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It's time for yet another Swift Deep Dive. And in this Deep Dive, we're going to look at variables.
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So essentially we've seen that variables are simply a way of giving a name to a piece of data so that
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we can reference it in our code later on.
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We did that for our IBOutlets as well as our DiceNumber variable which we created from scratch.
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And the problem that it solves is really simple.
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Let's say that if I was to give you a phone number to remember. And I give it to you written down on
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a piece of paper.
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Now, if all I had on there was just a number, I know what my drawers look like.
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And if I have a single piece of paper floating around in there, after not even a day, I'll forget what
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that number was all about.
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So how can we make this better?
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How can we remember what this piece of data is about?
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We could associate that data with an actual label and give it a name.
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So we're essentially taking our data and labelling it with a name.
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Well, this is essentially a variable because if we needed that piece of data in the future, we can
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simply refer to the label name, which is "Angela", and it will be able to retrieve that piece of data.
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So we have to write a little bit more
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if we're creating this code. We have to add a "var" keyword, which tells the computer that we're creating
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a new variable. And then we add an equal (=) sign to tell the computer that on the right-hand side of the
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equals sign is the value that we're assigning to that particular variable.
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So you can essentially view creating variables similar to creating just a box,
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right?
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And you whack on a label which will be able to identify what's inside the box and you put some data inside
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the box. And now you can store it somewhere on a shelf ready for retrieval.
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And by looking at that label, you'll know what's contained inside.
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So if you need the data that's inside, you simply find the right box with the right label.
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Now, variables were made to be varied,
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right?
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=)
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That's the whole point.
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So we can simply remove the old value and put in a new one if we wanted to.
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And now that label name "Angela" is associated with a completely different piece of data. In the resources.
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for this lesson, you'll find a download link for the Swift Cheat Sheet that we've created for you.
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And this is just a handy reference guide.
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A lot of students like to print it out, to have it beside them when they're learning.
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And it's a way for you to be able to quickly refer to the grammar of the Swift programming language.
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So just as in English, we have our commas and full stops and they have meaning in the sentence. In Swift
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and other programming languages, we have certain key words like the "var" key word, which is used for creating
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variables or the equal (=) sign which is used for assigning a value to a variable.
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And this is a handy guide that you can always flip back to when you're completing challenges and when
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you're trying to write your own code.
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So the way that we create a variable is we start out with the "var" keyword, then we give our variable
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a name and then we assign it a value.
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That's the theory of it.
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But let's head into a playground and actually create some code from scratch.
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So let's say that we had a variable called "a" and we gave it a number, let's say 5. And then let's
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create another variable called "b" and let's give it a value of 8.
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Now, if I decided to print these values, so print(a) and then print(b). Now notice in this case, I don't
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have those quote marks around the a and b, because if I had that, then it would simply interpret this
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as a command to simply print the letter or the string "a" and that's what you see here.
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But if I actually want the value of my variable a, then I have to make sure that I'm putting it
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in as a variable name a and b rather than anything with quotation marks in it.
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I can make this a little bit fancier by adding some string interpolation.
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If you remember "The value of a is" and then I can add that backslash and put my variable inside some
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parentheses. And now I get printed,
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"The value of a is 5". And I can do the same thing for b, "The value of b is \(b)" and let's just make sure
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we're not missing that final quotation mark.
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And now we get "The value of a is 5", "The value of b is 8".
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So now that we've covered the theory of Swift variables, let's get a little bit more practice with
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Swift programming through a coding challenge.
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Now, as always, the challenges are.
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completely optional, but solving them will help cement the concepts that we've covered and make you a
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stronger programmer. Also figuring out and solving these little puzzles is going to be a lot of fun.
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So what's the challenge? Without changing these lines or changing these lines,
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can you swap the values of a and b? So that when these two lines execute, it will say the value of a
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is 8 and the value of b is 5.
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But here's the catch.
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You can't type a single number.
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So in your solution, you're not allowed to type a 5 or an 8.
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You have to figure out how to switch these two without simply assigning it with a different number.
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Because the easy way is to say "a" well now equals 8 and "b" now equals 5.
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And I will get that a is equal to 8 and b is equal to 5.
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And I've switched those two values around, but I have used a number.
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So for this programming challenge, we're going to be using code to achieve this.
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And you have all of the tools and knowledge to be able to do this.
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But you might have to think a little bit outside of the box.
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So this is a really, really common interview question that you will get as a programmer.
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And it just tests you a little bit in terms of your lateral thinking and whether if you understand variables
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well enough. I'll give you a few seconds to pause the video before I show you the model solution.
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All right, ready?
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Did you have a go at the assignment? And did you manage to get it right?
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Now, the trick to solving this puzzle is to simply create another variable.
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So let's go ahead and replace this line with our code.
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I'm going to create another variable called "c", and I'm going to set c to equal the current value of
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a.
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So at this point, c is going to be equal to 5.
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Now, next, we can set a=b
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Now, at this point, a is now equal to 8.
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And finally, we can set b to equal the value that's held inside c and so b now equals 5.
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And within our three steps, if we run our code, you'll see that a is now 8 and b is now 5.
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We've managed to switch these two values around in only three lines of code without needing to write
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any numbers, such as a=8 or b=5.
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I'll see you on the next lesson
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where we'll learn more about Swift arrays.