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Alright so we're all set up now so

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it's time to start learning Kotlin,

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so start Android studio and then open the

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Kotlin tutorial project so I'm gonna

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open up this by clicking on Kotlin

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tutorial and just a reminder to ignore

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the outdated Kotlin runtime or messages

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of that nature for this particular

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project because we've had to hack things

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together to get it to work, so if you

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do that you'll find that things won't

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work properly. Alright now open up the

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main dot kt file by double clicking it

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if it's not already showing on the

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right-hand side of the screen, in my case

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it was already open and by the way if

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you want to close it at any time you can

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come over here and click on the X to

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close it and then we'll click it to open

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it again so that's what you do when you

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want to work with different files you

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can just choose which ones to appear in

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the tab list above the editor window

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here and you can have multiple ones on

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that list and click on to select the

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different ones now unlike Java you don't

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need to create a class to hold your

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Kotlin code and if I keep referring to

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Java in this tutorial things are going

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to get very confusing for students who

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don't understand Java.

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Now there's one example I've just talked

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about classes and we haven't even

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discussed what they are yet so for most

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of this tutorial section I'm not going

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to keep comparing things to Java I won't

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promise not to mention Java now and then

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but I won't do it very often we will

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start by looking at that simple function

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on-screen here that just prints out

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hello world that you saw running in the

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previous video. Now that looks a bit

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horrible but this particular function

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has to follow that format now the reason

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is that the computer needs to know which

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function it should start with when you

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run your program so you have to start

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with a function called main that has a

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declaration exactly like we've got here

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on line one now things are a bit

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different when creating an Android app

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rather than a Kotlin program but at the

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moment we're learning Kotlin so we have

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to use a main function in this form now

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the keyword fund defines a function and

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our functions called main you everything

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between the opening and closing braces

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as these here at the end of line 1 and

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the style of line 3 that's part of this

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function now inside the function is the

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code that's executed when our program runs

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make sure you put your coat in between

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these two curly braces so you can see

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here on line one on line three when you

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want it to be executed as part of this

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function so this function prints out the

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message helloworld which is what this

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print line statement here on line two

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actually does. Now Kotlin programs are

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normally a lot more complex than this

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they contain a lot more classes and

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functions and can also repeat bits of

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code and so forth but this is a very

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basic Kotlin program so what our

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function is doing is calling another

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function called print 'ln and that's

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short for print and start a new line and

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the functions part of the Kotlin library

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so that just means it comes with Collin

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to give us a way to print things so we

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tell it what to print by putting what's

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called an argument inside these

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parentheses as you can see here on line

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two so that's the argument that's in

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between those two in between the

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parentheses or inside the parentheses

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and here the argument is the text hello

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world in double quotes and by the way

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because we're dealing with text rather

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than numbers we enclose hello world in

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speech marks all these double quotes as

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we call them in Australia so our main

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function uses another function called

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print 'ln to print the text that we've

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given it. Now arguments are values that

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you provide to functions to give them

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the information that you want them to

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work with so the print line function

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needs to know what to print and we tell

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it by giving it a string of characters

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enclosed in these speech marks or double

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quotes so let's just run the program

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again to see if it's doing what we

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expect so what we can do we can also

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right-click in here within the editor

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window to get the context menu right

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click it and I'm going to select main

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Katie if I select that you can see down

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the bottom bottom left-hand corner we've

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got holo world showing on the screen now

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the console should have opened up

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automatically but if it doesn't you may

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need to click on this run tab at the

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bottom of the screen over here and say

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you've got to turn it off and turn it on again

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so if it's open it's it'll close when I

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click it if it's closed

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I'll open it'll open when I actually

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click it again alright so there's our

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holo world text printed out now when a

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program runs without any errors

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we'll see that the message at the end

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says price has finished with exit code

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zero. Now normally an extra code other

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than zero means that something's gone

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wrong but you'll normally get an error

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message as well so you'll know if that

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hasn't worked.

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So let's actually print something else

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out so they'll come down here and type

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in print 'ln they're going to type my

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first Kotlin program and we've got this

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red squiggle at the end of the line as

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you can see over here and over to the

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right-hand margin is a red dash over

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here. Now Edward studio does that to

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indicate errors and warnings we'll be

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seeing some warnings later they'll

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appear in a different color

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normally orange or amber and you can

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choose to ignore those it's a good idea

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that one to at least read them though

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because they'll often highlight problems

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with your code the warnings won't stop

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the code from running but they could

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mean that it won't do quite what you

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expected but these red arrows Oh can't

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be ignored the code just won't run when

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you've got errors like this so to see

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what the actual error is you can hover

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the mouse either over the school over

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here or over here in the right margin

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the arrow is just saying expecting and

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then in single quotes our right

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parenthesis so it's just telling us that

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the line must end with the closing

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parenthesis now computers are very picky

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and it's important that your code

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follows the syntax of the programming

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language exactly you'll pick up the

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rules by reading and writing code so

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don't think that you have to remember a

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whole lot of complicated grammar before

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you can program if you do make mistakes

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which you will because it's a natural

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part of learning to program then Android

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studio or the Kotlin compiler will give

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you errors to indicate what's wrong now

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there's nothing actually wrong with

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getting errors it's a natural part of

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learning how to program you know I wish

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I could claim that I never get errors in

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my code but even after over thirty years

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of programming I still make mistakes so

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don't worry the more mistakes you make

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though that probably means you're

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learning faster so unlike human

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languages computer languages are very precise

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you have to stick to the syntax of the

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language and if you think about it even

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human languages need correct punctuation

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though being intelligent we can often

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work out what so really meant if the

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punctuation isn't quite right but

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punctuation is still important have a

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look at this slide now here's exactly

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the same text but punctuated in two

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different ways and if you haven't read

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of both of those you'll see that there's

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a big difference just by adding

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punctuation in appropriate places so if

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you do find yourself getting frustrated

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remember that that it's only a computer

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he can't think for itself and you have

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to compensate for that by being very

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precise in how you write your code so

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that the poor computer can understand

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you. Alright so back to Android studio

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so it's telling us there's something

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wrong here,

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so I'm going to add the closing

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parenthesis to the end like so and

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notice that the red - the has

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disappeared as well as the red lines in

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the right side of the screen the right

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margin, so now that we haven't got any

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errors we can run this again and now

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that I've already run the program for

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the first time by right clicking I can

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just actually come up here to the green

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triangle up in the toolbar I can click

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on that now that doesn't always work

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until you be the right clicked and

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chosen the function you want to run or

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use the run menu now you can see on

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there there's already been different

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options for running so I'm click on that

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you've got different options there but

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we've only got the one file here they've

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only got may end up Katie so if you end

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up running the wrong program later in

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the course either right-click on the

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code well it's in the editor that you

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want to run or use the menus to come up

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here and then choose the actual menu but

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in our case we've just got the one menu

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of the one file because that's all we've

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worked on up until this point in the

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course so after that the green button

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should work for whatever map function

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you're trying to run but you will have

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to tell it to run it the first time,

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so if I just click on that now you can see

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we've got hello world there my first

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Kotlin program. So then you've got a

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function containing two lines to execute

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and unless we do something to tell it

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otherwise, Kotlin will just start at the

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top and obey the instructions on each

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line until it gets to the end,

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we can't have a look at what we can do

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to make it behave differently shortly

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but before that we need to have a look

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at variables or properties we'll do that

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in the next video.