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So let's discover what variables are using an Xcode playground to open up Xcode, go to file new playground.



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Now playgrounds just let you mess around with basic code and give you the results instantly so you don't



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have to create a brand new iOS project or anything crazy like that.



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Hit next on blank and save it wherever you want to save it.



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So mine's going straight to the desktop.



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Now, let me resize this for you.



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And you'll see that Xcode has pretty populated some stuff in here.



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First of all, it's imported UI kit, which allows us to run certain things in the code.



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Don't worry about that for now.



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Imports will be part of the course as we go along.



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What I want to focus on is this thing vare SDR, VA stands for variable and all the variable is at its



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basic level is something that's stored in memory.



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In fact, everything in your program is technically a variable if you use that definition.



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So functions are stored in memory classes and objects are stored in memory.



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So they're technically variables, at least in my opinion.



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The next section is the name of the variable, so in this case, star, now SDR is an awful name for



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a variable because if I come back to this code in six months, I don't know what Star stands for.



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Do I?



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Neither do you.



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If I come to your code and I see that I'm liable to not want to help you with your code because nothing



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is obvious.



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So if I was going to give this a better name, I would call it something like welcome message.



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And then everyone knows what it is.



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But I'm getting ahead of myself there.



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I do, however, like to have students trained in naming things correctly so their software and code



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is readable anyway, back to the subject at hand.



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So we have a variable string or star, which is this thing surrounded by quotes and that is a string.



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A string is simply a collection of characters in order.



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So that is simple enough.



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Now where do we go from here?



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Well, what we can do, you see this little blue icon at the side, if you hover over it, if you hit



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play on that, you will see over on the right hand side.



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The result of what you're doing there now, this is currently running and now it displays hello playground.



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These things are much faster to run the second time because it's already compiled a lot of stuff in



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the background.



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So that just spits out our variable.



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Now, what if I want to spit out this variable in the console and I'll show you what that means in a



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second.



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But we're going to run something called a print.



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And if I press play on that, look what pops up at the bottom of the screen, we have Hello Playground.



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So that print statement prints things out for us, and you can use that to debug your programs as you



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get more advanced, so you'll print out this method isn't working or this error came back from the server



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or whatever it is, and the user doesn't see it, but use the developer will be able to see it.



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Right.



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Let's create another string.



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So var my let's create another string with an awful name.



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My string is equal to what let's call this ground.



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So actually a better name would be name, but we'll leave it as it is.



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Now how does Swift and iOS and Xcode and all the rest of it know that this is a string while we've put



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it between quotes.



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So that's how it knows.



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But we can tell it explicitly.



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By putting a colon and then the word string with a capital S. So that tells it this is a string and



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if I start typing that again, you look at that little handy hint that pops up string a Unicode string



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value, that is a collection of characters, like I said.



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OK, so you can explicitly tell it so there are two ways of declaring variables, really.



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One is implicit let the system guess what it is and the other one is explicit.



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Tell the system what it is you'll get used to.



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Which one to use as in when?



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Because it varies.



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Right.



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And I know lots of programmers who just let the system guess the whole time.



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I would say that decent programmers as well.



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OK, now, of course, we can do the same here, we can print my string.



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And if we run this whole lot, we should get what we need now, notice when you print my string, we



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get this backslash in at the end of my name there.



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Why is that?



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Well, that's the short code for a new line, what you call it, carriage return a break.



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So it goes to another line.



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That doesn't actually get printed out, as you can see down here in the console, you just get the word,



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but the new line is printed because the next print statement happens on a new line.



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Right, so that's how we implicitly and explicitly declare a variable.



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Now, why is it called a variable, do you think?



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It's not constant, it's not called the constant, there are constants, but not in this case variable,



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because it is variable.



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So I can change my name.



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To.



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Mike, because we can wipe whatever's in that memory space and put something new in it and allocate



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more memory if need be, I'm not sure we can allocate less memory.



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So I guess that's something to watch out for, right.



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So variables are precisely that.



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They are variable.



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Now, what are we going to do next?



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Well, let's look at the final category in here, which is the constant.



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Now, in lots of languages, we use the word const or perhaps even constant to define something that



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cannot change.



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So if I wanted my name to be set in stone, I would set it as constant, unchangeable.



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The way we do that and Swift is let.



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My name is Quilty.



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Can't even spell my own name.



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Grant, right?



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So that's perfectly fine, that will run, but if I run, my name is equal to Mike.



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Watch what happens.



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Just wait for the system to catch up.



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Cannot assigned to value.



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My name is a let constant.



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Right, because it is constant.



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Something of note for everyone, beginning programming their programming journey is wherever you can



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use a constant right.



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It's really good practice to keep things constant and to not modify variables on the fly unless you



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have to, because you do have to on occasion, in fact, maybe half the time.



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But constants mean that you don't have what we call spaghetti code crossing over each other.



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Everything's changing everything else.



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And then when you get a bug, it's really hard to track down.



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So constants are your friend, right?



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I'm going to set you guys a little bit of homework here.



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Now, what is it?



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I've got my notes here.



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Create a string variable with your name in it and print that string to the command line.



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So I want you to create a string that assigns your name to it.



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It can either be variable or constant.



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And then I want you to print that the command line.



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Off you go.