All language subtitles for 11. Day 2 Project Tip Calculator

Hey guys,
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Welcome to the final project of today and in this final project we're going to
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be building a tip calculator.
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So the final output is going to look like this. 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
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$124.56 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% tip, so we entered 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 is a seven of us and then hit enter. Finally,
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it's going to tell us that each person should pay about $19.93. Notice how the
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final bill, even though after all of these calculations,
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it's probably got more numbers after the decimal point,
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we only want two decimal places of accuracy,
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so it should be rounded to two decimal places.
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The second thing to remember is that these are percentages and in order to
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calculate a percentage of something,
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you can multiply a number by the percentage number divided by a hundred. Let me
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show you this in a little bit more detail.
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If you head over to repl.it/@appbrewery/tip-calculator-
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start,
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then you've got these starting file for this project. And here I just want to
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quickly show you how the math works because this project is not about testing
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your maths.
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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. If we were to apply a 12% tip on top of
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that,
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then 12% is going to be equal to 12 / 100 which is equal to
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0.12. Now the next step is we can multiply 150, the total bill, by 0.12 and this
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will give us what 12% of 150 is
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which is 18. Now we of course have to add the tip onto the final bill,
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so it becomes 150 + 18. So $150 with 12% tip is equal to $168. Now a
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shorthand way of doing all of this is simply multiplying 150 by 1.12. So the one
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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,
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you come across some sort of number that looks a little bit strange because you
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think 150 multiplied by 1.12 should actually equal 168 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,
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then I'll link to this page in the Python documentation where they tell you why
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this is happening. But be warned, it's pretty dense and it's pretty heavy.
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But the final conclusion is it's just a way that Python is approximating this
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number. 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 the split it between five people.
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So 168 divided by five is equal to 33.6. Now what we want to show the user is we
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want to show them the amount that they have to pay with two decimal places of
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accuracy.
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So we want to say something like 33.60 if this is the case because that's
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normally 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
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decimal places. If you have successfully created this program,
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then it should work exactly as this example version would,
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which you can find if you go to tip-calculator
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-end.appbrewery.repl.run and you'll be to see the formatting where it
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actually tells you each person should pay this particular dollar amount and it's
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rounded to two decimal places.
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And this is the amount after taking into consideration these three different
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inputs from the user.
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Have a play around with the final product and then have a think about how you
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would create this program step-by-step and then give it a go by forking this
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starting repository to your own account and then try to achieve this result.
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This is going to test everything that you've done so far, including f strings,
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including complex mathematical operations,
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including PEMDAS and calculating numbers
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and the order in which mathematical operations are run by a computer as well as
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everything you've learned in the previous lesson in previous days as well.
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I think this is going to be a lot of fun and the end result is going to be kind
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of useful the next time that you need to split the bill between friends.
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So I'm going to let you pause a video and get on with it.
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And then once you're done,
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if you want to, head back over here and I'll walk through the solution with you.
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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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[inaudible]
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Okay,
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so we've seen how the program is supposed to work and we're trying to create it
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from scratch by reverse engineering it essentially.
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The first thing I'm going to do is I'm going to fork the starting project and
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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. We just have to create a print statement. Perfect.
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And if you're creating a really enthusiastic tip calculator,
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you can replace the full stop with an exclamation Mark. Okay,
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so let's run it step by step to make sure that we don't have any errors along
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the way. So the first step seems to be working.
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Now the next step is to ask the user for some inputs and we want to know what
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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
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work with because when we actually run this,
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you'll see that the input will go straight after the end of that string,
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so at the dollar sign. So now we can enter a dollar amount like this,
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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
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into this input.
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Now remember that this bill is going to have a data type of a string,
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right?
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So if I go ahead and hit run and let's just type some numbers in here,
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you'll see that the data type of the bill is, as we said,
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a string. In order to be able to do maths,
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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. Now in this case,
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because the bill is likely to have numbers after the decimal place,
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it's probably better that we turn it into a float so that we get the most
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accurate result possible. Now that we're done with the bill,
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the next question the tip calculator should ask is what percentage tip would
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you like to give 10, 12, or 15, or you can, of course, switch this up depending on
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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,
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I'm asking the user how much tip would you like to give and giving them some
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examples and notice how in my examples,
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I don't actually have the percentage sign here because I don't really want them
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to type the percent sign into this input.
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Because if they do,
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when they say 12%, this is going to be really hard for me to turn the 12% into an
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actual number. So you could, in your input message,
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say something like, how much tip would you like to give?
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10, 12, 15? Please don't add any percentage signs,
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just add the number or something like that. But again, once we've done this,
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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,
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which is going to be a whole number 10, 12, or 15 right?
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So depending on what you think is best,
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you can either turn this into a float or in my case I'm probably going to
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convert it into an integer.
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So now we're onto the final step,
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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
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beginning,
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we know that we have to convert the number of people into a whole number because
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I've never had a meal with 3.5 people 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
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integer stored inside this variable called people.
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So now that we've got all the data collected from the user,
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we're finally ready to do some maths.
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And we said that the way to work out the tip is by multiplying it by 1.
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and then the number after the decimal point is whatever percentage they decided
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to give.
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So it would be 1.1 if it was 10% and 1.15 if it was 15%. Let's go ahead and
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calculate the bill_with_tip.
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So remember how we said that before the tip percentage is equal to the whole
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number,
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10, 12, or 15, divided by a hundred which turns it into not 0.1 or 0.12 or 0.15.
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And then once this calculation is done,
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we can multiply it by the bill. And then finally we add that to the original
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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 and let's put some easy numbers in
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there.
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Let's say that the bill was $100 and the tip was 10% so then the
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10% of a hundred dollars $10 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
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here because 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
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want. Now, there's a lot of other ways that you can express this.
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For example,
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you could say bill * (1 + tip /100). So this would
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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
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floating point numbers, but essentially this is still giving us the same result,
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which is 110. So you can 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
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_amount.
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And then finally we can get the total_bill by adding the bill to the total_tip
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_amount. Feel free to do this whichever way make sense to you,
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but I'm going to leave it with as many steps as possible so that you can
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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
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people. So if we had five people, then we would divide it five ways, right?
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So let's call this um,
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bill_per_person,
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which is going to be equal to the total_bill divided by the number of people.
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Now at this stage,
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this bill_per_person is a floating point number,
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so it could have many, many digits after the decimal point.
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If we want to round this to two decimal places,
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then you might remember from some of the lessons today we have access to a
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function called round.
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And here we can add the number that we want to round which is the bill_per_person
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and then after a comma, we can specify how precise,
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how many numbers or how many decimal places do 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 amount
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which I'll call final_amount,
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which is the bill per person rounded 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,
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which will require you to convert this number into a string
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again or use the trick that we learned in the previous lessons where we can
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create an F string by adding F in front of the string and then using some curly
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braces to insert the final amount right here. And we can write the final_amount
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dollars or we can put a dollar sign in front and maybe a colon here and now if
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we clear our console and run our code,
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then you'll see it work. So welcome to the tip calculator.
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What was the total bill? 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.
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And it calculates everything doing all of that maths.
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And finally it rounds it to two decimal places,
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giving us the final amount each person should pay.
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How did it 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?
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If you got stuck at any point 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,
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and make sure that you've understood everything that's been covered through this
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exercise. But if you've already created it and it's working perfectly,
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then you're ready to go out there with your tip calculator in hand.
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Remember that you can save the URL of your tip calculator in your phone as a
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bookmark. So the next time you go out and have dinner or lunch with friends,
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then you can crack open your own tip calculator and figure out the final bill.
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So hope you had fun building this project and doing all of the coding exercises
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and learning about mathematical operations, F strings, data types,
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type conversion,
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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
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can get the program to do different things depending on certain conditions or
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certain parts of our code.
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So I bid you good night and I'll see you tomorrow.