All language subtitles for 8. [Dart] Functions Challenge

All right.
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So now that you've learned about all three types of functions, it's time to challenge yourself with an
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exercise.
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And in this case, I've created a pre-built dartpad for you with some code that I've already written.
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And you can access this exact same dartpad by heading over to this URL which I will of course linked
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to in the course resources for this lesson.
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Now once you get here, you can see that we have a challenge for you.
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And the idea is that without changing this main function so without touching any of these lines of code
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that are already written,
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I want you to make this code work and get the result printed in the console. In order to achieve this,
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you're going to need to create a add function and also a multiply function, because at the moment, this
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is what our Dart analysis is telling us that doesn't exist.
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So there's no add function and there's no multiply function.
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So somewhere down here after the main function, create these two functions, add and multiply.
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Making sure that you spell them exactly the same and also match up the input parameter names where there
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are any.
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Once you've completed the challenge, firstly all the errors should go away and it should now look like
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this.
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And when you click run, it should print the result which in this case should be 23.3
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recurring into the console. The way that we're able to calculate this is because our add function adds
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our two numbers, where we give it as inputs 5 and 9 together.
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So 5 + 9 = 14.
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And then that 14 becomes the result of this right hand side,
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and it goes into the next step where we tried to multiply 14 by 5.
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So there's multiply function has to multiply this value by this second value.
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I've obviously hidden what the steps are in order to achieve this
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so that you can test yourself and see if you can make this work.
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So pause the video now and try to complete this challenge.
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All right.
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So how did you get on?
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Well in order to complete this challenge, you need to have a good grasp of functions.
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So the first thing we'll address here is that right here, we are creating a new variable that has a data
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type of int,
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so a whole number. And it's going to be storing something that comes out as the output of this function.
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The function has to be called add, and it takes two inputs, n1 and n2,
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and in this case we're saying 5 and 9. And inside this function obviously we need to add 5 to 9
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in order for it to come out as our result.
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So let's create our function now.
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Previously we've always started with void.
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In this case because we want to have an output,
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and in this case we want to output a whole number,
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we're going to start with the keyword int. And then we're going to provide the name of our function, which
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is called add.
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And you can see that once I put in that word, then my error for the add function goes away. This is the
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bare bones of my function so far. But I now need to say that it provides some inputs.
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And in this case because we're able to call add and provide our inputs with named parameters or named
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arguments, we have to add in those curly braces in here so that we can write int n1 and int n2.
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So what this does is it says that when you call the function add, you can provide the name of each parameter,
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just like we have done here. And both inputs are going to be integers,
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so we have the int keyword in there.
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And then inside the function, we're simply going to add n1 to n2. So you can either create a variable
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called result and you write equals n1 + n2, and then you can output the result by using that
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return keyword.
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So you write return result. And this will get rid of all our errors to do with our step 1.
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Now if this makes more sense to you, then be sure to write it like this, but you can also cut this down
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by one line. By instead of having to create that variable,
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you can also just simply return n1 + n2. And we can remove this line entirely.
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So that does exactly the same thing but it combined that into one step. And we don't have to create that
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intermediate step that we had previously.
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Now that add is done, we have to create our multiply function.
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Let's go down here and create our multiply.
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It's also going to have an output of integer type because we can see that the variable that we're using
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to hold the data that comes out of this function, has the data type int.
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So this must have an output of int.
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So we're going to start off with int, and then we're going to give it a name.
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So it's called multiply, making sure those are spelled the same. But in this case, do you see that we don't
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have the argument names when we call the function?
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So we didn't have to write n1: or n2:.
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So that means we don't need those curly braces and we can simply just specify our data type and the name
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of our argument, which will again call n1 and n2. And they are also going to be integers.
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Now inside our multiply, we're going to of course return the result of multiplying n1 by n2. And
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this will come out of the multiply function as the output. And that output goes into here.
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So the output is gonna be equal to the step 2 result which then gets used in the next step of calculations
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where it gets divided by 3 and finally that final result is printed.
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So now when we hit run, we can see the final output is 23.3 recurring, and this is
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how you would solve this challenge.
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Now if any point of this challenge is confusing,
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be sure to revisit the lessons where we talked about functions in Dart part 1, part 2 and Part 3.
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But otherwise, we're going to get back to coding up our Xylophone app and trying to solve the problem
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that we had earlier on using our newfound knowledge.
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So all of that and more, I'll see you on the next lesson.