to type all these

classes or create them you can grab the

source code from the resource section on

this lecture you're going to download

this and use this you don't have to

waste time typing these things because

many of these things are already

familiar to you we're going to open this

in visual studio code and we're going to

have our classes here we have a base

class which is going to have a virtual

a pair of default arguments here we are

and if we go and derived it is going to

derive publicly from base and it is

virtual function here but notice that it

default parameters so if we do

and use the base pointer to call the add

method here we will get the most

specific or the most specialized version

of the add method called and this is

going to call this body here

but the parameters are going to be

decided by static binding so because we

will be going through a base pointer we

will use the default arguments from the

base class that's going to be five five

and we're going to play with this and

see what this is going to give us in the

main cpp file here let's clean up a

little bit we're going to remove

and we are going to include our derived

class we can do that we are going to put

in our code to really play with us let's

remove these spaces because we don't

need them we are going to go through a

base pointer to manage a derived object

and this is a setup we can use to put

things in place here we are going to

call the add method notice that we are

not passing in any parameter because we

are going through a base pointer and the

polymorphism will kick in and we will

of our add function code so we will call

be careful because we want to be using

these default parameters here if we did

we would add a 10 to a 10 and get to 22

in our main function here but that's not

going to be the case the compiler is

going to use static binding to decide

which default parameters to use either

those in the base class or those in the

derived class and notice that if we

hover over this add function you see

that the compiler has plugged down those

from the base class and that's what the

compiler is going to do so it is going

to add a five to a five and it is going

to add two to that i think that's what

we are doing in our derived version and

we are going to get to 12 printed out

let's build and see if this is actually

the case we're going to pass this

and that's the compiler that is our

favorite now the book is going to be

good we can close this and bring up a

powershell window and if we run rooster

we're going to see that the arrived ad

was called and the result was 12 here

the compiler is going to call the most

specialized virtual function override

here but it is going to use the default

parameters from the base class you

should really note this and this can

really be confusing especially if you

are a beginner to polymorphism if we go

through a base reference we will also

so if we have a derived object and we

set up a reference to that which is of

type base and we go through that base

reference and called the add method we

will get the most specialized add

version called so that's going to be

derived and but we will use the default

parameters from the base class because

which default arguments we use is

decided by using static binding that's

what we get here and official studio

code is really helpful here because if

we hover over the add function we're

going to see which default parameters

were plugged in by the compiler and you

see that they are those from the base

class so we are again going to add five

to a five and we are going to add a two

and we will get 12 printed out here if

we boil and run we're going to see that

this is the case the build is good we

and run rooster we're going to see that

with a base reference we're also going

to get a 12. we will get the most

implementation of the add method called

but we will plug in the default

parameters from the base class i really

wanted this to be super clear if you set

up things in a way that you are going to

get static binding then if you are going

through a base object you will call the

base version of the add method and you

will use the default parameters from the

base class if you happen to be

manipulating a derived object you will

use the information in the derived class

the derived version of the add method is

going to be called and we are going to

use the default argument from the

derived class so if we set up another

example here we can set up a base object

for example we're going to say base and

3 we can do that and we try to call the

add method we can say base 3 and say add

we can try and store this in our

research variable and we can print this

out we're going to say sdbcl row

research we can say something like this

and we're going to print out the result

here if we build and run we're going to

see that this is going to call

the base version of the add method and

it is going to use the default

parameters from the base if we go back

to base we're going to see that we are

going to add a 5 to a 5 and we will get

11 because we will plug in a 1 and

return the result here let's build and

run and see that this is actually the

case so this is going to be completely

doing static binding let's clear and run

you see that the world is good we're

going to run restaurant and we will get

11 printed out here hopefully you can

see this if you assign a derived object

a base object you will get slicing

let's see that we can actually do this

but before we do that i also want you to

row direct objects of derived classes if

get the information from the derived

class we will use the body from the

derived class and we will use the

default parameters from the derived

class so we will take 10 and add a 10

and we will add the 2 to that and we

will get a 22 printed out i think we can

let's put in a separator because that's

going to make it easier to follow these

lengths and we're going to build with

the gcc the both is going to be good

the bulk is good we can clear

and run rooster and we're going to see

that we get a 22 here if we assign a

derived object to a base object directly

by doing something like this event we

we can remove this we have a base object

that we are setting up here and we are

assigning a derived object to this base

if we call the add method we will get

the version from the base class because

mind your steps this is going to slice

off all the derived information because

we are not going through any kind of

base or reference so this is going to

slice off all the information we have in

object here and we will be left with the

base information and if we call the add

function here you see that we are using

the default parameters from the base

class and we will use the body of the

base class implementation here so we

will add a 5 to a 5 and we will add 1 to

that and we will get 11 printed out as

we see here let's build and actually

prove this we're going to pass this

through gcc the world is going to be

good we can clear and run rooster and we

are going to see that the result is

irreverent if we do row object

assignment here this is really all i

wanted you to see in this lecture that

you should really be careful if you are

mixed up with default arguments the

compiler is not going to do dynamic

binding on the default parameters it is

going to decide which default parameters

to plug in at compile time using static

binding so the compiler is basically

going to look at the type of the pointer

or object that you have and it is going

to use that to decide which default

parameters to plug in so at this example

here for example at line 7 it is going

to see what kind of pointer do i have i

have a base pointer so i am going to use

the default parameters from the base

implementation and if you hover over

here you're going to see that it is

going to plug in a 5 and a 5. even if we

are using the most specialized add

version in our inheritance hierarchy the

compiler is going to still use the

default argument from the base

implementation down here on line 16 the

compiler is going to say which kind of

reference do i have it's going to say

base because that's what we have here so

it is going to use the default

parameters from base and that's what it

is going to plug in here 5 and 5 and

we're going to get this result here

down here on line 25 the compiler is

going to see which kind of object do i

have here this three is a base so i am

going to use the default parameters from

down below on line 31 the compiler is

which kind of object do i have here the

object is derived so i will plug in the

default parameters for it derived again

this is really what the compiler is

going to do with default parameters the

compiler is never going to do dynamic

binding and this is going to make your

code really confusing again my advice is

to avoid default arguments or devote

parameters if you are using polymorphism

in your inheritance hierarchy we are

going to stop here in this lecture and

the next one we're going to learn about

go ahead and finish up here and meet me

there in this lecture we are going to

explore virtual destructors and these

are destructor methods you might want to

using dynamic binding or polymorphic

we are going to be using this

inheritance hierarchy to play with

thanks so the animal class is going to

be our base class we are going to derive

from that publicly and have a feline

class and we are going to derive from

feline and have a dog class this is the

setup we are going to be using here

now let's look at some code we are going

to set up our animal class like there's

nothing really special here notice that

the destructor is a regular destructor

we will derive from animal and create a

feline class which is going to set up

its own virtual function which is going

to be run if you want you can override

the breathe method but we don't want to

do that here because we just want to

on the destructors here and the order in

which they are going to be called we are

going to derive from feline and set up a

dog class and this dog class is going to

set up its own virtual function and

notice that it has a destructor which is

really a regular destructor now once we

have this inheritance hierarchy set up

we might want to do something like this

we can create a dark object

and when it is time for this object to

be destroyed i want you to focus on the

order in which the destructors are going

to be called we have seen this before

the destructors are going to be called

from the specialized to the most base

implementation of the destructor so the

destructor for doug will be called first

then we will call the destructor for

feline then we will call the destructor

for animal now a problem is going to pop

up if we are using a base pointer to

manage a derived object with polymorphic

behavior that we might want for our

inheritance hierarchy here so we are

going to use an animal pointer to manage

a dark object like this and when it is

time to release the memory for this

we may be tempted to call the delete

operator on our animal pointer here but

this is only going to call the

for the base class and hopefully you can

see the problem here because our

destructors are not virtual the compiler

is going to use static binding to decide

which destructor to call so it is going

to look at the type of a pointer it is

going to see that it is an animal

pointer and it is going to decide to

call the destructor for animal here

that's why we get this reserve we are

managing an object which is not just an

animal it has derived information in it

but we are only calling the destructor

for the base part of this stun so any

piece of dynamic memory we might have

allocated in the constructors for feline

or dog is going to be leaked out because

remember even if this is a dark object

it is made up of base parts the

foundation for this is going to be

animal and on top of that we are going

to build a feline level and on top of

that we are going to build a dog level

in this case only the destructor for dog

is going to be called and any dynamic

memory that might have been allocated at

the feline and dog level is going to be

leaked out and this is something we

don't want you really need to keep your

eye out on this and this is something

really bad you really need to keep your

eye out for this so this is really a big

problem and to solve it we need the

destructors to be called using

polymorphism and you can set that up by

marking your destructors as a virtual if

you do this the compiler will know

that if you are going through a base

pointer to manage a derived object when

the time comes for the memory to be

released and you release the memory

through a base pointer the compiler is

going to call the most specific

destructor it can find and this is going

to solve our problem then we will reuse

the order we are familiar with the most

derived destructor will be called and it

will call its best destructor and that's

going to happen until we hit the most

base class in our inheritance hierarchy

and the memory is going to be released

exactly as we would want now that you

know this we're going to head over to

visual studio code and play with us a

little more here we are in our working

folder we are going to learn about

virtual destructors and before we do

that we're going to grab our template

files and put them in place let's do

that and i am going to put in the

classes that make up our inheritance

hierarchy our most based class is going

to be base our most based class is going

to be animal after that we're going to

derive we are going to derive from that

and create the feline class and we are

going to derive from feline and create a

dog class here this is the inheritance

hierarchy we talked about in our slides

okay we are going to open this up in

visual studio code and this is going to

give us our classes here and we are

going to remove these virtual keywords

what would happen if you don't mark your

destructors as a virtual we're going to

do that for feline we're going to do

that for doug let's remove the virtual

keyword here we're going to remove that

and we're going to remove that for the

animal class and we want to see the

implementations for our destructors for

animal we are just going to say that the

destructor for animal was called for

feline we're going to say the same thing

feline destructor called for doubt we're

going to say the same thing we're going

to say destructor for dog called here

we are using strengths as our parameters

here so i think it is a good idea to

change these guys to use string view i

and come back when this is done

okay this is done all our parameters are

of std string view type and now that we

have this inheritance hierarchy let's

make sure none of the destructors is

virtual this is the case here we can

head over to the main cpp file and use

this inheritance hierarchy here we're

going to crack it open and remove

we are going to include our dog class

which is going to implicitly include or

its parent classes so we're going to

include dog.h here and we are going to

create a row.object by default here

we're going to say dog and let's say dog

one we can do that and we might not even

give it any parameter this is going to

call the default constructor and if we

go to doug we're going to see that it is

possible to specify information here

first style description but we're going

to ignore this and we just want to see

which order in which the destructors are

called let's build and run this program

we're going to pass this through gcc the

book is going to be good if we clear

let's bring up a powershell window to do

and run rooster you're going to see that

dog destructor was called feline

destructor was called animal destructor

was called and this is really cool this

is the order we expect by default but if

we don't do something like this and say

animal pointer and say p animal to mean

a pointer to animal and we say new dog

we're going to allocate a dog on the

heap and we're going to manage that

using a base pointer and if we try to

release the memory here let's do that

we're going to say delete p animal let's

see which destructor gets called here

because notice we are using a base

pointer to manage a must specific object

here which is a derived class of dog

indirectly and we will see that we don't

get the destructors called in the order

that we expect let's build and run this

program to really see this we're going

the world is going to be good as you see

and run rooster now you see that only

the destructor for animal is called even

if we are really managing a dog object

for things to work really well we would

expect the destructor for duck to be

called and then the destructor for a

feline and then the destructor for

animal to release or the memory that

might have been allocated by these

parent classes for our dog class if you

go back in the cpp file for example for

each of these classes you're going to

see that the compiler is going to be

each base class of the current level

that we are at in doug cpp we are going

to call the constructor for feline the

constructor for feline is going to be

called if it is doing any dynamic memory

allocation we need to release this

memory constructor for feline is also

going to call the constructor for animal

and if animal is doing any dynamic

memory allocation this is going to need

to be called but notice that we are just

colon the destructor for animal and if

we only call this destructor all of the

memory that was allocated by the filing

constructor is going to be leaked out

because only the animal destructor is

going to be called hopefully you can see

the problem here but this is not the

only problem the c plus plus standard

says that if you do something like we

are doing here and call a destructor

using a pointer to the base class but

that pointer happens to be managing a

derived object this is going to give you

undefined behavior so you're not

guaranteed to get to the same behavior

on different compilers on different

operating systems so this is something

really bad we want all the destructors

in our inheritance hierarchy to be

called to properly release the memory

that would potentially be dynamically

allocated by each level in our

constructor calls the fix for this is

really simple all you have to do is mark

your destructors as virtual and the

compiler will call the most specific

for your classes so all we need to do is

go in and mark these guys as virtual so

we're going to do that the base class

destructor is going to be marked as

virtual we're going to go to feline and

do the same thing we're going to mark

that as virtual and we're going to go to

and mark its destructor as virtual we're

going to do something like this and now

notice we don't need to change any other

thing if we build our program we're

going to pass it through gcc it is going

to do exactly what we want because

now the compiler will resolve the calls

to the destructors polymorphically

because we are going through a base

pointer the compiler will call the most

specific implementation for this

structure because we are going through a

base pointer to call the destructor here

the most specialized destructor we can

find and it is going to find the

destructor for duck which is going to be

the most specialized destructor we can

find in our inheritance hierarchy it is

going to call the dog destructor that's

going to go the destructor for feline in

turn and then that's going to call the

destructor for animal and our memory is

going to be released properly that's

what we're going to see here let's make

sure we weld this again because i'm not

sure if i actually built this the body

is going to be good anyway so we're

going to clear and run rooster now you

see that the duct destructor is called

the vlan destructor is called the animal

destructor is gold and everything is

just going to fall in place so my advice

if you are using virtual functions in

your inheritance hierarchy make sure you

also mark your destructors as virtual

this is going to save you future

headaches you might come in contact with

if you are using a base pointer to

manage a derived object and you are

doing some kind of dynamic memory

allocations in your constructors that's

going to release the memory properly if

you are releasing the memory through a

base pointer like we are doing on line 8

here this is really all i had to share

in this lecture i hope you found it

interesting we are going to stop here in

this one in the next one we're going to

go ahead and finish up here and meet me

there in this lecture we're going to

learn about dynamic casts and the

dynamic casts are a facility we have in

to do downstream transformations

so if we have a base planer for example

we can transform it to a derived type

and be able to use it like we use any

row object for example if we do this

kind of transformation we will be able

to call non-polymorphic functions and

this may come in handy sometimes

this is the hierarchy we will be using

our top class will be animal here we

will derive from this and create our

feline class and we will be live from

feline and create our dog class here if

we have a base pointer pointing to a

dark object for example the most

specialized class we can have in our

inheritance hierarchy sometimes we might

want to transform from this base pointer

to the most derived object here and get

to the direct most derived object that

we can really call anything on if you

remember with a base planer like animal

here the only thing we can do is really

polymorphic or virtual functions but

sometimes we want to do much more than

this for example if we want to call

non-polymorphic functions this is not

going to work because the best pointer

has no knowledge of those functions so

if we need to do that explicitly

transforming from a base pointer to a

derived pointer is going to give us that

capability if the actual object we are

pointing at happens to have that method

okay so this is what we are after in

this lecture we want to be able to

transform from a base class pointer

or reference to a derived class pointer

or reference at runtime another way you

can text this is to think of the base

class pointer or reference as input and

we want to get a derived class pointer

or reference as output in our c plus

plus program and the main benefit of

this is to be able to call

non-polymorphic methods on derived

pointers or references this is going to

be super cool in some cases okay so

let's look at our inheritance hierarchy

here the top class is going to be animal

as you see here it's going to have a

single virtual method it's going to also

have a virtual disruptor because we know

how to do this now we can derive from

this and create our filling class which

inheriting publicly it's going to have

its own run method and it's going to

declare its own other method which is

not virtual we can also derive from

feline and create a dog class this is

how we do this and we're going to set up

our own virtual method in dog which is

going to be bark and we can really do

anything we want with this inheritance

hierarchy okay what we're going to be

using as input is a base class pointer

or a base class reference and we set

them up here this is our base pointer

this is our base reference and we want

to go from these and create a derived

class pointer or reference that we can

non-polymorphic functions and we can

achieve that using dynamic casts here

we're going to show you how you can cast

pointers again our animal base pointer

is going to act as our input and the

output is going to be what we want to

get out of this transformation

and all we do is say dynamic cast we

specify a pair of angle brackets inside

we're going to specify the output we

want to get and this is usually going to

be a derived class pointer so the base

class pointer is going to be within this

parenthesis and and it's going to be our

output and this is going to do the

transformation and it's going to give us

a result that we're going to be storing

in our feline pointer here and if this

succeeds we will have a valid feline

pointer here and we can use it to call

non-polymorphic or non-virtual functions

like we are doing here and this is super

cool another thing you can do with this

is use the result of this transformation

in a pointer check for example we can

check and see if this pointer is not a

null pointer if it's not a null pointer

we can call our non-polymorphic function

to it the result was successful but if

it's no pointer we're going to fail and

fall down here and we can say that we

couldn't cast to a feeling pointer and

how can this transformation fail well if

we go back to our code here we have an

animal base pointer which is really

pointing to a feline object in memory

if we try and cast this animal pointer

suppose we want to do this kind of

transformation try to think about this

this is not going to work because we

really have no dog information in this

villain object and if we try to cast

this to dog the compiler will really

have no way to do this and the

transformation through dynamic cast will

fail and we will say the message here

meaning that we couldn't do the

transformation the user asked for so

here we can do the transformation and

transform from a base pointer to a

derived pointer but we can also

transform to a derived reference and i

am going to show you the syntax to do

that and it is super simple we say

dynamic cast and we specify our input

notice that this is a reference you have

to put it it's not a pointer and you

specify the output within this angle

brackets here once you do this the

output of this is going to be a derived

reference and we're going to store this

in our feline reference here once we do

transformation is successful we're going

to be able to call our non-polymorphic

function this is going to work but with

references we don't have the luxury to

do something like a pointer check

because there is no such thing as a null

reference a reference is always pointing

and if the transformation fails we will

have some kind of invalid reference and

if this fails it is probably going to

blow up and give us undefined behavior

so you don't really want to do this i

doing this kind of transformation with

references unless you know

that the transformation is possible

beforehand what i usually recommend is

pass through pointers and it is even

possible to transform a base reference

into a derived pointer and the syntax to

do that is what you see here okay and uh

once we do a transformation to a pointer

if the transformation is successful

we're going to have a valid pointer in

here if the transformation fails we're

going to have a null pointer and the

check is going to draw us here and we're

going to print this message to say that

we can't do the transformation here okay

again the cast may fail if it fails

while we are trying to transform it to a

dog pointer we are going to fall down

here and say that the cast failed we can

also do the same thing through

references for example if we want to

transform this base reference to a

and this fails we're going to follow

here because of the check we are doing

here we can do something like this to

make our code much safer to work with

and another thing i should really point

casting like this is usually done in

functions where you are passing a base

pointer or a base reference as a

parameter and in this function you

somehow need to call a non-polymorphic

function so you might do something like

this and take the pointer and turn that

into a derived pointer and if the

transformation is successful you're

going to call your method and if the

check fails you're going to follow here

and print an error message you can do

something like this with pointers and we

can do exactly the same thing with

references but here because we want to

do this check we're going to transform

our base reference into a derived

pointer and call our method on the

derived pointer instead this is going to

give us the ability to do this kind of

check to make our code much safer to

work with a word of caution here

overusing down casting is a sign of bad

design if you find yourself doing this

kind of thing a lot to call

non-polymorphic function that's maybe a

sign that you should make that

polymorphic because that's going to save

transformations a lot just make sure you

don't overuse this and do it in a few

cases where you really need to do this

kind of thing now that you know this

we're going to head over to visual

studio code and play with us a little

more here we are in our working folder

the current project is dynamic casts

we're going to grab our template files

and we're going to put them in place

let's do that and we are going to grab

the files that make up our inheritance

hierarchy we're going to put those in we

have animal dog and feline and this is

going to make up our inheritance

hierarchy here once we have this in

place we can open this up in visual

studio code by dragging and dropping

here and this is going to give us our

files okay we have our files in here we

can open up the animal class which is

our base class we can see that it is

really simple it's just going to have

one virtual method which is brief it's

going to have a single member variable

which is description here we can derive

from this and create our feline class

which is going to inherit publicly from

animal feline is going to set up its own

and we will have a virtual method called

run we can override in downstream

classes if we want to do that and let's

look at the implementation for feline

cpp if you want to do that you can take

a look it's just going to forward the

construction to the base class to build

let's look at dog dog is going to

inherit from feline and it is going to

set up a simple virtual function called

work and it's going to have a virtual

destructor now we know that we should

virtual disruptors if we happen to even

have a single virtual method in our

inheritance hierarchy because that's

going to make events easier now we want

to go to the main cpp file and play with

dynamic casts we're going to remove

whatever it is we don't need here and

that we can include our most derived

class let's include doug here this is

both feline and animal because this

header is going to include its parent

and its parent is going to include its

own parent this is the logic here we are

going to start out by using a simple

example here and show you that you can't

really call non-polymorphic functions

from a base pointer that is managing the

derived object and here we have an

animal pointer it is a base pointer and

it is managing a real feline object in

memory but if we try and call a

non-virtual function through this base

pointer this is going to blow up this is

we can't really call a non-polymorphic

function through a base pointer because

that's not a virtual function the

requirement to be able to do this is for

the function to be virtual and do some

feeling thingy is not a virtual function

that we know at the base level so this

is not going to work by default and if

we're trying to build code like this

this is going to give us a compiler

error let's pass this through gcc we're

going to do that we are going to finish

the world with errors and if we go up

we're going to find that class animal

has no member name to do some feline

thingy so this is the compiler error

here this is not going to work if we

need to do something like this one

solution might be to do dynamic casts

that we are learning about in this

lecture here and the syntax is

ridiculously simple so we can go down

here and put in a simple separator to be

able to follow this lens on our

powershell window you can do this if you

want and we're going to do our dynamic

cast for example if we wanted to do a

transformation and transform this to a

dark object this would give us a problem

and let's try and look at this again we

have a feline object here and we are

managing this through a base pointer and

what we want to do is to take this space

a dog object if you look at this

remember that we don't really have any

dog information in our feline object

this is going to just go up to the level

of feline but we want to transform this

to a dog to make this super clear let's

look at our inheritance hierarchy again

what we have is a feline object and the

information we have really goes up to

and we are managing our feeling object

through a base pointer this is the setup

we have but we want to do the

transformation and turn this base

pointer into a dog object and this is

going to blow up especially if we have

any dog specific member variables this

is going to blow up this is not going to

work if we try to access dog information

what we get through the transformation

to animal to dog we're going to get a

crush because we have no such

information and we're going to look at a

simple example to really drive this home

so what we're going to do is go back to

our dog class and we're going to put in

a sample member variable we're going to

make it private and for example we can

make this a member variable to keep

track of the speed for the dock we can

do this and we're going to initialize

this to 0 by default and we're going to

set up a function which is going to

print some dog information let's go back

to feline and copy the do some feline

thingy method and we're going to do some

dog thingy that's what we're going to do

here i am going to put in this method

and adapt it a little bit we're going to

do some dog thingy and we're going to

account for that in the body but we also

want to print the speed for this dog

here so we're going to say speed and

we're going to print this out suppose we

have this kind of setup in our

inheritance hierarchy here a dark object

has some doubt specific information it

has an additional member variable which

is m speed here we won't worry about

initializing this from the constructor

you can do that if you want all we

really want is to add some extra data at

the dog level and we're going to see

that if we try to transform to doug this

is going to give us a few problems so

what we want is to turn this animal base

pointer into a dark object let's do this

change this to dog and the result object

we get is going to be a dog pointer and

method on the pointer we get as a result

of this transformation here let's see

what happens you're going to see that

this is not going to give us any

indication that we are doing something

wrong but if the transformation here

fails this is going to silently fail and

store junk data in our feline pointer

here and here we're going to try and

call a method that is going to possibly

use some dog stuff on the feline object

this is going to blow up again we don't

have dog information in this feline

object and the do some dog thinking

method is going to try and print the

speed of the dog that we don't really

have we don't have any dog information

so we have no business accessing dog

information from this object to start

with so this is going to blow up and

it's probably going to give us a crash

let's try and build and see what happens

we're going to pass this through gcc

like we always do the boat is going to

go through you see that this is going to

even blow up at run time when users are

actually using your application this is

super dangerous we're going to run this

and see what happens you see doing some

dug thingy and it's going to try and

print the speed the compiler is really

trying its best but this is really going

to fail and we are crashing our program

if you go down here and say done to make

sure we know when the program is done

and we try and run our program again

let's pass this through gcc to take into

account this thing we have on line 20.

the book is going to be good you're

going to see that the computer is going

to try and really run this but it's

going to see that it doesn't really have

any dog information and the computer is

not going to succeed because we are

trying to access this dub specific

information really on a feline object so

we are going to get a crash again the

is that this dynamic casts can fail

and we need a better way to do some kind

of checks before we call our methods

here and we can do this by just using

the pointer we get from this

transformation here so we can say if

feline pointer and check and see if we

have some valid data in this villain

pointer and if that's the case we're

going to do whatever we want to do with

this pointer here okay so this is

and if the transformation fails we're

going to fall in this else block and we

can put some nice message here instead

of letting the user crash at runtime

this is much better in my opinion so

we're going to say couldn't do the

transformation from animal pointer to

dog pointer because we really have no

dog information and this base pointer

that we have here this is something we

can do so we're going to say sddc out

i'm going to say stdendl here and we're

going to see what happens let's build

hopefully we're not going to get the

crash because we are doing something

smarter now we are checking to see

if we have any dog information in this

pointer before we call some doubt

specific method on this pointer here

this is the beauty of this we're going

to clear and run rooster now you see

couldn't do the transformation from

animal to dog and our program is no

longer crashing it is ending properly

and this is much better this is what you

should aim for so again the

transformations here may fail

if we turn this back to doing v-line

transformation let's do feline pointer

we're going to change this to fill in

pointer again and we're going to do some

feline thing now we're going to bolt

we're going to bolt again and this is

going to build successfully and it is

going to probably do some filament

thingy the build is good we can clear

and run rooster this is going to work

just fine and our program is going to

end properly so here we just saw that we

could do a transformation from a base

pointer to a derived pointer and this is

going to work just fine we can also do

the transformation for references let's

say that here and we're going to go down

and put in a simple example to drive

this home we're going to have a feline

object we're going to set up a reference

to it and if we try and call a

non-virtual method on this base

reference this is going to blow up

the base class has no information about

this non-virtual method that we declare

at the feline level this is going to

blow up if we try to build our program

we're going to see that we get a

compiler error saying no such method

do some feeling thing we're going to see

this way at the animal level

this is the compiler error we get if we

try to call a non-virtual method through

a base reference that we have here this

is not going to work but we can also do

a dynamic cast and transform from a base

a derived reference and the syntax to do

that is really here we're going to set

derived reference in this case it's

going to be a feedline reference we're

going to initialize this with a dynamic

cast transformation and the result of

the cast is going to be used to

initialize this reference here and we're

a base reference and turning that into a

derived reference here this is the

syntax the output you desire is going to

be within this angle brackets and the

input is going to be through this

parenthesis here if this succeeds we

will be able to call our method here and

this is going to work just fine let's

we are going to put in a separator to be

able to follow these things let's put

that at line 24 here this is going to do

and we're going to try and build our

program we're going to pass this through

gcc the boat is good we can clear and

run rooster now we're going to see that

we are doing some filling thingy through

a reference and this is super cool we

can do this you can do this kind of

transformation here and at the end you

see that we are calling our destructors

on our objects and this is a good

reminder that we didn't properly release

the memory on this animal pointer that

so we are going to go down at the end of

the program and release that memory this

is good practice and hopefully you can

see how easy it is to forget to release

some memory that you allocate for

with the new operator this is a good

learning experience here but this is a

good learning experience here but we're

going to fix this problem we're going to

say animal one and we're going to

release the memory now if we run the

program we're going to see that we are

releasing two objects when the program

ends we're going to clear and run

rooster and the destructor is going to

be called two times once for this guy

and a second for this guy this is what

we want and you see that because we have

virtual destructors in our classes we

are destroying at each level so here we

are destroying at the feline level and

we are destroying at the animal level

and this is going to properly release

the memory from our inheritance

hierarchy here so now you know that you

can do a transformation of references

but with dynamic cast we have no way to

check and see if the transformation was

successful again if we try to turn this

into a dark reference we can do that and

we're going to say dog reference here

and we will try and call the do some

duck thingy method this is not going to

give us an indication of a problem but

this is going to crash at runtime

because we don't really have any dog

original feline object here so if you

try and transform this reference into a

dog reference this is obviously not

going to work because we have no dog

information in this to start with let's

boil and show you the problem the book

is going to be good so we can clear

and run rooster you're going to see that

we are going to terminate our program

with the band cast and this is going to

crush you see that we don't get to the

point where we print done and we are not

even going to get a chance to release

the memory that we have allocated in

this main function hopefully you can see

that this is really bad so with

to check and see if the transformation

was successful and this is a limitation

that's why in most cases i usually do my

transformations through pointers and

there is a way you can even turn this

base reference into a base pointer and i

am going to show you how you can do that

so we are going to go down here and try

to change things a little bit we are

going to say doing proper checks with

references and we're going to put in a

piece of code to play with us and what

we're going to do we're going to take

base reference and turn that into a base

pointer this is the syntax here again

the input is the base reference but the

output we desire is a base pointer and

this is possible in c plus plus this is

going to work just fine now we are going

to go on top and comment this

problematic transformation we just tried

to do and we're going to try and build

and see if this is actually working

if this transformation succeeds we're

going to do some villain thingy if it

fails we're going to say couldn't cast

to feline reference and we're going to

say that we are sorry this is a good

output message if we get something wrong

we're going to build this with gcc and

see if this actually works the world is

and run rooster you see that this is

working just fine we're going to hit the

end of the program and we are going to

destroy our objects here this is super

if we try and do the transformation and

transform it to a dark object even if we

know that we don't have any dog

information in this object that we are

referencing to start with we hope that

we're going to get a good message and

the program is going to end properly

we're not going to get a crush so let's

make sure we are transforming to dog

here we're going to pass a dog pointer

as our output and we're going to store

this as a dog pointer even if the name

is still vlan pointer hopefully this is

not going to confuse you even if this is

named feline pointer it is a dot pointer

here because we just want to see

if we get the error message that we have

here so we are turning this reference

into a pointer and the benefit of this

null pointers and we can use this to our

advantage to check and see if the

transformation here was successful if it

was successful we will call some dog

thank method let's say that here and if

this fails we're going to say that we

couldn't transform to doug and this is

going to give us a nice message and our

program is not going to crash we're

going to build this again with gcc what

is going to be good as you see here

we're going to clear and run rooster now

you see that we are saying we couldn't

catch the dog reference and our program

is not crashing so if you have a

reference to start with and you want to

do some proper checks after you do the

transformation to a derived pointer or a

derived reference this is the best of

both worlds you can do something like

this and your program is going to be

much safer the last thing i want you to

see is that these kinds of dynamic casts

are really useful if you are passing

base pointer or base references into

functions and here i am going to put in

a bunch of functions the first one is

going to take a base pointer the second

one is going to take a base reference

and it is going to say do something with

animal pointer and do something with

animal reference and inside we're going

to do our thing here we're going to take

the animal pointer turn that into a

feline pointer and we're going to do our

proper check and we're going to do some

feline thingy if the transformation was

successful we can do something like this

we can also do exactly the same thing

with references we're going to take our

input reference we're going to turn that

into a derived object and we can call

our method on this pointer and we're

going to do proper chats because we have

a pointer which has a concept of node

transformation here fails this is the

setup we can use in our c plus programs

and we can use these methods to get

derived pointers that we can call even

non-polymorphic functions on and this is

going to work really well so we can go

down and comment out everything i guess

to make this super easy to follow but i

don't think we need to comment out

everything we can just comment out what

we just did here and we're going to be

reusing the reference we have here and

the pointer we have all the way to the

top so we're going to go down and put in

a separator here we can do that and

because of this separator i don't think

we even need to comment things out we

can remove our comment and leave the

code in because i want you to see that

super easily and we're going to call our

functions here we're going to say do

something with animal pointer and we're

going to pass an animal one which is a

pointer and we're going to say do

we can do something like this and we're

ref we have this reference here and we

can do something like this you're going

to see that this is not going to give us

any kind of problem and it is going to

work just fine that's world we're going

to pass this through gcc the photo is

going to be good we can clear and run

rooster and down here you see that in

function taking base pointer doing some

feline thingy in function taking some

biz reference doing some feeling thingy

and this is working really fine this is

what we want in our c plus plus programs

this is really all i wanted you to see

in this lecture hopefully you didn't

find it confusing again the message is

that you can do dynamic casts to

transform from a base pointer to a

derived pointer or to transform from a

base reference to a derived reference as

right here but transforming to a derived

reference has a drawback in that you

don't have a way to check and see

if the transformation was successful so

if you want to be able to do chats you

can do something like this and turn a

base reference into a derived pointer

and then we can check and see if the

pointer is not a node pointer if it's a

no pointer we will know that the

transformation failed and we will print

a good error message if the

transformation was successful we will

have a valid pointer in here and we will

call our derived non-polymorphic method

on our pointer this is going to work

really fine the last thing i want you to

see before we wrap up this lecture is

that dynamic casts are only going to

work with polymorphic inheritance

hierarchies so for example if we try and

turn a double into a string obviously

that's not going to work with the

dynamic cast but let's try and do that

to really show you that this is going to

give us a problem we're going to say

sddc out and we're going to put in a

separator here and we're going to set up

two variables one is going to be a net

for example and we're going to say data

we're going to put in a 45 and if we do

a dynamic cast to an sdd string for

example that's not going to work we're

going to say std string yana str meaning

that this is a string we're going to say

dynamic cast let's say we want to turn

this into an sdd string for example and

the input is going to be our data if

you're trying to do something like this

this is going to blow up you see that

even visual studio code is giving us a

squiggly line so this is not going to

work just make sure you use dynamic cast

in an inheritance hierarchy that

supports virtual functions this is the

design purpose for the dynamic cast if

you use this outside this context you're

going to get undefined behavior or even

compiler errors if you are lucky let's

try and weld and show you this we're

going to pass this through gcc and we're

probably going to get an error saying

that we can't transform from an integer

to a string for example let's go here

cannot dynamic cast so basically it is

saying dynamic casts are meant to work

only with pointers or references but

even then let's see if we can transform

from an end pointer to a string pointer

let's try and do that let's say we want

to turn the address of data or let's set

up a pointer to be explicit we're going

to say data ptr and we're going to

initialize this with the address of data

we can do something like this and we're

going to cast data ptr to an std

strength pointer let's see if we can do

this because it is meant to cast

between pointers and references but you

see that this is even not going to work

so you shouldn't really do something

like this if your input and output are

not part of the same polymorphic

inheritance hierarchy again dynamic

from base information to derived

information and the input and output

must be part of the same polymorphic

inheritance hierarchy this is the

information i am trying to convey here

so this is bad don't do something like

this if you do this you're going to get

undefined behavior or you're even going

to get a bunch of compiler errors if you

are lucky this is really all we set up

to do in this lecture showing you that

you can use dynamic casts we are going

to stop here in this lecture the next

one we're going to show you what happens

if you try to call a polymorphic

go ahead and finish up here and meet me

there in this lecture i am going to give

you a warning and that is to never call

virtual functions from constructors or

destructors i am going to repeat this

never never call virtual or polymorphic

functions either from constructors or

destructors and we're going to explore

why we're going to be using this

inheritance hierarchy we're going to

have a base class called base how

creative we're going to inherit from

base and create derived which is our

inherited class and we're going to be

using this to explore why we can't call

virtual functions from constructors and

this is what our code is going to look

like the base class is going to have a

protected member variable it's going to

have a bunch of virtual functions

we will have a virtual function to set

things up and it is just going to set

the value of our member variable to 10

and we're going to have a virtual

function called cleanup which is going

to maybe do some cleanup we're going to

see how this works out we also have a

method to get the value but i don't

think we will use this but you can keep

this and if you want notice that we are

trying to call the setup method from the

and you see that we have a comment that

says that this is going to do static

binding but we're going to see why in a

minute so this is our base class we can

derive from this class and create our

derived class we're going to inherit

and we are going to override the methods

we have in the base class we're going to

override the setup method as you see

here we're going to override the cleanup

our destructor is also going to be

virtual because we are good c plus plus

citizens and this is the setup we have

once you have your inheritance hierarchy

set up you're going to do something like

this because you want polymorphic

behavior you're going to set up the base

pointer and you're going to use that to

manage a derived object and you can do

considering this statement here i want

you to think about the order in which

constructors and destructors are going

to be called we have touched on this

subject before and we are going to

revisit this because it is really

in terms of calling virtual functions in

destructors and destructors

so when we do something like this the

base part of this object is going to be

wealth first so we are going to call the

base constructor first we're going to

set up the best part of us after that

we're going to set up the derived part

of us and we're going to call the

and after the derived part of us is set

up we can use our object like we do

always so we're going to use our object

to do whatever it is we want to do when

the time comes for this object to be

destroyed we're going to destroy the

and then we're going to destroy the base

now that we have considered this order

try to think about the setup when we

from a constructor that's what we're

going to look at first the best

constructor is going to be called but

notice that by the time we call the base

constructor the derived part of us won't

be set up yet so if we try to call a

virtual function in the base constructor

there won't be a derived part to call

the most specialized method for so the

compiler will notice that we don't have

a derived part yet we will be at this

stage building the base part and if we

call a virtual polymorphic function we

want the most specific parts to be

called which should live in the derived

part but we haven't done the derived

part yet we are still building the base

part of us so the compiler is going to

notice that we don't have a derived part

and it is going to call the base version

of our virtual function that's why we

said that if you call a virtual function

from a constructor or a destructor

you're going to get static binding

results if you call a virtual function

you want the most specific version

called but we don't have that yet in the

base part because the derived part

haven't been set up that's why we get

static binding results i hope this makes

sense and we're going to get to the same

result if you try to call a virtual

function from a destructor if we get to

the point where our object needs to be

destroyed the derived part is going to

be wiped out first we're going to be

left with the base destructor and when

we hit this base destructor and call a

that would mean to call the most

version of that method but the derived

part of our object has been already

wiped down so this is no longer existent

and we are trying to call the method on

this so the compiler is going to do the

next best thing it can do it is going to

call the best version of our virtual

function and again we are going to get

static binding results that's why it

isn't really wise to call a virtual

function either from a constructor or a

destructor now some of you must be

asking what if i really need to do setup

and clean up in the way that we set up

these things in our classes what if this

method is really useful maybe it is

setting up things we're going to be

using in our application we really need

this and the most logical point to call

this is the base constructor well you

shouldn't really put these in a

constructor what you could do

is maybe call this virtual method on

your object directly when the object has

finished being a constructor that's

going to be a better place to do this

because if you put that in a constructor

or a destructor you're not going to get

dynamic binding results and that's going

to be really bad so to sum up calling a

from a constructor or a destructor want

to give you polymorphic or dynamic

binding results the call will never go

to a more derived class than the

currently executing constructor or

and we will get static binding results

this is the idea i want to convey here

and as a guideline you should never call

virtual functions or polymorphic

functions from constructors or

disruptors if you really need this the

next best thing you can do is to call

your virtual functions directly on your

object after the object has been

set up we can do something like this and

call our setup method and then we can

call cleanup when we think that we need

to clean up and you call cleanup after

you construct the object and you call

delete after you clean up your object

this is going to do whatever it is you

want to do with your polymorphic

functions and the calls to these virtual

functions want to be leaving inside a

constructor or a disruptor and this is

going to work really well now that you

know this we're going to head over to

visual studio code and play with us a

little more here we are in our working

folder the current project is

polymorphic functions and the structures

we should really say with constructors

and instructors but this is going to do

we're going to grab our template files

and we're going to put them in place and

we are going to open this little guy in

visual studio code by dragging and

dropping here this is going to give us

our main cpp file we can clean up a

little bit remove whatever it is we

don't need and i am just going to put in

my classes i am going to do that in the

main cpp file because that's going to be

much easier to follow we have our base

class it is going to have a single

member variable called m value and we

will have a virtual destructor

we will have a bunch of virtual

functions one is going to be setup which

is going to set our value the other is

going to be cleanup which is going to be

doing some cleanup here we will also

have a getvalue method which will get

this value and print it out if we want

but it is really not that useful here we

will also create a derived class which

is going to inherit publicly from base

it is not going to have its own member

variable all it's going to do is set up

the virtual functions we have in the

base class we're going to override setup

and in derived we're going to set our

value to 100 and we're going to clean up

and put a message that we are cleaning

up here once we have this set up we can

head over in the main function and set

up a base pointer which is going to be

managing a derived object a classic

setup for polymorphic behavior so we're

going to say base and i'm going to say p

bass and we're going to say equals new

derived this is going to give us our

object which is managed by a base

pointer and one thing i didn't show you

is that we are calling the setup virtual

from the base constructor this is what

we want to see we want to see what is

happening here now if we call this setup

we would expect polymorphism to kick in

because this is a virtual function

if the derived part is available we will

call the most specific setup function

and that would set up the value to be

100 here if we get the value that's what

we would get let's see what we get here

value that we have in this object here

so we will get auto value and we're

going to say p base get value we have

this function here and we will try to

print this out okay this is something we

can do in our c plus bus program and

we're going to see the value we get

because we are calling this virtual

function we expect polymorphism to kick

in and if polymorphism kicks in we're

going to call the most specialized

version of our virtual function here

that would be the override we have in

derived and that would give us 100. so

one would get to get 100 printed out

here but let's see what we get we're

going to run this through gcc our

favorite compiler the builder is going

to be good we can clear or bring up a

powershell window we're going to clear

now and run rooster we're going to see

that the base constructor is going to be

called base setup was called you see we

called the base version of this and the

derived constructor will be called and

we're going to see that the value

doesn't exist oh we didn't put the value

out let's do that my bad here we're

going to build again we're going to use

gcc to build and the world is good we

can clear and run rooster now we see

that the base setup method was called

and set the value to b10 and we are

really getting static binding results

because we are calling the setup

method from the base class and the base

version is being called so this is

classic static binding behavior but we

want polymorphic behavior to be working

here but we just saw the reason why this

is in the slides by the time we call

this virtual function we haven't set up

and we have no way to call this virtual

function which lives in the derived part

of us so the compiler is going to do the

next best thing it can do it's going to

call the best version of this method and

we are going to get static binding

results and we are going to get the same

results if we try to call a virtual

function from the destructor for example

if we go in our destructor here

let's see if we can find it we're going

to go in our instructor here and say

this and say cleanup can do something

like this and you're going to see that

the cleanup version we call is the base

and we don't really want to do something

like this we want the most derived

cleanup version to be called but we

won't get that because by the moment we

call this virtual function from our base

the derived part will already have been

wiped out so it won't be available and

the compiler will do the next best thing

it can do it is going to call the best

version of our cleanup function here i

again to really drive this home i

realize this can be confusing to many

people especially beginners if we are

calling a virtual function from a

constructor we will call that virtual

function when we hit the base

constructor but by the time we hit the

base constructor the derived part of us

hasn't been constructed yet so if we try

to call a polymorphic function needing

to hold the derived implementation that

won't be available and the compiler will

do the next best thing it can do it is

going to call the base version the same

phenomenon is going to happen in the

destructor when we are done using our

object we will destroy the derived part

information first and when we hit the

base destructor and call a virtual

function there won't be a most

specialized version of the virtual

function because the derived part has

been already destroyed and it doesn't

exist anymore so if we call a virtual

function from the base destructor we

will get the best version called and

this will give us static binding

behavior this is what we are

experiencing here okay so let's try and

run this program and see what we get we

will print out value here which is going

to give us static binding results but we

want to see which version of cleanup is

called this is what we want to see here

we're going to run the task to build

with gcc the world is going to be good

as usual we're going to clear and run

rooster and i'm going to see base

constructor called derived constructor

called and we're going to have a value

which is a junk value because we never

initialize this value but we don't see

our destructure is called what is going

let's investigate this a little more the

reason is we are not explicitly

releasing this memory here through the

base pointer let's do that we're going

to delete p base here and we're going to

run again we're going to weld with gcc

now our destructors should be called

we're going to run rooster and we are

going to see that the base cleanup

version was called and again this is

giving us static binding results you

don't want something like this so if you

get to this behavior i would advise not

to call the cleanup or setup functions

inside constructors or destructors and

that's the guideline i gave in the

slides you should really never call

virtual functions either from

constructors or disruptors especially if

you are doing this from a parent class

hoping to get the most specific virtual

function called through polymorphism if

you want to do that the best thing you

can do is to call the cleanup functions

is to call the setup and cleanup

functions after your object has been

properly constructed or before your

object gets to be destroyed so what you

can do here is call the setup method on

the pbes pointer here let's do that and

we're going to call setup this is going

to call our virtual function and we are

going to get polymorphic behavior this

is going to print a 100 as we expect

the derived version of setup here and

before we delete our object we will need

to call the cleanup function if we need

to do some custom cleanup here so i'm

base and call the cleanup function and

this is going to give us the behavior we

want we're going to build our program

pass this through gcc the both is going

and run rooster and we are going to see

that this constructor was called derived

constructor was called we will call the

derived version of setup our value will

be 100 and when we get to release or

clean up our memory the derived version

of cleanup will be called and then we

will destroy the derived part of us and

then we will destroy the base part of us

this is going to work in line with the

behavior we are familiar with with

polymorphism and this is really cool so

this is what you should do you should

never call virtual functions from

distractors and constructors because

that's going to give you static binding

results and what you want in this case

dynamic binding behavior this is really

all i have to share in this lecture i

hope you found it interesting we are

going to stop here in this one the next

one we're going to learn about the type

id operator that can come in handy

especially if you want to debug

polymorphic code in your c plus plus

program go ahead and finish up here and

meet me there in this lecture we're

going to learn about pure virtual

functions and abstract classes and pure

virtual functions are a mechanism we

to mean that the method isn't meant to

here we have a simple inheritance

hierarchy to try and drive this home the

base class is shape and we are deriving

from this class to create a circle class

and on the other side we are deriving to

create a rectangle class if we look in

the shape class we have two virtual

methods one is going to be used to

compute the perimeter of the shape

the other is going to be used to compute

the surface of the shape but if we go

down in our inheritance classes we're

going to see that we have the same

methods these are going to be overrides

of what we have in the base class

but the special thing about this

is that we don't have implementations

for these methods in the base class here

and this is by design if you think about

it this is an abstract shape we don't

know if it's a rectangle we don't know

if it's a circle we don't know if it is

a triangle so we don't really have

concrete information we can use

to properly compute its perimeter and

its surface so it makes sense to really

leave in the declaration for these

methods but leave the implementation

details to inheriting classes because

these classes are going to have concrete

information we can use to reliably

compute the perimeter and the surface

and we can get this information here

so in c plus plus we mean this kind of

design by setting up these methods as

and what this is going to tell the

compiler is these methods are not meant

to be implemented in the base class they

overridden and implemented by

inheritance classes and another side

effect of this is that the compiler is

going to prevent you from creating

objects of this class because it really

doesn't make sense to create an object

if you want to be able to compute its

perimeter if you want to be able to

compute its surface so why bother

creating an object that you won't really

be using in your c plus plus program the

meaning for this base class is just to

be a an idea or a representation of a

shape without really going into the

concrete implementation of how that

hopefully this makes sense so let's see

how we can do this in code here we have

a simple class which is going to be our

shape class we are going to have two

virtual functions we're going to have

the perimeter function we're going to

have the surface function these are

going to be virtual functions or virtual

member functions i should say but we are

pure virtual functions by using the

syntax you see here so we're going to

prepare an echo zero and this is going

to tell the compiler that these are pure

virtual functions once you set up these

functions a few things are going to

happen in your class this class is going

to become an abstract class in that

you want to be able to create objects of

this class anymore if you try to do that

you will get a compiler error another

thing is that you don't need to put in

implementations for these methods

because you marked them as pure virtual

and what this means is that the

implementations will be put in by

inheriting downstream classes because

they will have concrete information to

compute the perimeter or the surface as

we have here so we don't need to bother

with definitions for these functions

here if you even try to put in a

definition here you're going to get a

compiler error because this is a virtual

function we have no business putting an

implementation in the base class here

these are meant to be implemented by

downstream inheritance classes okay once

we have our ship class and our

inheritance hierarchy we can try to run

this in our code for example if we try

and create a shape object we're going to

get a compiler error because shape is an

abstract class so we can't create

objects of it and i don't think i made

this super clear once you set up at

least one pure virtual function in your

class the class is automatically going

to become an abstract class and what

that means is that you want to be able

to create objects of this class so this

is an abstract class we have here and if

we try to create an object of it as we

are doing on this line here this is

going to give us a compiler error but we

can still use a base pointer to manage a

a common setup we do with polymorphism

so for example here we can set up a

shape pointer and use this to manage a

rectangle object if we call the surface

member function on our base pointer this

is going to do a polymorphic call and we

will get the surface of the rectangle

and we're going to print this out here

you're going to see that this is going

to work we can also use the base pointer

to manage a circle object as we see here

if we call the surface method this is

going to do polymorphism and it is going

to call the surface version of the

circle class and we can see it printed

out here this is the design we can

achieve even if shape is an abstract

class we can't create direct objects of

shape as we are doing here but we can

use a base pointer or a shape pointer to

manage derived object through

polymorphism and you need to be aware of

this okay now that you have an idea

about what a pure virtual function is

and what an abstract class is

let's see a few ideas you need to keep

in mind if your class has at least one

pure virtual function it will become an

abstract class you already know this you

can't create objects of an abstract

class if you try to do that you will get

a compiler error another thing i don't

think amid super clear is that derived

classes from an abstract class must

explicitly override all the pure virtual

functions from the base class

pure virtual class that you don't put in

an implementation in for your derived

class is also going to become an

abstract class and you want to be able

to create objects of that you need to

keep this in mind another thing you

can't do you can't call the pure virtual

from the constructor of the abstract

class if you do this you're going to get

a compiler error because we don't have

implementations for these things so this

is not going to work the constructor of

our abstract class is used by deriving

classes to build the base part of our

derived objects but they are not meant

to be used from the outside because we

can't really create an object of an

abstract class so now that you notice

we're going to head over to visual

studio code and play with this a little

more here we are in our working folder

the current project is pure virtual

functions and abstract classes we are

going to grab our template files and put

them in place and we're going to paste

them in this project here and we are

going to grab the files that make up our

inheritance hierarchy you are going to

get these files from the resource

section of the course if you want you

can download them and use them like i am

using them here or even better you can

type the code and see how these things

really work that's the best way to learn

i do recommend that but we want to save

on time here so i am just going to reuse

these glasses that i have lying on my

drive i am going to open this in visual

studio code by dragging and dropping

here we have our shape class here this

is going to be our base class you're

going to see that we have our member

variable which is going to be the

description for our shape we have a

bunch of constructors here but the most

important thing here is that we have a

bunch of pure virtual functions here and

if you go in the cpp file you're going

implementations then for the perimeter

and surface functions these are pure

virtual functions and we have no

business putting in an implementation in

the base class once we have these

virtual functions in and mark them as

pure virtual functions by prepending n

equals zero here this class here is

going to become an abstract class and

what that means is that we can't create

objects of this class it is meant ready

to be inherited from and downstream

inheritance classes are going to be

override these methods here otherwise

they are themselves going to become

abstract classes we're going to have a

chance to look at this here we also have

our rectangle class which is going to be

inheriting from shape it is going to

override our two methods we're going to

override the perimeter function we're

going to override the surface function

for rectangle the perimeter is computed

this way we're going to multiply

the width by two and the height by two

and we're going to add these two things

up we're going to compute the surface by

multiplying width and height and this is

going to give us the data we want we can

look at circle it is going to also

inherit from shape and it is going to

override our methods here if we want we

can even put in a radius and a variable

to keep track of pi we can do this you

can really do this however you want this

is just going to allow us to compute the

surface relatively easily in this class

here let's look at the implementation

nothing special here this is just going

to forward the construction of the base

base constructor and this is going to do

whatever it is we want to do here let's

head over to the main cpp file and

we are going to include circle and

rectangle let's do that circle dot h and

we're going to put in rectangle that h

and we're going to first try and create

a shape object let's do that we're going

to say shape and say shape pointer and

this is going to be new shape we can use

a default constructor and if we do

something like this you're going to see

that we're going to have a compiler

error here we have a squiggly line but

if we bring up a terminal window and

look at the problems tab we're going to

see that object of abstract class type

shape is not allowed so shape is an

and why is it an abstract class because

we have an at least one pure virtual

function here we actually have two and

this is going to make our shape class an

abstract class what that means is that

we can't create objects of this class

and if we do that we're going to get a

compiler error let's try and build this

program we're going to pass this through

gcc our favorite compiler we are going

to see that the bolt is going to fail

we're going to have a bunch of errors if

we go up and look at the error we have

invalid new expression of abstract class

so we can't really create an object of

this let's go down and see what these

errors are saying note because the

following virtual functions are pure

within shape and they are going to try

and really be helpful in the errors that

they give here and all they are saying

is that we can't create objects of this

class because we have pure virtual

functions inside okay now you know this

if a class is abstract you can't create

objects of that class but you can still

use a base pointer to manage derived

objects of that class so let's comment

this out because this is going to make

our code not compile and we're going to

say that this is going to give us a

compiler error and we're going to try

and use the base pointer to manage a

rectangle object we can do this so we're

going to set up a shape pointer and it

is going to be managing the memory of a

rectangle object we're going to go

through the base pointer and call the

surface method and this is going to call

the implementation in rectangle because

our base pointer is really managing the

rectangle object if you want you can

even use the type id operator to print

the dynamic type of this shape rect

pointer you're going to see that it is

managing a rectangle you can actually do

this because we learned about that in

the last lecture so let's practice that

we're going to say dynamic type of shape

wrap and we're going to say type id and

we're going to de-reference the pointer

we're going to say shipwrecked and we're

going to print the name of this and

we're going to see it print out on our

powershell window and after this we are

going to print the surface that we got

from this call here and we're going to

see what this gives us let's try and

build this program we're going to pass

it through gcc our favorite compiler the

bullet is going to be good we're going

to clear and run rooster we're going to

see that the dynamic type is rectangle

you can see that right here so the base

pointer is really managing a rectangle

object and this is what we have here and

if we call the surface method we will be

calling the method on the dynamic type

so we will be calling this surface

method on the rectangle class and we

using the implementation we have here so

the surface function that is going to be

called is what we have on line 20 in

rectangle here and this is going to just

be a multiplication of width and height

and we're going to get 100 here because

our width and height happen to be

10 and 10 so multiplying this is going

to give us 100 as we see here this is

really cool this is what we expect we

can even use our base pointer to manage

a circle object so let's do that we're

going to put in a separator to be able

to follow this easily and our output so

let's say stdndl here and we're going to

put in the code so we're going to set up

a base pointer which is really going to

be managing a circle object here and we

will call our surface method this is

polymorphically because surface is a

so we will get polymorphism here and we

will call the surface method on the

circle object which is really our

dynamic type if we print this out we're

going to see the surface printed out but

if we want we can even print the dynamic

base pointer here so we're going to do

the same thing we did for rectangle we

can use our type id operator to print

the dynamic type of shape circle and

we're going to say shape circle here and

this is going to do what we want let's

look at this we're going to be printing

the surface here this is exactly what we

want so let's build and run we're going

to pass this through gcc the bolt is

going to go through as you see here if

and run rooster we're going to see that

the dynamic type is now a circle so the

base pointer or the shape pointer we

have here is really managing

a circle object polymorphically so if we

call a virtual function on this base

pointer it is going to call

specific implementation of the surface

object we have and that happens to be

for this circle object here this is what

if we compute the surface we're going to

see that it is going to be using the

data we have here and we will get this

number as our surface if you plug this

in you're going to see that this is

really right so this is really all i had

to share in this lecture we can set up

pure virtual functions in a base class

and what that's going to do it is going

to make our class an abstract class but

we want also be able to put in

methods anymore in the base class

because they are meant to be

overwritten and implemented by

downstream inheritance classes so if you

go in here and try to put in an

implementation we will probably get a

compiler error because this is not

allowed you see we have a problem here

if we try to build we will get a weird

compiler error let's make sure we see

the compiler error so world finished

with errors and we are going to see

what's the problem here let's go up and

pure specifier on function definition so

this is not allowed so we are really

conflicting ourselves here we are

marking this function as a pure virtual

and what that means and a pure virtual

functions isn't meant to have a

definition but we are also putting in a

definition here so the compiler is going

to be confused this is not something we

should be doing another thing i want to

point out before we wrap up this lecture

downstream inheriting classes are forced

to override and implement all the pure

virtual functions from the class that

they inherit from if they don't do that

they are themselves going to become

abstract and we want to be able to

create objects of them so let's try and

for example comment out the surface

implementation here and that's going to

make our circle class an abstract class

and if we try to create an object with

circle we will get a compiler error

because now circle is an abstract class

let's try and build and show you the

compiler error and this can really be

confusing if you are a beginner on this

you will be wondering why you can't

create objects of your class even if you

didn't really explicitly put in any pure

virtual function the reason is we are

inheriting from an abstract class that

has two pure virtual functions but we

are only overriding one pure virtual

function we need to override all of them

otherwise our class is also going to be

an abstract class let's look at the

compiler error we are getting here let's

go up and see if we can find it we are

going to say in function in main

evaluate new expression of abstract

class type circle we are trying to

create an object from an abstract class

this is the error we have here and you

so let's go back and make sure we are

overriding all these stunts because we

need to do that to be able to create

objects of a circle and now this is

going to work exactly as it should let's

build and make sure of that the bullet

is going to be good we are fine this is

working exactly as we want this is

really all i wanted you to see in this

lecture i hope you found it interesting

we are going to stop here in this one

the next one we're going to learn about

interfaces in c plus plus and they are

going to be reusing the knowledge we

learned about in this lecture go ahead

and finish up here and meet me there in

this lecture we're going to see that we

can model interfaces in c plus plus

and now there's a lot of things that

might not make sense in what i just said

so let's break this apart an interface

can be thought of as an abstract class

with only pure virtual functions and no

member variable so if you have a setup

like that you can call that thing an

interface let's look at a simple example

here here we have a simple class called

stream insertable you see that it

doesn't have any member variable it only

has a pure virtual function here and a

helper function that we could set up to

help us do a few things the only

specification to make this an interface

is to have in only pure virtual

functions and no member variables if you

have in a member variable this is going

to stop becoming an interface in c plus

plus okay so you can think of an

interface as an abstract class

with at least one pure virtual function

and no member variable that's going to

make it an interface down here you see

that an interface can be thought of as a

specification of something that will be

fully implemented in a derived class

but the specification itself is going to

reside in the abstract class another way

to think about an interface is to treat

you can attach to your types to give

them superpowers for example this stream

has a single job and that's going to

allow our types to insert data into

output streams like sddc out this is the

only thing this interface is going to

add to our times so we can take this

interface and attach that to a point

class for example and we will

automatically be able to print point

objects to the output stream and we want

to need to overload the stream output

operator in the point class we can do

the same thing to our bird class we can

do the same thing to our dog class and

we will be able to print these things

without having to overload the stream

output operator hopefully you can see

how powerful this is if we manage to set

up this kind of relationship between our

type and our interfaces so again an

interface is something you can attach to

your types to give them powers or

features that they originally didn't

have and that's going to save you from

having to implement these features

separately in each class for real time

so this is a huge time saver now you

must be asking how do i take my

interface and attach it to my type well

the way c plus plus does this you have

to inherit from the interface from your

type to attach the interface to your

type so for example if we wanted to

attach this interface to our point class

what we would do is something like this

we would set up our point class

and inherit from our interface which is

stream insertable the moment we do this

our point is going to be able to print

thanks to the console through the stream

output operator but hopefully you can

see that something is missing how does

our point class know how to print stuff

if we go up and look at our stream

insertable interface we're going to see

that it is declaring a stream output

operator it is this thing that is used

to print data to the output stream you

see this is a regular output stream

operator we will be printing to sddo

stream and the object is named out here

and we will be printing whatever operand

that is passed as a second parameter

we will need to set up a virtual

that will need to be implemented by

whoever inherits from our interface here

and this is going to be super powerful

we are going to take over the job to

print to the output stream but we will

let inheriting download classes to

specify what we print and they are going

to specify that in this virtual method

let's look at our point class again and

really put the puzzles together here and

understand how this works okay this is

our point class and it is going to be

inheriting from our interface and it is

going to implement our virtual function

here we are going to set it up here and

we are going to mark it as an override

because it is overriding a method that

comes from our stream insertable

interface here and it is going to

specify which data we print to the

output stream and how the data is going

to be printed out you can specify

these things here we're going to format

the data in a point and we're going to

be using these square brackets to put mx

and my here and notice that this is an

override so the inheritance class has

all the information we need to put in

our output stream operator and we will

do that through our stream insert

override here now let's go back to our

stream insertable interface to see how

our output stream operator actually

works what we have here is what would be

a header and this is going to just put

in a declaration for this but we can

even look at its implementation the

implementation for our output stream

operator may look something like this we

are going to pass in the first operand

and the second operand here but notice

what we are doing here we are going to

the stream insert virtual function on

our operand here and this is going to

the most specific implementation we can

find for the stream insert if we are

trying to print a circle for example

this is going to call the stream insert

override on a circle object if we are

trying to print a point this is going to

call this method on our point object and

this is going to use polymorphism

because our second operand here is pass

by reference hopefully you can see how

this is super powerful i know this is

convoluted because we are jumping around

trying to explain this but i couldn't

really come up with an easier way to put

this we have to try this encode to

really see the power of this but this is

really the power of interfaces we can

design our features and wrap them in an

interface and we can really attach that

interface to any type we have in our c

plus plus program and that type is going

to automatically inherit the features

that we have set up in our interface for

example now that we have attached this

interface to our point here we can print

our points on the output stream and this

is going to work automatically you see

that we don't need to set up an output

stream operator on our class altogether

we can even go further and attach this

interface to a full inheritance

hierarchy for example if we have our

base class to be animal and we inherit

from this class to create all kinds of

crazy classes we can go on and attach

our interface to the base class here and

this is going to make all our classes in

our inheritance hierarchy have the

features that the interface has brought

to the base class so for example we can

attach our interface to the animal class

by inheriting from stream insertable

here and this is going to give our

animal the powers to be printed out to

output streams and this is going to be

powered by the virtual function that we

we are going to specify which data to

print in our animal class and how the

data is going to be printed out here and

we can do that in this override and this

is super powerful once we do this we're

going to go to each class in our

inheritance hierarchy and implement the

override because if we don't do that

this class is also going to become an

abstract class because it is inheriting

from a class that has a pure virtual

function remember if you inherit from a

class that has at least one pure virtual

function you will be forced to implement

all the pure virtual functions that come

from your parent class if you don't do

that you are going to become an abstract

class yourself and we don't really want

that that's why we are overriding the

stream insert override here and with

this we are going to specify which

information to print from our object

here and here we are going to put out

the description and the wing color and

this is the format we specify here and

this method is going to be called by our

output stream operator which is coming

from our stream insertable interface

hopefully you can see how this is super

powerful okay now that you know this

we're going to head over to visual

studio code and play with us a little

more here we are in our working folder

the current project is abstract classes

as interfaces we're going to grab our

template files and put the data in place

and i'm going to copy this and put that

we are going to put in the files we're

going to be using in our inheritance

hierarchy you see we have our animal

hierarchy here you can grab these files

from the resource section of this

lecture and you can reuse them like we

are using here or if you want you can

even type this but i don't really

recommend this because this is too much

typing we just want to learn about

interfaces here and that's what you

should focus on so we're going to open

this up in videos video code and this is

going to give us all the files we need

we're going to look at the top class and

we will see that it is inheriting from

our stream insertable interface so let's

look at our stream insertable interface

because this is the focus of this

lecture here so it is a regular class as

you see here it is class stream

insertable we're going to set up an

output stream operator and it is really

like any other output stream operator

you have seen we're going to pass the

and we are going to specify our pure

virtual function which is going to be

implemented by downstream inheriting

classes from this class here and this is

going to set up polymorphism and what

is if we call this method on our second

operand here we are going to call this

method polymorphically so if you are

trying to print a point we are going to

call this method on a point object and

we will print it out exactly how the

point wants to be printed if we are

printing a circle we will call this

stream insert method on the circle and

we will print a circle exactly how a

circle wants to be printed out let's

look at the implementation and it is

nothing really complicated we're going

to specify our output stream object as

the first parameter here and the second

parameter is what we want to print out

we will pass this by reference and this

is going to allow us to do polymorphism

remember that stream insertable is

really going to become our top base

class so we will basically be setting up

stream insertable polymorphism here you

need to keep this in mind we are going

to call our stream insert method on our

operand and we're going to pass the

stream output we want to print on and

we're going to return this output stream

like a regular output stream operator to

allow output chaining in our operator

here once we have this stream insertable

interface we can really use it however

we want let's head over to the main cpp

file and try to play with us so what we

are going to do is crack this open and

we are going to remove whatever it is we

don't need we are going to include our

interface so we're going to include

stream insertable let's do that

insertable.h i think this is the name

and we're going to set up a point class

which we wish to be printed out on the

output stream notice that we want to

inherit from stream insertable and what

this is really doing is attaching the

interface to the point class here and

because this stream insertable

interface has a pure virtual function

override this pure virtual function here

if we don't we want to be able to create

objects of our point here let's go down

and show you that we're going to get

that problem if we don't do that we're

and say p1 and for example put in 10 and

we will have a compiler error because

now the point class is an abstract class

because it is inherited from a class

that has a pure virtual function and it

is not overriding that pure virtual

so in other words this class still has a

non-implemented pure virtual function

an abstract class and we can't create an

object of it if we're trying to run this

code we're going to pass this through

gcc we will get a compiler okay we have

a compiler error here and we need to fix

this all we need to do is to implement

the interface that comes from our stream

insertable interface here so we can grab

our pure virtual function and implement

it in our main cpp file for the point

class we're going to put it in here and

we will remove the pure virtual function

specifier here and we will put in an

implementation we want to specify that

this is an override of a method that is

coming from our upstream parent class

and we are going to head over in the

body of our function and put in the

information we want to put out

this is a point object so we just want

to print the m x coordinate and the m y

coordinate here and this is the format

that we want and at this moment the job

of this function is really done

and it will be picked up polymorphically

if somebody tries to call this on a

point object through polymorphism and

this is going to work now that we have

this point we can try and build and make

sure this is working let's make sure we

don't have the compiler error anymore

the world finished successfully so we

are cool here but what we want to see is

point objects because that's the whole

point of attaching this interface to our

point class here so what we are going to

do is print this out we're going to say

sddc out we're going to say p1 and we're

going to say p1 here this is how we

would use our output stream operator you

see we don't have a compiler error this

is really magic some of you are going to

ask how is this even working somebody is

going to look at your class they are

going to look you don't have an output

stream operator but you can print your

objects so how is this working well this

is working through the magic of

interfaces we are attaching this

interface to our point class and this is

going to give our class the powers that

come from this interface and one of

those powers is to use the output stream

operator we get from this interface we

can use that directly and what this is

going to do let's look at the

implementation of this interface this is

going to just call the stream insert

virtual method on the object that we

pass as a second parameter in this

operator here and the second parameter

happens to be the point that we are

printing here so what this is really

is something like this we're going to

try and figure out what the compiler is

going to try and do we are going to say

p1 and we're going to say operator

stream output and we're going to say

stdc out that's the stream we want to be

and the point we want to print is p1

this is basically what the compiler is

going to do and it is going to print our

thumb and this method is available in

our stream insertable header and it is a

friend of our interface that's why we

are able to do something like this

accessing the data from our interface

let's build and actually show you that

this is going to work we're going to

pass this through our gcc compiler the

build is going to be good so we can

clear not clear we're going to control z

on this and we're going to bring up a

powershell window and we're going to

clear this time and run rooster you see

that we are creating our point here and

this is really cool we can even

uncomment this and we're going to use

sddc out because the compiler is going

to take this and turn that into this and

we have the ability to have code that is

much more readable by c plus plus

developers out there we're going to

build and run this again the build is

going to be good we can clear and run

rooster and this is going to print our

point here this is really cool but this

is not the end of our store we can even

print an entire inheritance hierarchy

look at what we did at our animal class

here we attached this interface to our

animal class and the moment we do that

we need to override the pure virtual

that comes with this interface and

that's what we did down here we have

overwritten the stream insert

and in the body we're going to specify

which data we want to print and how to

print that data that's the whole point

of this override we are doing here we

are going to do the same thing in each

inheritance class from animal for

example if we go to feline we're going

to do exactly the same thing we are

going to inherit from animal and this

will indirectly inherit from our

the pure virtual function that comes

with that interface and we do that here

we're going to specify which data we

want to print in this case we're going

to put the description out and the first

style and we are going to specify the

format in which we want the data to be

printed out again that's the whole point

of overriding this virtual function here

we're going to do the same thing on each

inheritance class in our inheritance

hierarchy for example we did the exact

we did the exact same thing for a cat

and we're going to do the same thing on

our bird classes that's exactly what we

do here specify which data to print out

and how the data is going to be printed

out and this stream insert override is

going to be picked up by our interface

when we get to call the output stream

operator here notice that we are calling

this thing polymorphically we are

method on a reference that we pass here

and this is going to resolve this using

dynamic binding this is going to work

really well now that we have this setup

we can head over to the main cpp file

and really do all kinds of crazy things

let's put in a separator here and we are

play with us we are going to include the

classes we need to set up our animals

and we are going to put them in here we

have animal feline dog cat bird pigeon

and crow the moment we do this we don't

need to put in this stream insertable

because it is coming in directly from

this but we don't need to worry about

this because we have include guards in

but we are going to be using smart

pointers so let's include the memory

header and we can set up an animal and

try to print it out we will be using

polymorphism so we will go through a

base pointer to animal and use that to

manage a dog object here we are just

going to pass in the data and we will

try to print this animal out notice that

we are going through a base pointer

calling the output stream operator so

polymorphically and it is going to print

this information at the dog level and

what i mean by that is that if we go in

dog we're going to find our stream

insert that's going to print this

like we want to print a dog and this is

super powerful hopefully you can see how

cool this is we're going to try and

build this program we're going to pass

this through gcc the boat is going to be

good we can clear and run rooster we're

going to see that we print this as a dog

even if we used a base pointer to try

and print this out how cool is this we

can even use this to set up a bird and

print it out we're going to set up a

base pointer that is going to be

managing a bird you can see that we are

using a unique pointer here you can

really use any kind of smart pointer you

want we're going to print this out and

this will be printed out like a bird

wants to be printed out and that's going

the override from our bird class and

that's going to say bird is going to put

out the description it's going to put

out the wing color and this is really

going to work really well we're going to

pass this through gcc again the world is

going to be good we can clear and run

rooster you see that we are printing out

bird here and this is using polymorphism

combined with interfaces and this can

come in handy if this helps your

application depending on what you want

to achieve with zipclose plus we can

even put our animal data in an array and

try to print that out so we're going to

put out a separator to be able to follow

this nicely in our output terminal this

is going to do and we're going to go

down and put in the code to play with us

we're going to share an array of shared

pointers this is how we do this and

we're going to initialize this with all

kinds of crazy animals we're going to

put in a dog we're going to put in a cat

we're going to put in a crow and a

pigeon and we will be managing this

through base pointers notice that this

is an array of base pointers

and we're going to be calling the output

stream operator polymorphically so for

the first element here we will print a

dog how a dog wants to be printed out so

we will be using the stream insert

override from the dog class if we go

there we're going to see that we're

going to prefix our data with dog if we

hit the second element we're going to

print this like a cat wants to be

printed down the third element is going

to be printed out as a crow the fourth

element is going to be printed out as a

pigeon and this is going to fall in and

right away down here you see that we are

looping calling our output stream

operator and this is going to work

really well let's try and build this

program we're going to pass this through

gcc the build is going to be good so we

can clear and run rooster and you're

going to see that we are printing our

information here the first thing is a

dog the second thing is a cat the third

thing is a crew the fourth fan is a

pigeon and this is working really well

hopefully you can see how interfaces can

be powerful in your c plus plus design

use this if it makes sense for whatever

application you are designing with z

plus plus my main goal here is to

introduce you to the idea of interfaces

and how powerful they can be again an

interface is something you can attach to

and at the moment you attach that

interface to your type your type is

going to have the powers that come with

that interface and all you need to do in

your deriving classes is to implement

the virtual functions that come with

that interface and the interface will

pick them up and use them to do whatever

polymorphically and that's going to be

really cool we are going to stop here in

this lecture this one we're going to try

and recap what we saw in this chapter

go ahead and finish up here and meet me