Original subtitles

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Hey, guys, welcome to the final project of today, and in this final project, we're going to be building

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a tip calculator.

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So the final output is going to look like this.

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It's going to print

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Welcome to the tip calculator.

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And it's going to ask you for an input for how much the total bill came to.

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Let's say that we and a couple of friends went out for lunch and it came to 124.

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56 dollars.

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And then it'll ask you, what percentage tip would you like to give?

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So let's say we want to give a 12 percent tip.

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So we enter 12 and hit enter.

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And then finally it asks how many people are splitting this bill?

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Let's say there's seven of us and then hit enter.

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Finally, it's going to tell us that each person should pay about $19.93.

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Notice how the final bill, even though after all of these calculations, it's probably got more numbers

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after the decimal point, we only want two decimal places of accuracy, so it should be rounded to two

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decimal places.

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The second thing to remember is that these are percentages, and in order to calculate a percentage of

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something, you can multiply a number by the percentage number divided by 100.

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Let me show you this in a little bit more detail.

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If you head over to replit/appbrewery/tip-calculator-start, then you've got

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these starting file for this project.

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And here I just want to quickly show you how the math works, because this project is not about testing

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your math.

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It's about seeing how well you've understood the programming concepts.

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Let's say that we had a bill of $150.

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If we were to apply a 12% tip on top of that, then 12% is going to be equal to twelve

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divided by a hundred, which is equal to 0.12.

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Now the next step is we can multiply 150, the total bill, by 0.12.

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And this will give us what 12 percent of 150 is, which is 18.

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Now we of course, have to add the tip onto the final bill so it becomes 150 plus 18.

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So $150 with a 12 percent tip is equal to $168.

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Now, a shorthand way of doing all of this is simply multiplying 150 by 1.12.

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So the 1 is 150, and then it's 0.12 on top of that.

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So when we do this, it gives us pretty much the same number.

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Now, if during your testing and your coding you come across some sort of number that looks a little

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bit strange because you think 150 multiplied by 1.12 should actually equal 168

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precisely.

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So what are all of these extra numbers at the end?

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Now, the short answer is you don't have to worry about it.

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It's simply related to how Python processes these floating-point numbers.

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If you're really interested and you want to read about this, then I'll link to this page in the Python

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documentation where they tell you why this is happening.

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But be warned, it's pretty dense and it's pretty heavy.

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But the final conclusion is it's just the way that Python is approximating this number.

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So you don't actually have to worry about this.

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Now, once we've gotten to 168, the next step is to split it between five people.

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So 168 divided by 5 is equal to 33.6.

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Now, what we want to show the user is we want to show them the amount that they have to pay with two

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decimal places of accuracy.

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We want to say something like 33.60 if this is the case, because that's normally

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how we represent numbers when it comes to money.

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So what I want you to do is to also be able to round any of these numbers to two decimal places.

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If you have successfully created this program, then it should work exactly as this example version

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would, which you can find if you go to tip-calculator-end.appbrewery.repl.run, and

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you'll be to see the formatting where it actually tells you each person should pay this particular dollar

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amount and it's rounded to two decimal places.

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And this is the amount after taking into consideration these three different inputs from the user.

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Have a play around with the final product and then have a think about how you would create this program

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step by step and then give it a go by forking this starting repository to your own account and then

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try to achieve this result.

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This is going to test everything that you've done so far including fstrings, including complex

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mathematical operations,

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including PEMDAS and calculating numbers and the order in which mathematical operations are run by

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a computer, as well as everything you learn in the previous lesson and the previous days as well. I think

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this is going to be a lot of fun and the end result is going to be kind of useful the next time that

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you need to split the bill between friends.

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So I'm going to let you pause the video and get on with it.

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And then once you're done, if you want to, head back over here and I'll walk through the solution with

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you. But I really recommend you giving it a good go before you come back.

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So pause the video now and I'll see you later.

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OK, so we've seen how the program is supposed to work and we're trying to create it from scratch by

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reverse-engineering it essentially. The first thing I'm going to do is I'm going to fork the starting

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project and create my own version of it which I can edit.

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Now, the first thing our program should say is welcome to the tip calculator.

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So that's easy enough.

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We just have to create a print statement.

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Perfect.

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And if you're creating a really enthusiastic tip calculator, you can replace the full stop with an

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exclamation mark.

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OK, so let's run it step by step to make sure that we don't have any errors along the way.

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So the first step seems to be working. Now

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the next step is to ask the user for some input.

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And we want to know what was their total bill, what did it come to?

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So let's go ahead and create an input and ask them what was the total bill?

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And then we'll add a dollar sign or whatever currency it is that you prefer to work with.

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Because when we actually run this, you'll see that the input will go straight after the end of that

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string,

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so at the dollar sign.

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So now we can enter a dollar amount like this, but it's not really saved anywhere.

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This data just disappears because we haven't stored it inside a variable.

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So let's go ahead and do that.

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Let's call this variable bill and we'll set it to equal whatever the user typed in to this input.

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Now, remember that this bill is going to have a data type of a string, right?

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So if I go ahead and hit run and let's just type some numbers in here, you'll see that the data type

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of the bill is, as we said, a string. In order to be able to do math,

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you might remember, we have to change this into a number format,

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so a float or an int.

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Now, in this case, because the bill is likely to have numbers after the decimal place, it's probably

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better that we turn it into a float so that we get the most accurate result possible. Now that we're

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done with the bill,

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the next question the tip calculator should ask is what percentage tip would you like to give? 10, 12

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or 15?

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Or you can, of course, switch this up depending on how much tip you normally give.

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So the next line is going to be another input.

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Here, I'm asking the user, how much tip would you like to give and giving them some examples. And

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notice how in my examples, I don't actually have the percentage sign here because I don't really

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want them to type the percent sign into this input because if they do when they say 12%,

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this is going to be really hard for me to turn the 12% into an actual number.

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So you could, in your input message, say something like how much tip would you like to give 10,

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12, 15?

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Please don't add any percentage signs.

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Just add the number or something like that.

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But again, once we've done this, it's not stored anywhere unless we add it into a variable.

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Now we've got a bill that stores the total bill as a float and we've got a tip which is going to be

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a whole number, 10, 12 or 15,

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right?

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So depending on what you think is best, you can either turn this into a float or in my case, I'm probably

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going to convert it into an integer.

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So now we're onto the final step, which is how many people to split the bill between.

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So let's go ahead and create a variable called people.

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And I'm going to add an int wrapper around this input so that even in the very beginning, we know that

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we have to convert the number of people into a whole number because I've never had a meal with

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3.5 before.

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So the input is going to be how many people to split the bill.

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And at this point, they should enter the number of people which will turn into an integer stored inside

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this variable called people. So now that we've got all the data collected from the user, we're finally

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ready to do some math.

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And we said that the way to work out the tip is by multiplying it by 1. and then the number after

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the decimal point is whatever percentage they decided to give.

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So it would be 1.1 if it was 10 percent and 1.15 if it was 15 percent.

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Let's go ahead and calculate the bill_with_tip.

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So remember how we said that before the tip percentage is equal to the whole number, 10, 12 or 15,

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divided by 100, which turns it into 0.1, 0.12 or 0.15,

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and then once this calculation is done, we can multiply it by the bill. And then finally we add that

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to the original bill.

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So let's go ahead and print this and just check to see that it looks sensible.

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So bill_with_tip is what we're going to print.

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And let's put some easy numbers in there.

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And let's say that the bill was a hundred dollars and the tip was 10 percent.

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So then the 10% of hundred dollars is ten dollars.

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So the bill_with_tip,

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that's what's going to be printed next, should be 110. So we can type anything in here because

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we're not using it.

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And you can see that this calculation, bill_with_tip, is 110, which is what we want.

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Now, there's a lot of other ways that you can express this.

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For example, you could say, bill * (1 + tip/100).

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So this would actually give you the same result as well.

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But remember what we said previously about how Python is a little bit weird with floating-point numbers.

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But essentially this is still giving us the same result, which is 110.

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So you can choose whichever way you find most intuitive.

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And if you want, you can even split this up into several steps, right?

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We could say that tip_as_percent is equal to tip/100.

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And then we can multiply the bill by the tip_as_percent to get the total tip amount.

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And then finally, we can get the total bill by adding the bill to the total_tip_amount.

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Feel free to do this whichever way makes sense to you, but I'm going to leave it with as many steps

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as possible so that you can actually work through the logic if you got stuck on this math.

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Now, the next thing we need to do is to divide the total bill by the number of people.

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So if we had five people, then we would divide it five ways,

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right?

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So let's call this bill_per_

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person, which is going to be equal to the total bill divided by the number of people.

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Now, at this stage, this bill_per_person is a floating-point number, so it could have many, many

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digits after the decimal point.

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If we want to round this to two decimal places, then you might remember from some of the lessons today,

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we have access to a function called round.

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And here we can add the number that we want around, which is the bill_per_person,

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and then after a comma, we can specify how precise, how many numbers or how many decimal places do

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we want to round this bill to.

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And in our case, it's two decimal places.

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So now this is the final amounts, which I'll call final_amount which is the bill_per_person rounded

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to two decimal places.

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And we can now finally print this to the user and say each person should pay...

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And remember, you can either use string concatenation which will require you to convert this number

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into a string again, or use the trick that we learned in the previous lessons where we can create an

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fstring by adding F in front of the string and then using some curly braces to insert the final amount

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right here.

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And we can write the final_amount dollars or we can put a dollar sign in front and maybe a colon here.

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And now if we clear our console and run our code, then you'll see it work.

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So welcome to the tip calculator.

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What was the total bill?

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Let's make up some random number.

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What percentage tip?

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Let's say we're going to get 15 and then we're splitting it between five people. And it calculates everything,

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doing all of that maths.

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And finally, it rounds it to two decimal places, giving us the final amount each person should pay.

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But what if we test it out with the initial numbers?

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Let's hit, run and let's try to put in 150 dollars as the total bill, and then we're going to give

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a 12 percent tip and we're going to split it between five people.

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Notice that is telling us that each person should pay $33.6.

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But normally, we're used to seeing that rounded to two decimal places.

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But we have that round function here already.

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So why is it not doing its job?

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Well, if you think about it, the result of this calculation is just 33.6. There's

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nothing after the six, but we want it to display a zero. And this is a formating problem rather than

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a mathematical rounding problem.

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So what do we do?

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Well, we go to our good friend Google whenever we're stuck and we're going to search for how to round

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number to two decimal places in Python.

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And if we take a look at the first Stack Overflow question, you can see that this person had pretty much

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the same problem that we had.

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And if we're scrolling down, you can see that the solution is to use some sort of formatting. And we

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can try out each of these examples one by one in code to see how they work,

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and we can also take a look at the documentation that they link to.

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So the actual way that we do this is by using a colon and then dot and then we specify that after the

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dot, we want two decimal points in our float. And we use the format function to do this.

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So instead of using round, we can create this final amount variable by creating a string using that

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format, :.2f, and then we can use the format function to pass in that bill_per_person.

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And now when we run this again, using the same inputs, we now get a .60 at the very end

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and this is basically turned this bill_per_person, which is a float into a string.

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And that string is abiding by this particular format, which is the two decimal places.

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How did you get on with this project?

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Did you manage to get it in one go without having to look at the solution? If you got stuck at any point

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or if your code didn't work as you expect it to,

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this is a time to go back to it, fix it, and make sure that you've understood everything that's been

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covered through this exercise.

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But if you already created it and it's working perfectly, then you're ready to go out there with your

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tip calculator in hand.

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Remember that you can save the URL of your tip calculator in your phone as a bookmark.

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So the next time you go out and have dinner or lunch with friends, then you can crack open your own

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tip calculator and figure out the final bill.

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So I hope you had fun building this project and doing all of the coding exercises and learning about mathematical

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operations, fstrings, data types, type conversion, and all of the things that we did today. Have a rest

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and I'll be back tomorrow teaching you about conditional statements and how we can get the program to

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do different things depending on certain conditions or certain parts of our code.

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So I bid you good night and I'll see you tomorrow.