All language subtitles for 28. Challenge BMI Calculator Solution

All right. So we know that the formula is weight in kilograms divided by height squared, and we have to
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make this line of code work.
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So let's first try it out in the calculator.
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Let's say that we first try to square our height which is 1.8 meters.
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So on a calculator we can simply write 1.8 times 1.8.
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So 1.8 squared is equal to 3.24.
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So now we can divide 65 by 3.24. 65
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divide by 3.24 and we get 20.0617 something something something.
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All right. So now that we know that this is how we would calculate it on a calculator, then we can simply
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copy all of this starting code, and open up our Chrome Developer Tools, and paste it into our Snippets
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tool.
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So now, we're going to create our function below this line.
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And the first step to creating any sort of function is the function keyword,
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right? Then we're going to give our function a name, which we said has to be the name bmiCalculator,
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so we're going to use that name.
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Next step is some parentheses, and whether we're going to add some inputs in here.
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So in this case we're saying that put the input weight first and then put the input height.
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So our inputs are going to be weight and height.
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Now we get to open up our curly braces and specify everything that this function is going to do.
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So this function has to calculate the value of bmi.
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Remember that the formula is the weight divided by height squared.
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So bmi is going to equal to the weight input divided by the height input multiplied by itself.
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And remember, in the previous lesson we talked about Javascrpit numbers, that in order to specify the
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order of your calculations then you can use the parentheses to set precedence.
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So by putting those two parentheses there then we say that calculate height times height first and then
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divide weight by that value.
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So now in order to get value bmi out of this function, we have to use the return keyword, and we can say
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return bmi.
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So now, if we take all of this code and we go back to our exercise here, we paste it in here, and now if
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I hit Check solution, then you can see that it will pass.
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Now there's a number of different ways of writing this function.
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Some of you might have wondered,
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I don't really want to multiply the height by height in order to get it squared.
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Why can’t I just raise height to the power of 2?
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How would I do that in Javascript?
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Well, as with any query regarding programming, the solution is only a quick google away.
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So if we search for ‘raise a number to a power’ and we add the keyword Javascript, then you can see that the
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MDN docs come up with the Math.pow function, and it shows us how to use it.
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It says that we can simply say Math.
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pow,
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and the first number is the base and the second number is the exponent.
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So this is your squared which will be 2 or cubed which will be 3.
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And this is how you would use it.
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So let's try it out
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in our case. Instead of writing height times height,
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what if we did Math.
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pow, set of parentheses, and then we said height, 2, so height to the power of 2?
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Now, if we check our solution, you can see that our function is still working exactly as we expect it
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to,
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but it's now perhaps a little bit more elegant.
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Now, if you run this code as it is right now, for example we're calculating the BMI from 65 kilograms
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and 1.8, and then we're logging that BMI into the console,
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then you can see that we're getting a really long number,
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20.0672839 etc..
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Now usually with BMI we're working with whole numbers.
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So how can we turn this long number with loads of decimal places to simply a whole number?
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Well again Google is your friend.
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And if you search for ‘Javascript round a number to the nearest whole number’ or something around there, then
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the first result that you get is from W3 Schools, and it tells you about the round method, which you can
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use by saying Math.round, and is similar to the floor method, which simply rounded down your decimal
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place.
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But Math.round is more mathematically correct.
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So if it's 2.5 it will round it to 3, and if it's 2.4
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it’ll round it to 2.
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So let's try using this in our solution.
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So if, instead of returning bmi, we returned Math.round, and inside the parentheses we enclosed our
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bmi, as a number with decimal places.
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Now if we run our code you can see that we only get 20 back which is exactly what we wanted.
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And if you change our solution to this updated one inside our testing suite, then you can see that our solution
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also passes.
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So I hope that was interesting and we've got a few more of these challenges coming up for you.
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So keep your eyes peeled.
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But in the next lesson, we're going to dive deeper into Javascript, and we're going to learn all about
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control flow.
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So you have all of that and more to look forward to.
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So I'll see you on the next module.