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- Okay, so in this section
we're going to see how to build

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and run our first Rust application.

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Here's the code we're going to compile.

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It's hello world.rs simple main function.

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It calls the print ln macro,

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prints hello world on the console.

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What could be easier than that?

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Just a reminder, if you want
to do these demos for yourself

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you can go to the Rust dev demo folder.

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Lesson 01 getting started.

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That's the folder for the
demos for this first lesson.

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So let's just confirm that.

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So here we are.

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I'm in the Rust dev lesson
01 getting started folder.

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Here's the simple
application, hello world.rs.

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Later on in this lesson
we're also going to see

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how to create, build and run
an application using Cargo.

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We'll see that later

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but we'll just focus on
the simple example for now.

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Let me just open that
up in the code editor.

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So here we are.

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I'm using Visual Studio Code.

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As I was saying previously,
other editors are available.

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Sublime, Eclipse, VIM,
anything you fancy really.

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If you are going to use Visual Studio Code

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there are extensions available too

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so that you can actually
run the application directly

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within the Visual Studio Code environment.

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And I was tempted to illustrate
that in the video series

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but I decided not to

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because you might be
using a different tool

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and I didn't want to kind of mandate

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or make you feel like you had
to use Visual Studio Code.

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But if you are interested, have a look

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at the extensions and
download the extensions

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for Rust and it'll definitely
help your experience.

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What I'm going to do is
I'm just gonna compile

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the application from a
normal command window.

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So let's see how to do this.

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Just open a command window,

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go to the folder where your code is

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and then run the Rust compiler rustc.

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Give it the name of your application.

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Quite straightforward, really.

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What it'll generate

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obviously the executable, your
application that you can run.

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If you're on Windows, it
also generates a PDB file.

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This is a like a programming
debug information

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so that it helps you single
step through the application.

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It contains symbolic
debug symbols to help you

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with your kind of
diagnostic debug sessions.

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Okay, well let me do that.

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I'm running Windows

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so let's run the Rust
compiler on my machine.

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Okay, so here we are.

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I've opened the folder.

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I've opened the command
window in the right folder.

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So let me just run the Rust
compiler, hello_world.rs

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and it will generate, let's
see what it's generated.

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The executable application, which is great

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and the the PDB file as well.

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So that's great.

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So I could run the application.

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Now I'll just show you how,
look, if I had an error message.

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So if we go back in the code

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let's say I was a Python
developer and in Python

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instead of saying fn, you say def.

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So maybe I was thinking about
Python when I wrote my code.

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Okay and maybe I really
was thinking about Python

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and I had a colon instead

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of curly brackets because that's
how it would be in Python.

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So lots of errors here.

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I wonder what the compiler
would make of that.

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Let's try it again.

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Okay, so there's an error online one.

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Oh, that was a bad start.

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It's expecting some kind of simple

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the main function or this
is the scope operator.

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We'll have a look at that later.

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So it's clearly got confused,
but then look at this

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it gives me helpful error
messages, shock, horror.

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Maybe you should write fn instead

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of def to declare a function.

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Well, yes, maybe I should.

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So let's fix that, save it.

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Go back into command window and recompile.

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I wonder what we're gonna get this time.

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Oh dear, oh dear.

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It's confused about the the colon.

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It was expecting this colon
to be a curly bracket perhaps

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or maybe we'll have a look
at the syntax later on.

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The arrow syntax here is how
you can specify the return type

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from a function you could
select arrow int, for example

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if it was meant to return an integer.

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So it's got horribly
confused at this point.

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Usually when you get multiple
errors, you ignore everything

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apart from the first one.

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Fix that and then hope
that it fixes the others.

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So I realize that this is a Rust program

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not a Python program.

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I save the file and I recompile.

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And we're back in the room.

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So the application is ready to run.

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To run it, let's see how to run it.

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So to run the application

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if you are on Linux or
Mac, just run it like so.

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And if you run it on Windows like I am,

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then you just run it like that

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with a back slash instead
of a forward slash.

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So .\hello world.

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Of course I could say
hello world.xe on Windows

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but I don't need to.

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And it was well worth the wait.

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So hello world.

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Marvelous.

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Just a quick reminder, I
talked about this in the

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one of the earlier sessions,
the Rust Playground,

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an online editor where you
can play with Rust syntax

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without having to actually
install it on your machine.

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Most languages these days
have some kind of playground

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an online editor for you to have a play.

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So for Rust, this is the
Rust playground window.

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Let's have a quick look at that.

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So here it is.

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This is the code that was
actually in the Rust playground

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when I opened it.

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And it looks fine to me, so I can run it.

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In fact, I'll miss off a curly bracket.

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I'll have a deliberate error
here and I'll try to run it.

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So the compiler runs online

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and the error message gets report here.

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It's the same compiler, but in
an online kind of experience

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and it's complaining about
an unclosed delimiter.

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The curly bracket that started
here is not closed here.

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Oh, I see what I've done wrong.

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I forgot my curly bracket.

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Let's try that again.

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The compiler when you do
online can be a little bit slow

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because it's kind of
like a remote experience.

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So you have to be a little bit patient

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when you're running it.

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So I'm just gonna wait
for it to be compiled

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and it has compiled successfully.

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And here's the output
from the application.

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Okay, so I'm not going to be
using the playground a lot

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during the demos

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because the code we've got
is gonna be more significant

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and we'll kind of do it properly.

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But if you haven't yet got
the compiler installed,

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you can always try examples
here just as a starting point.