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Welcome back in this video, we are going to look at functions and functions are something that we have

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used already.

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For example, the main function and now we're going to see how we can create our own functions, which

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we then can use to reuse code very easily.

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And in order to do so, I'm going to clean up this whole main function now because it's going to be

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a lot clearer if we have everything on one screen.

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So we have this main function.

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And as you know, this is the entry point of our program and that's where everything begins.

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So if no code isn't here, then nothing will happen if we start to program.

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So that's important to know.

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And you know that already.

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So the next thing we can do is we can create code outside of this function and then call it within this

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function.

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And in order to do so, you can just go ahead and create a new function with the keyboard fun.

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And then you give this a name, and I'm just going to call this one my function.

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And this is generally the structure that you have, so you have this keyword fund.

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Then you have a name for the function.

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You have round that brackets and then you have curly brackets.

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And within the rounded brackets, you can put all your parameters within the curly brackets.

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You can add to code block that should be executed once this function is called.

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So what do all of these terms mean and what we will see in the second?

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So let's get started first with something very basic.

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So I'm just going to use print here, and I'm just going to say called from my function.

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All right.

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So now let's just call this my function.

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How do we call a function?

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Well, we call it by just using the name of the function and then the brackets here.

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And if we have any arguments that we want to pass, then we need to pass them as well.

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So let's run this code just to see if this is working.

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And once you run it, you will see that it's going to say call from my function.

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All right.

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So this print statement that was within my function, so within the function that we called my function

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was called once we called this function here.

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So if we decide to call this function twice, then it's going to display called for my function twice

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here and that we are called for my function and again called for my function.

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And as we are using a print statement, they are told directly after another.

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So there is no space in between or a no line break either.

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So this is our very basic function called my function.

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Now we can extend two functions and in order to do so, I'm going to create a new function so we can

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make functions a lot more complex.

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For example, I can call one add up, and I'm just going to have two variables here.

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I'm going to have one variable, which is of Typekit and another variable, which is also of Typekit,

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and it should return a variable of type.

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So what do all of these things do?

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Well, first of all, we have two parameters here.

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So there's this parameter one, which is called a which is of type integer.

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And then we have another parameter, which is called B, and it's also a type integer.

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So now the key word here is parameter.

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All right.

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So we have two parameters here.

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Then after the colon, we say of which type the return type should be.

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So in this case, our function add up is going to return something once we call it.

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So instead of just executing some code in there, it's also going to return something.

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So it's going to give us something back that we can then reuse.

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OK, so the idea here is that we need to use the return keyword.

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As you can see, it's complaining here.

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So now it's complaining about the returns.

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So let's say I always return zero.

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Then this add up would always return zero, no matter what I put into it.

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So let's change that a little bit.

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Let's say I want to actually add up those two values.

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So A and B.

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So what we will do is we would return a plus B in this case because we want to return whatever A and

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B are added up.

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Now it's going to return whatever is the result of A-plus B.

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So our parameters is the definition of the input that we want to have and then we have an output.

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And it's also of type int.

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So whatever will return will be our output and it should be of the type that we have defined here.

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Parameter input and then return type is our output.

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OK, so now we can go ahead and use this function, add up in our main function, so I'm going to get

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rid of my function calls here, and I'm just going to call add up and I'm going to add up with five

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and three.

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So this should return eight.

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Now the thing is, it will return eight, but we have no way of knowing that it returns eight, except

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for, let's say, we stored in a variable or we use our debugging tools.

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But I'm just going to store it than a variable, which I'm going to call result.

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And it's going to be the result of whatever add up is going to come up with and it's going to store

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it in result.

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So now what I'm going to do is I'm just going to use result is and concatenation year result.

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So very basic.

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And of course, we're getting.

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The template requests here, so this is the alternative way.

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All right, so the result is results.

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And now we can go ahead and test what we're actually going to get.

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So there we are.

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It says results as late as you can see, it worked.

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So the input was five and three and the output was eight.

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And that is what we saw as a result.

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Now there is something to say about the terms here because here.

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What we are using is called parameters, right, and so we are using parameter and parameter beat now

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when we pass a value to our function called add up, this is an argument and this is also an argument.

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So the term here is argument.

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All right.

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You're not having an argument here, but we are using arguments.

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OK, so the idea is that they are two different terms and this is something that people mix up all the

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time.

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And yeah, in some cases, they really just ignore the whole concept of parameter, an argument or distinguishing

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between the two.

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So either parameter or argument is going to be fine when you use it in combination with functions.

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OK, but be aware that there is a difference between the term argument and parameter.

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So I might even mix them the term term sometimes when talking about function, so please be forgiving.

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Then there is another thing about functions and you probably heard the term or maybe heard the term

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methods.

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So there is this called method, and a method is a function within a class.

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So that's the only difference between the two.

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Otherwise, they are the same.

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So in some programming languages which are not object oriented programming languages, then it's always

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going to be a function.

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But in programming languages which are object oriented, it's going to be most of the case as a method

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because it is defined within a class.

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In our case here, however, we're not having a class.

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So it's not like in our main activity.

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For example, in our class main activity there, we have a function called on create.

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But to be more precise, this is a method because it is within a class.

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So it is a method here.

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There are a bunch of other words that come up in programming languages, right?

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And what it really helps is a dictionary sometimes.

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So Kotlin programmer dictionary, you can find it under blog Scotland Monice Academy dot com.

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So they wrote a little dictionary with the main words here.

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So function versus procedure, then function versus method and so forth.

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So here are a bunch more field versus property.

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What's the difference here?

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Parameter versus argument?

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That's something that we have seen before and so forth.

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So if you want to really dig deep into all of the different terms and terminology, then check out this

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article here.

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All right.

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So coming back to our cut on basics, a little challenge for you, please write another function which

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will not add up, but which will build the average of two values.

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So here you have to be careful with the data type.

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And yeah, just please try to build that function by yourself.

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All right.

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So let's go ahead.

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I hope you tried it.

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So here I'm just going to use the funky word and then I'm going to call this one a veggie setting for

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average.

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And I need two values.

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One of them will be a double and the other one should also be a double.

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So the thing about those is that the return of an average usually is not a whole number.

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So that's why I'm using doubles here, and it's going to be a double as a return type as well here.

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And then we can return a plus b divided by two.

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That's going to be it.

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So now, of course, we can see what the result is, so let's call this one average instead.

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And we're going to not call the add up function, but we're going to call the average function.

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And I'm just going to say, OK, what's the average of five and 13 and then?

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In order to be precise, we need to make those double so five point three and thirteen point thirty

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seven.

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And no less around us and that we are to as result is nine point thirty three, four or five.

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All right.

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So these are the basics of functions, so what's the whole point of functions?

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Well, there are multiple advantages of functions.

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So one of them is that you can reuse code.

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Another one is, for example, that you can work with a partner so you take care of one piece of code

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and he takes care of another piece of code or she takes care of it.

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And then you can just combine them by having functions that you can then reuse.

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So you can write your own functions and then you can both use the functions of the other person.

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And then another thing is that you can use functions that are prebuilt and you can just use the functionality

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of them.

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So that's the whole idea of functions.

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They add functionality to your program and you can simply use them for whatever purpose you built them

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or for whatever purpose they were built.

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And there are gazillions of functions out there that you can reuse just by using this import feature

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here.

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As you can see here, import Android OS bundle well in there, there are a bunch of functions that we

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can reuse.

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So if you open up the bundled class, for example, you can see that in there you have.

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A bunch of.

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Constructors, but then we have a maybe pre-filled has f the s function, then we have another function

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called.

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For Pear, which is going to return a bundle.

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Well, you might wonder what all of these public aesthetic bundle keywords mean.

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Well, the thing is this is Java coat.

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So this is not codling coat.

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And in Java, the structure of a function is slightly different than it is in codling.

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All right.

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But the basic idea is the same.

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It's has a return type, then it has a name, and then it has a bunch of parameters here.

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Just the order is a little different.

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But in the end, what it does, it has a bunch of code that you can then reuse.

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So no worries if you don't understand the stuff that is going on in here.

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Because for one, it's not Kotlin code.

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And the second thing is you don't need to understand everything behind the function in order to use

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the function.

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Sometimes you just need to have the output right, and that is really powerful.

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It's like driving a car.

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You don't have to be a mechanic in order to drive a car, or you don't need to be able to repair a car

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in order to drive a car.

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You can just sit in there and be happy about all of the features that were added to the car and that

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you can now use.

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All right, so these are the basics of functions.

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And yeah, let's check out the next video where we're going to look at knuckleballs.

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So see you there.