Welcome to learn swift programming for beginner's lesson one.

Today we're gonna talk about variables.

You're gonna learn about what they are had to declare them and swift code, and furthermore, how to use them.

All right, so let's get started for the rest of the lessons in the Siri's, we're going to be working inside this app called X Code X Code is the tool that Apple has provided for people to build APS with and inside X code.

You're gonna be able to create your user interfaces.

You're gonna be able to write the code to express the logic in your app.

You're gonna be able to test your app.

Even so, that's why this is where we're going to start in learning Swift.

We're gonna be writing this swift code inside the app that you're actually owned to use to build ups with in the future.

So this is where you're gonna get X code.

Just go to your browser, go to developer dot apple dot com slash ex code.

Or you can launch the Mac app store on your computer and search for X code there.

If you're on the Web page, you can see that there's this big blue download button up top.

Now, Ideally, you want to make sure you're using the latest version of X Code, and right now, as of this recording, it's eight, and you can check your version if you go to X code.

Ah, you can see it here in the welcome screen.

And you can also go up here two x code about X code, and you can see what the version is.

If you are a PC user in your running windows, there may be some additional work you need to do before you can run X code.

Or you might have to use an alternative solution to build IOS ups.

So check in the description below for PC solutions.

However, if you are a PC user, don't let that discourage you.

Uh, for me.

Personally, I lost about 2 to 3 years of learning Iowa's developments simply because I didn't have a Mac and I didn't want to get a Mac.

But these days there are alternative solutions.

You don't actually have to buy a Mac computer, although I eventually did.

And now I haven't looked back s O.

Anyways, now that you have X code, and after you've installed it, it's a pretty large install.

It's pretty big program, so I might take some time.

But after you have it installed and you launch it, you're going to see this welcome screen.

You can see here that when you want to create an app for iPhone, iPad, Mac er, whatever you're going to go to create a new X Code project, and that's going to start a full out project for you to build a nap in.

But here, we're going to start a new playground because that's going to allow us to type some code quickly.

It's gonna let us run that code and see the results, and we're not committing to building in a project.

It's simply like a sandbox or a playground, as it's named.

Now, if you don't see this welcome screen, what you can do is just go up to file Neil and hit Playground right there, and that's going to start a new playground for you as well.

Or you could just hit this button, get started with the playground, so that's gonna launch this dialogue for you, and I'm simply going to leave the default name their platform should be Iowa's, and I'm going to save this on my desk cop.

Okay, so after your playground runs, you'll see up here, it's doing a whole bunch of stuff.

Ah, launching Simulator, getting it ready.

And when it's done all that, it's going to say, Ready?

You can already start typing in code.

So there you go.

It says, ready.

But when it doesn't say ready and it's doing something, then chances are whatever you're typing here is not going to show up on the right hand side.

Okay, we're gonna start with a quick tour of this playground window here.

So down on the left hand side, I have a bunch of line numbers.

Now, if you don't have these and you want them, they can be useful at times, especially when I'm teaching and I need to refer to line numbers.

You can go toe X code preferences, and you can go to text editing, and you can simply enable line numbers there.

Now, this area right here is where we're going to type our swift code, and it's already got a bunch of stuff for us right here, which we're going to go through in a second on the right hand side, you're going to see a quick preview of the results of what you type there.

Now, a lot of people have trouble with getting output to show up on this right hand side based on what they type here.

Um, well, one of the things that you can check is just in this status bar up here.

Make sure that it stays ready.

And as your typing something.

Let's say I change something like that.

You're going to see that it for a brief second there there was a little spinner because it's evaluating your code here.

Um, if you wanted to show up, just make sure it's as ready to process your next command.

And, you know, you should see that output there.

Alternatively, there is a trade down here which you may not notice because it's hidden.

At first, you can hit this button to show that the bug area, or there's also this little button here to hide the different panels.

Okay, but we don't need to see all of that, but this debug panel may be useful.

Ah, when we start to output things here, this is called a console area where we can use swift commands to output things.

This blue icon here is to execute the code in your playground.

So if you can't get things to show up on the right here, try clicking this button to run your playground.

Right now it's blue because you can see there's a little drop down arrow there.

If you click and hold it, you can see whether you want to switch it to automatically run.

And that's going to run the playground whenever you type something, or you can set it to manually run and you can see now it's great out.

So if I type in some new code, it's not actually going to change or display what I have on the right hand side here.

Unless I click the play button to run it, so I would recommend to have it set toe automatically run.

So now that you know the main areas of the playground, let's get into the meat of today's topic variables.

And in fact, what we have here is a variable in swift, a variable hold some data.

Now this data could be a value.

It could be a reference to an object, or it can even point to a function which are things that will get into the future.

But for now, we're going to say that variables hold data.

Now, as you can see from this example, line of code a variable has a couple of distinct parts.

Let's break it down.

Variables need to be declared before they can be used.

So this var key word is used to declare a new variable following the var keyword.

You have the variable name in this case, it's S t r.

And really that's it.

You've declared your new variable.

So it's got the var keyword and it's gotten to variable name now taking a look at the whole line.

What we have on the right hand side there, that's some data.

We did say that variables hold data right in that equal sign in between the variable name and the piece of data.

Well, that's an assignment operator.

So what we're doing in this line of code is we're declaring a variable called str and then a signing that piece of data to that variable.

So now jumping back into the playground, let's see the effect of that I can say something like print, which is a key word that is going to print something to that console area down below.

So if I say print and then in the parentheses I put str you can see that it's printed that hello?

Play out s rough lying down there on the right hand side.

We can see a quick preview of that and notice that there's a slash end here.

And that is basically, um, just denoting that there's a new line associated with that print statement because, ah, the next time I print something, it's gonna be printed on the next line.

So you don't see that here because a new line is just, um, a carriage return or white space.

You can't really see it, but in here in this preview, it's visualized as that slash and which is just a new line.

So let's take a look at a couple of different pieces of data that we can store into variables.

So I'm going to declare another variable here called a, and I'm going to assign a number into it.

So just bar one and I mean it clear another one called B, which I'm also a sign one, and I want to show you that you can perform operations between the variables or on the variables.

So, for example, I can save print A plus B, and you can see here that the result in the consul here is to now notice that what I'm using the variables in an equation or an operation like this I don't need to use the key word far, because that's only for declaring variables, right?

So this little part is declaring the variable, but when you use them afterwards, you just need to refer to them by name.

So let's try some other things.

Print a minus B imprint.

A times be okay, so variables hold data and you can perform operations on variables.

Now you can change the data that the variable is holding so I can say something like a equals two now, right?

In fact, actually, let's not do it down here.

Let's do it here after we've assigned one into a let's say, a equals two, and as a result, you can see all of these operations have changed because a is now too.

So a plus B is three a minus.

B is one and so on because A is now to now when you assigned something into a a different piece of data, it replaces what it was holding onto before so is no longer one.

It is now too.

But notice how when we assigned a new piece of data into a we don't have to write bar again.

That would cause an error because we've already declared that variable up here and memory in the system has been allocated to it.

And so we don't need to re declare it.

All we need to do is a sign new data into a like that.

Now, if you're playing around in the playground yourself, you may notice something like what?

If you try to assign something into str like one?

Well, you're gonna get an error and that's because of something called data types which we're going to learn about in the next lesson.

But for now, just know that for str because we've assigned some text into it up there.

If we want to reassign some data into it again, it has to be text us well, so that would be valid.

Furthermore, you can also a sign variable as another variable so I can say a equals B down here and in that case, a wood now equal one again.

Well, it was one to begin with, So So let's say I did that.

So if it was too and then I said a equals B, then now they would both be one.

Now, before we move on a quick note on naming variables Here we have a variable str and I've named some variables A and B so normal you want name variables like A and B because they're not descriptive of the data that they hold.

So if you're going to be using variables just like this in an operation, when it be easier if you knew what a represented in one be represented while you can declare your variables using any sorts of names that you'd want but you can't put some special characters and you can't put spaces in your variable name.

However, the common practice is to use a form of camel case where the first letter is lower case.

So let me show you what I mean, so I can save our And if I want to describe my valuable if it represents, um let's say the number of apples that I have.

I would say something like my number of apples like that, and you can see that each new letter of each word is capitalized except the 1st 1 Now you don't want to get too crazy with the length of the variable name as well.

And you don't want to go too short, so short that it doesn't actually mean anything.

So there's no right or wrong answer or hard limits.

It's based on, you know, your own preference.

And it's more important if you're working in a team with other people that you agree on a certain coding style because you're both going to be working on the same code.

Okay, so one more thing.

I want to talk about our Constance so they are like variables, except that once you assigned something to them, you can't reassign data into them.

So that's really the only difference.

That and also how they're declared.

So with variables, use the keyword var.

But with Constance, you use the key word let so I can say let C equals 10 and then down here.

If I try to reassign something in to see like that.

X code is not gonna like that.

It's gonna throw in error, and it's gonna tell you with this red dot down here, and if you click it, it's going to say cannot assign value to see because it's a let constant.

Now it gives you this little bubble here and what you can click and smartly, it's gonna change.

Let Tobar because it senses that you want to reassign data into it.

So you might ask, Why would I ever want to use a constant if it's more limited in its functionality, Right.

If I declare everything is variables, then I have all the flexibility I had one.

While there are a couple of reasons why you'd want to use constants when it makes sense.

For one thing, it helps the computer work a little more efficiently because it knows exactly what that constant will be.

And that's not gonna change.

But more importantly, it's that for you as a coder, you know that that constant isn't going to change, because when you're building your up, you're gonna have a lot of variables.

And when you have some sort of issue in your app and you don't know why it's happening in your tracking down your code or tracing it line by line, and you're trying to see if maybe at some point you've accidentally assigned something to a variable, and that's throwing off.

All your calculations are all over your logic.

It's going to be a nightmare to try to solve an untangle.

So if something you know it isn't gonna change, you can assign it to a constant.

And then when you're looking through your code, you can be sure that the issue doesn't lie with that constant because you know what can't change.

Okay, so that's it for this lesson on variables.

I hope you're practicing on your own computer with X Code and check below this video for a link to the cheat sheet and the notes.

Hello, Welcome to learns with for beginner's Lesson two.