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These are the user uploaded subtitles that are being translated: 1 00:00:00,150 --> 00:00:07,110 Hey, guys, welcome to the final project of today, and in this final project, we're going to be building 2 00:00:07,140 --> 00:00:08,730 a tip calculator. 3 00:00:09,390 --> 00:00:11,870 So the final output is going to look like this. 4 00:00:11,880 --> 00:00:12,760 It's going to print 5 00:00:12,810 --> 00:00:14,430 Welcome to the tip calculator. 6 00:00:14,700 --> 00:00:19,290 And it's going to ask you for an input for how much the total bill came to. 7 00:00:19,890 --> 00:00:27,360 Let's say that we and a couple of friends went out for lunch and it came to 124. 8 00:00:27,360 --> 00:00:28,920 56 dollars. 9 00:00:29,430 --> 00:00:33,580 And then it'll ask you, what percentage tip would you like to give? 10 00:00:33,600 --> 00:00:36,570 So let's say we want to give a 12 percent tip. 11 00:00:36,570 --> 00:00:38,570 So we enter 12 and hit enter. 12 00:00:39,210 --> 00:00:42,590 And then finally it asks how many people are splitting this bill? 13 00:00:42,600 --> 00:00:45,740 Let's say there's seven of us and then hit enter. 14 00:00:46,140 --> 00:00:51,270 Finally, it's going to tell us that each person should pay about $19.93. 15 00:00:52,230 --> 00:00:58,200 Notice how the final bill, even though after all of these calculations, it's probably got more numbers 16 00:00:58,200 --> 00:01:05,790 after the decimal point, we only want two decimal places of accuracy, so it should be rounded to two 17 00:01:05,790 --> 00:01:06,730 decimal places. 18 00:01:07,350 --> 00:01:14,430 The second thing to remember is that these are percentages, and in order to calculate a percentage of 19 00:01:14,430 --> 00:01:20,790 something, you can multiply a number by the percentage number divided by 100. 20 00:01:21,300 --> 00:01:24,020 Let me show you this in a little bit more detail. 21 00:01:24,480 --> 00:01:30,540 If you head over to replit/appbrewery/tip-calculator-start, then you've got 22 00:01:30,540 --> 00:01:33,420 these starting file for this project. 23 00:01:33,990 --> 00:01:39,720 And here I just want to quickly show you how the math works, because this project is not about testing 24 00:01:39,720 --> 00:01:40,230 your math. 25 00:01:40,230 --> 00:01:43,740 It's about seeing how well you've understood the programming concepts. 26 00:01:44,280 --> 00:01:48,810 Let's say that we had a bill of $150. 27 00:01:49,200 --> 00:01:57,690 If we were to apply a 12% tip on top of that, then 12% is going to be equal to twelve 28 00:01:57,690 --> 00:02:01,830 divided by a hundred, which is equal to 0.12. 29 00:02:02,670 --> 00:02:09,000 Now the next step is we can multiply 150, the total bill, by 0.12. 30 00:02:09,420 --> 00:02:14,470 And this will give us what 12 percent of 150 is, which is 18. 31 00:02:15,150 --> 00:02:21,390 Now we of course, have to add the tip onto the final bill so it becomes 150 plus 18. 32 00:02:21,930 --> 00:02:27,040 So $150 with a 12 percent tip is equal to $168. 33 00:02:27,540 --> 00:02:35,710 Now, a shorthand way of doing all of this is simply multiplying 150 by 1.12. 34 00:02:36,180 --> 00:02:42,580 So the 1 is 150, and then it's 0.12 on top of that. 35 00:02:43,110 --> 00:02:46,680 So when we do this, it gives us pretty much the same number. 36 00:02:47,490 --> 00:02:52,560 Now, if during your testing and your coding you come across some sort of number that looks a little 37 00:02:52,560 --> 00:02:58,860 bit strange because you think 150 multiplied by 1.12 should actually equal 168 38 00:02:58,860 --> 00:02:59,810 precisely. 39 00:03:00,210 --> 00:03:02,980 So what are all of these extra numbers at the end? 40 00:03:03,510 --> 00:03:06,540 Now, the short answer is you don't have to worry about it. 41 00:03:06,540 --> 00:03:11,940 It's simply related to how Python processes these floating-point numbers. 42 00:03:12,360 --> 00:03:18,420 If you're really interested and you want to read about this, then I'll link to this page in the Python 43 00:03:18,420 --> 00:03:21,660 documentation where they tell you why this is happening. 44 00:03:22,020 --> 00:03:24,750 But be warned, it's pretty dense and it's pretty heavy. 45 00:03:25,080 --> 00:03:30,170 But the final conclusion is it's just the way that Python is approximating this number. 46 00:03:30,480 --> 00:03:32,630 So you don't actually have to worry about this. 47 00:03:33,180 --> 00:03:38,610 Now, once we've gotten to 168, the next step is to split it between five people. 48 00:03:38,610 --> 00:03:44,970 So 168 divided by 5 is equal to 33.6. 49 00:03:45,570 --> 00:03:51,540 Now, what we want to show the user is we want to show them the amount that they have to pay with two 50 00:03:51,540 --> 00:03:52,950 decimal places of accuracy. 51 00:03:52,990 --> 00:03:57,630 We want to say something like 33.60 if this is the case, because that's normally 52 00:03:57,630 --> 00:04:00,880 how we represent numbers when it comes to money. 53 00:04:01,410 --> 00:04:07,740 So what I want you to do is to also be able to round any of these numbers to two decimal places. 54 00:04:08,610 --> 00:04:15,330 If you have successfully created this program, then it should work exactly as this example version 55 00:04:15,330 --> 00:04:22,290 would, which you can find if you go to tip-calculator-end.appbrewery.repl.run, and 56 00:04:22,290 --> 00:04:27,990 you'll be to see the formatting where it actually tells you each person should pay this particular dollar 57 00:04:27,990 --> 00:04:31,530 amount and it's rounded to two decimal places. 58 00:04:31,890 --> 00:04:38,520 And this is the amount after taking into consideration these three different inputs from the user. 59 00:04:39,090 --> 00:04:44,220 Have a play around with the final product and then have a think about how you would create this program 60 00:04:44,220 --> 00:04:50,610 step by step and then give it a go by forking this starting repository to your own account and then 61 00:04:50,610 --> 00:04:52,150 try to achieve this result. 62 00:04:53,040 --> 00:04:58,530 This is going to test everything that you've done so far including fstrings, including complex 63 00:04:58,530 --> 00:04:59,820 mathematical operations, 64 00:05:00,030 --> 00:05:07,320 including PEMDAS and calculating numbers and the order in which mathematical operations are run by 65 00:05:07,320 --> 00:05:13,440 a computer, as well as everything you learn in the previous lesson and the previous days as well. I think 66 00:05:13,440 --> 00:05:17,850 this is going to be a lot of fun and the end result is going to be kind of useful the next time that 67 00:05:17,850 --> 00:05:19,730 you need to split the bill between friends. 68 00:05:20,130 --> 00:05:22,320 So I'm going to let you pause the video and get on with it. 69 00:05:22,650 --> 00:05:27,330 And then once you're done, if you want to, head back over here and I'll walk through the solution with 70 00:05:27,330 --> 00:05:31,860 you. But I really recommend you giving it a good go before you come back. 71 00:05:32,100 --> 00:05:34,340 So pause the video now and I'll see you later. 72 00:05:40,000 --> 00:05:45,340 OK, so we've seen how the program is supposed to work and we're trying to create it from scratch by 73 00:05:45,340 --> 00:05:51,970 reverse-engineering it essentially. The first thing I'm going to do is I'm going to fork the starting 74 00:05:51,970 --> 00:05:55,510 project and create my own version of it which I can edit. 75 00:05:56,200 --> 00:05:59,960 Now, the first thing our program should say is welcome to the tip calculator. 76 00:06:00,250 --> 00:06:01,860 So that's easy enough. 77 00:06:01,870 --> 00:06:03,780 We just have to create a print statement. 78 00:06:04,330 --> 00:06:04,910 Perfect. 79 00:06:05,110 --> 00:06:10,360 And if you're creating a really enthusiastic tip calculator, you can replace the full stop with an 80 00:06:10,360 --> 00:06:11,290 exclamation mark. 81 00:06:12,100 --> 00:06:16,760 OK, so let's run it step by step to make sure that we don't have any errors along the way. 82 00:06:17,200 --> 00:06:20,170 So the first step seems to be working. Now 83 00:06:20,170 --> 00:06:23,170 the next step is to ask the user for some input. 84 00:06:23,470 --> 00:06:26,690 And we want to know what was their total bill, what did it come to? 85 00:06:27,280 --> 00:06:32,350 So let's go ahead and create an input and ask them what was the total bill? 86 00:06:32,980 --> 00:06:38,160 And then we'll add a dollar sign or whatever currency it is that you prefer to work with. 87 00:06:38,560 --> 00:06:45,040 Because when we actually run this, you'll see that the input will go straight after the end of that 88 00:06:45,040 --> 00:06:45,450 string, 89 00:06:45,460 --> 00:06:47,020 so at the dollar sign. 90 00:06:47,440 --> 00:06:52,250 So now we can enter a dollar amount like this, but it's not really saved anywhere. 91 00:06:52,270 --> 00:06:56,950 This data just disappears because we haven't stored it inside a variable. 92 00:06:57,400 --> 00:06:58,810 So let's go ahead and do that. 93 00:06:58,810 --> 00:07:05,650 Let's call this variable bill and we'll set it to equal whatever the user typed in to this input. 94 00:07:06,310 --> 00:07:14,320 Now, remember that this bill is going to have a data type of a string, right? 95 00:07:14,350 --> 00:07:21,010 So if I go ahead and hit run and let's just type some numbers in here, you'll see that the data type 96 00:07:21,010 --> 00:07:25,530 of the bill is, as we said, a string. In order to be able to do math, 97 00:07:25,930 --> 00:07:30,730 you might remember, we have to change this into a number format, 98 00:07:30,730 --> 00:07:32,420 so a float or an int. 99 00:07:32,860 --> 00:07:38,170 Now, in this case, because the bill is likely to have numbers after the decimal place, it's probably 100 00:07:38,170 --> 00:07:45,610 better that we turn it into a float so that we get the most accurate result possible. Now that we're 101 00:07:45,610 --> 00:07:46,980 done with the bill, 102 00:07:47,050 --> 00:07:53,980 the next question the tip calculator should ask is what percentage tip would you like to give? 10, 12 103 00:07:53,980 --> 00:07:54,730 or 15? 104 00:07:55,030 --> 00:07:59,050 Or you can, of course, switch this up depending on how much tip you normally give. 105 00:07:59,680 --> 00:08:02,800 So the next line is going to be another input. 106 00:08:04,910 --> 00:08:09,640 Here, I'm asking the user, how much tip would you like to give and giving them some examples. And 107 00:08:09,650 --> 00:08:16,040 notice how in my examples, I don't actually have the percentage sign here because I don't really 108 00:08:16,040 --> 00:08:24,770 want them to type the percent sign into this input because if they do when they say 12%, 109 00:08:25,250 --> 00:08:31,960 this is going to be really hard for me to turn the 12% into an actual number. 110 00:08:32,540 --> 00:08:38,930 So you could, in your input message, say something like how much tip would you like to give 10, 111 00:08:38,930 --> 00:08:39,770 12, 15? 112 00:08:40,070 --> 00:08:42,200 Please don't add any percentage signs. 113 00:08:42,380 --> 00:08:44,200 Just add the number or something like that. 114 00:08:44,810 --> 00:08:51,590 But again, once we've done this, it's not stored anywhere unless we add it into a variable. 115 00:08:52,100 --> 00:08:59,660 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 116 00:08:59,660 --> 00:09:02,150 a whole number, 10, 12 or 15, 117 00:09:02,150 --> 00:09:02,470 right? 118 00:09:02,870 --> 00:09:08,960 So depending on what you think is best, you can either turn this into a float or in my case, I'm probably 119 00:09:08,960 --> 00:09:11,790 going to convert it into an integer. 120 00:09:12,560 --> 00:09:17,290 So now we're onto the final step, which is how many people to split the bill between. 121 00:09:17,750 --> 00:09:21,050 So let's go ahead and create a variable called people. 122 00:09:21,560 --> 00:09:29,690 And I'm going to add an int wrapper around this input so that even in the very beginning, we know that 123 00:09:29,690 --> 00:09:35,600 we have to convert the number of people into a whole number because I've never had a meal with 124 00:09:35,600 --> 00:09:36,930 3.5 before. 125 00:09:37,850 --> 00:09:41,870 So the input is going to be how many people to split the bill. 126 00:09:43,400 --> 00:09:49,850 And at this point, they should enter the number of people which will turn into an integer stored inside 127 00:09:49,880 --> 00:09:56,180 this variable called people. So now that we've got all the data collected from the user, we're finally 128 00:09:56,180 --> 00:09:57,500 ready to do some math. 129 00:09:58,040 --> 00:10:08,210 And we said that the way to work out the tip is by multiplying it by 1. and then the number after 130 00:10:08,210 --> 00:10:12,180 the decimal point is whatever percentage they decided to give. 131 00:10:12,560 --> 00:10:18,510 So it would be 1.1 if it was 10 percent and 1.15 if it was 15 percent. 132 00:10:19,130 --> 00:10:23,630 Let's go ahead and calculate the bill_with_tip. 133 00:10:24,990 --> 00:10:32,370 So remember how we said that before the tip percentage is equal to the whole number, 10, 12 or 15, 134 00:10:32,760 --> 00:10:38,190 divided by 100, which turns it into 0.1, 0.12 or 0.15, 135 00:10:38,730 --> 00:10:46,290 and then once this calculation is done, we can multiply it by the bill. And then finally we add that 136 00:10:46,290 --> 00:10:47,880 to the original bill. 137 00:10:49,050 --> 00:10:54,510 So let's go ahead and print this and just check to see that it looks sensible. 138 00:10:55,080 --> 00:10:58,080 So bill_with_tip is what we're going to print. 139 00:10:58,570 --> 00:11:01,160 And let's put some easy numbers in there. 140 00:11:01,680 --> 00:11:06,820 And let's say that the bill was a hundred dollars and the tip was 10 percent. 141 00:11:07,350 --> 00:11:10,830 So then the 10% of hundred dollars is ten dollars. 142 00:11:11,070 --> 00:11:12,540 So the bill_with_tip, 143 00:11:12,810 --> 00:11:18,540 that's what's going to be printed next, should be 110. So we can type anything in here because 144 00:11:18,540 --> 00:11:19,380 we're not using it. 145 00:11:19,680 --> 00:11:24,550 And you can see that this calculation, bill_with_tip, is 110, which is what we want. 146 00:11:25,170 --> 00:11:28,350 Now, there's a lot of other ways that you can express this. 147 00:11:28,850 --> 00:11:36,690 For example, you could say, bill * (1 + tip/100). 148 00:11:37,320 --> 00:11:40,630 So this would actually give you the same result as well. 149 00:11:41,250 --> 00:11:47,010 But remember what we said previously about how Python is a little bit weird with floating-point numbers. 150 00:11:47,550 --> 00:11:51,570 But essentially this is still giving us the same result, which is 110. 151 00:11:52,500 --> 00:11:55,940 So you can choose whichever way you find most intuitive. 152 00:11:55,950 --> 00:12:00,340 And if you want, you can even split this up into several steps, right? 153 00:12:00,360 --> 00:12:05,580 We could say that tip_as_percent is equal to tip/100. 154 00:12:07,080 --> 00:12:16,530 And then we can multiply the bill by the tip_as_percent to get the total tip amount. 155 00:12:18,990 --> 00:12:26,290 And then finally, we can get the total bill by adding the bill to the total_tip_amount. 156 00:12:27,270 --> 00:12:32,430 Feel free to do this whichever way makes sense to you, but I'm going to leave it with as many steps 157 00:12:32,430 --> 00:12:37,320 as possible so that you can actually work through the logic if you got stuck on this math. 158 00:12:38,760 --> 00:12:44,070 Now, the next thing we need to do is to divide the total bill by the number of people. 159 00:12:44,370 --> 00:12:47,430 So if we had five people, then we would divide it five ways, 160 00:12:47,430 --> 00:12:47,710 right? 161 00:12:48,210 --> 00:12:51,750 So let's call this bill_per_ 162 00:12:53,050 --> 00:12:59,560 person, which is going to be equal to the total bill divided by the number of people. 163 00:13:01,280 --> 00:13:08,000 Now, at this stage, this bill_per_person is a floating-point number, so it could have many, many 164 00:13:08,000 --> 00:13:10,000 digits after the decimal point. 165 00:13:10,490 --> 00:13:16,910 If we want to round this to two decimal places, then you might remember from some of the lessons today, 166 00:13:17,240 --> 00:13:19,790 we have access to a function called round. 167 00:13:20,300 --> 00:13:26,090 And here we can add the number that we want around, which is the bill_per_person, 168 00:13:26,570 --> 00:13:33,530 and then after a comma, we can specify how precise, how many numbers or how many decimal places do 169 00:13:33,530 --> 00:13:35,030 we want to round this bill to. 170 00:13:35,510 --> 00:13:38,120 And in our case, it's two decimal places. 171 00:13:38,780 --> 00:13:47,570 So now this is the final amounts, which I'll call final_amount which is the bill_per_person rounded 172 00:13:47,570 --> 00:13:49,190 to two decimal places. 173 00:13:49,790 --> 00:13:57,190 And we can now finally print this to the user and say each person should pay... 174 00:13:57,830 --> 00:14:03,740 And remember, you can either use string concatenation which will require you to convert this number 175 00:14:03,740 --> 00:14:09,380 into a string again, or use the trick that we learned in the previous lessons where we can create an 176 00:14:09,380 --> 00:14:17,300 fstring by adding F in front of the string and then using some curly braces to insert the final amount 177 00:14:17,300 --> 00:14:17,930 right here. 178 00:14:18,620 --> 00:14:27,820 And we can write the final_amount dollars or we can put a dollar sign in front and maybe a colon here. 179 00:14:28,460 --> 00:14:34,160 And now if we clear our console and run our code, then you'll see it work. 180 00:14:34,190 --> 00:14:35,770 So welcome to the tip calculator. 181 00:14:35,780 --> 00:14:36,910 What was the total bill? 182 00:14:37,220 --> 00:14:38,990 Let's make up some random number. 183 00:14:39,560 --> 00:14:40,910 What percentage tip? 184 00:14:40,910 --> 00:14:47,780 Let's say we're going to get 15 and then we're splitting it between five people. And it calculates everything, 185 00:14:47,780 --> 00:14:49,370 doing all of that maths. 186 00:14:49,730 --> 00:14:55,940 And finally, it rounds it to two decimal places, giving us the final amount each person should pay. 187 00:14:56,780 --> 00:14:59,440 But what if we test it out with the initial numbers? 188 00:15:00,200 --> 00:15:07,700 Let's hit, run and let's try to put in 150 dollars as the total bill, and then we're going to give 189 00:15:07,700 --> 00:15:11,180 a 12 percent tip and we're going to split it between five people. 190 00:15:11,750 --> 00:15:16,520 Notice that is telling us that each person should pay $33.6. 191 00:15:16,880 --> 00:15:20,960 But normally, we're used to seeing that rounded to two decimal places. 192 00:15:21,440 --> 00:15:23,960 But we have that round function here already. 193 00:15:24,230 --> 00:15:26,060 So why is it not doing its job? 194 00:15:27,160 --> 00:15:32,830 Well, if you think about it, the result of this calculation is just 33.6. There's 195 00:15:32,830 --> 00:15:40,390 nothing after the six, but we want it to display a zero. And this is a formating problem rather than 196 00:15:40,390 --> 00:15:42,200 a mathematical rounding problem. 197 00:15:42,670 --> 00:15:43,810 So what do we do? 198 00:15:43,840 --> 00:15:50,410 Well, we go to our good friend Google whenever we're stuck and we're going to search for how to round 199 00:15:50,410 --> 00:15:55,890 number to two decimal places in Python. 200 00:15:56,620 --> 00:16:02,260 And if we take a look at the first Stack Overflow question, you can see that this person had pretty much 201 00:16:02,260 --> 00:16:04,240 the same problem that we had. 202 00:16:04,630 --> 00:16:11,980 And if we're scrolling down, you can see that the solution is to use some sort of formatting. And we 203 00:16:11,980 --> 00:16:17,260 can try out each of these examples one by one in code to see how they work, 204 00:16:17,500 --> 00:16:21,490 and we can also take a look at the documentation that they link to. 205 00:16:22,360 --> 00:16:29,890 So the actual way that we do this is by using a colon and then dot and then we specify that after the 206 00:16:29,950 --> 00:16:36,120 dot, we want two decimal points in our float. And we use the format function to do this. 207 00:16:36,460 --> 00:16:43,360 So instead of using round, we can create this final amount variable by creating a string using that 208 00:16:43,360 --> 00:16:52,630 format, :.2f, and then we can use the format function to pass in that bill_per_person. 209 00:16:54,230 --> 00:17:03,740 And now when we run this again, using the same inputs, we now get a .60 at the very end 210 00:17:04,220 --> 00:17:10,190 and this is basically turned this bill_per_person, which is a float into a string. 211 00:17:10,400 --> 00:17:16,680 And that string is abiding by this particular format, which is the two decimal places. 212 00:17:17,330 --> 00:17:19,370 How did you get on with this project? 213 00:17:19,610 --> 00:17:25,550 Did you manage to get it in one go without having to look at the solution? If you got stuck at any point 214 00:17:25,550 --> 00:17:27,950 or if your code didn't work as you expect it to, 215 00:17:28,280 --> 00:17:33,110 this is a time to go back to it, fix it, and make sure that you've understood everything that's been 216 00:17:33,110 --> 00:17:35,150 covered through this exercise. 217 00:17:35,480 --> 00:17:40,310 But if you already created it and it's working perfectly, then you're ready to go out there with your 218 00:17:40,310 --> 00:17:41,600 tip calculator in hand. 219 00:17:41,960 --> 00:17:47,430 Remember that you can save the URL of your tip calculator in your phone as a bookmark. 220 00:17:47,450 --> 00:17:52,040 So the next time you go out and have dinner or lunch with friends, then you can crack open your own 221 00:17:52,040 --> 00:17:54,800 tip calculator and figure out the final bill. 222 00:17:55,670 --> 00:18:01,130 So I hope you had fun building this project and doing all of the coding exercises and learning about mathematical 223 00:18:01,130 --> 00:18:09,350 operations, fstrings, data types, type conversion, and all of the things that we did today. Have a rest 224 00:18:09,350 --> 00:18:15,500 and I'll be back tomorrow teaching you about conditional statements and how we can get the program to 225 00:18:15,500 --> 00:18:21,500 do different things depending on certain conditions or certain parts of our code. 226 00:18:22,100 --> 00:18:25,360 So I bid you good night and I'll see you tomorrow. 24816