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Hey, guys.
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Welcome to another episode of Swift Deep Dive.
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And in this lesson, we're going to talk about IF and ELSE statements,
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also known as conditionals.
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So the idea here is what if you could check for a condition, and based on whether if that condition is
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true or false, then you would perform different actions.
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So in this case, if the green light was on, then the car should go. But if the red light was on, then it
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should stop.
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So we can also express this in code
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like so.
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So here we're checking if the traffic light is equal to green, then we will perform the action of go,
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otherwise, namely if this is false,
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namely if the trafficLight is not green, then we will perform the action of stop.
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Now, similar to what you saw with functions, curly braces often contain more than one line of code. So
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more frequently, you'll see this formatted like so. Now, that's all very well and good, but in a lot of
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cases, especially in code, it's not always just true or false, because here our conditions, whetherif the
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trafficLight is equal to "green," it can only be true or false, it's either green or not green.
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So we only have our "if" and our "else" blocks. But in real life as with code, there's often other possibilities.
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So what do you do, for example, if the traffic light was amber? Then we might have to adjust our code a
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little bit to take into account this third condition.
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So I'm not sure about the "Highway Code," but at least when I drive, if it's amber, I just press the gas
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pedal. And just as long as there's nobody on the road, I just go. Now, don't trust my word, read the "Highway
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Code."
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But if we convert this condition to code, then we're saying that if it's green, then definitely go.
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Else if the traffic load is equal to amber,
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so we're tagging on another condition here,
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well, then in that case, use your judgment. And then the final "else" is if all of those are not true, then
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we're going to stop. In programming,
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we call these conditional statements because we're performing different actions based on different conditions.
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So here's a challenge for you.
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I want you to either open up your previous eyes with playground and delete everything inside or simply
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just create a new playground. In that playground,
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I want you to create a function called loveCalculator. Inside the function, generate a random number
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between 0 and 100, and then store that number inside a constant called loveScore.
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Now, if the love score happens to be equal to 100, then I want you to print "You love each other like Kanye
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loves Kanye."
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Otherwise, I want your code to print "You'll be forever alone."
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Then finally, call the function so that you get a message showing up in the console. And 99 out of 100,
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it's probably going to say, "You'll be forever alone."
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So feel free to modify my messages as you wish.
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So basically, you'll have two messages and depending on the condition of the love score, it will trigger
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either one of those messages.
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So pause the video and try to complete this challenge.
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All right.
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So the first thing we're going to do is create a new function which we're going to call loveCalculator.
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And then inside this function, we're going to create a random number generator.
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So we're going to generate whole numbers,
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so they're going to be integers, and then we're going to use that random function that we saw before
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in order to generate those numbers.
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Now, if you forgot any of these parts,
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be sure to just simply do a quick Google, do a quick search on StackOverflow, and you should be able to find
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these bits of code relatively easily.
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You don't have to memorize them.
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And inside are random number generator.
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We're going to provide a range.
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So I want to generate numbers between 0 and 100.
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So now we've got our random number, we have to hold it within a container,
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right?
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So we're going to store it inside a constant and we create constants with the "let" keyword
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and then we're going to name it
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loveScore,
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and then we going to set it equal to the right-hand side which is, of course, going to be a random number
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between 0 and 100.
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Now that we have our random number loveScore, we're going to use our If statement that we just learned
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about.
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Now, if you want to get a starting structure, you can actually simply type "if." And on the left, you've got
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this little code snippet symbol.
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Then if we hit Enter, it'll insert our code snippet.
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So it shows a placeholder for our condition that we're checking,
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and then finally, for our code that needs to execute if that condition was true.
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So our condition, in this case, is whether if the loveScore that we generated is equal to 100.
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Now, notice that there's a big difference between two equal signs and one equals sign. Two equal signs
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means that we're checking if the left-hand side is equal to the right-hand side.
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So this entirety is going to be a condition that's going to be true or false.
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And if you want to see what this is actually going to be equal to, then feel free to try and print it,
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then you can see that this will be true or false.
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So this double equals means checking if left-hand side equals right-hand side. A single equals means
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make the left-hand side equal to the right-hand side.
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So it's assignment versus checking.
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Now, we've checked if the loveScores equal to 100. Well, then, in this case, the code that should execute is
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a print statement that says, "You love each other like Kanye loves Kanye," which is a lot.
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Now, if they get 100, that's what's going to print.
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But then we're going to add an "else" statement to trigger
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if that was not true.
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So if the loveScore was not equal to 100, then in this condition, we're going to print "You'll be forever
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alone."
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Cool.
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So now the final thing to do is to actually call our function loveCalculator, so that we actually trigger
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the running of this function. And if we hit play, it will say "You'll be forever alone." because the score
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that got generated was 23. And you can click play a number of times to see some different scores.
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Now, it's going to be pretty unlikely that I'll ever be able to reach 100. So that, I'm not going to try.
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But this is essentially the solution to our challenge. So we've seen the "Is equal to" check,
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but there's actually a whole bunch of other checks we can make as well, whether if something Is not equal
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to is an exclamation mark and equal sign, whether something is greater than, or lesser than, greater than
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or equal, lesser than or equal to.
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So you can use all of these different comparison operators to compare the left-hand side and the
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right-hand side. And then the end result is a condition that will still be true or false which determines whether
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if your "if" statement gets run or if your "else" statement gets run.
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Here's the second part of our challenge.
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I want you to modify the loveCalculator, so we'll get our "You love each other like Kanye loves Kanye" message
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trigger more frequently. And it should print that message
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if the love score is greater than 80. Otherwise, if the love scores between 40 and 80, then it should print
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"You go together like Coke and Mentos."
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And finally, if the loveScore is less than 40, you should print "You'll be forever alone."
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So go ahead and try to make those modifications to your loveCalculator and complete the challenge
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now.
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All right.
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So all we need to do here is to change our condition here from checking whether if loveScore is equal
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to 100, to whether if it's greater than 80. And then we're going to add that "else if" which checks for
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the next condition.
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So else if loveScore is greater than 40,
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and in this condition, we're going to print "You go together like Coke and Mentos." Cool.
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So now finally, there is the final "else" statement which will catch everything else and including if the
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loveScore was not greater than 40, and not greater than 80. So this is the solution to our challenge.
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Now, if you're wondering how our code actually flows, then let's think about a couple of example numbers
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that we might generate.
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Let's say that we generate 55.
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Well, the first condition checks if loveScore is greater than 80,
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so that's going to be false.
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So we're going to skip that one. And then the next condition to check is going to be if the loveScore
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is greater than 40, which is true, 55 is greater than 40.
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So it's going to do this block here. And then once it's done, it's going to complete,
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and that's going to be the end of the running of our function.
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Now, let's say that we had a higher score that we generated. Say, we generated an 85.
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Well, in this case, loveScore is indeed greater than 80.
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So "A," this block will trigger, and then it's going to skip checking all of the other conditions because
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these conditions have an "else" in front of it.
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So it reads kind of like English. Well, if loveScore is greater than 80, then do A, else,
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so namely if this was false, then check this, else, do this.
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So none of these "else" statements will trigger because the original "if" statement is already true and has
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already been triggered.
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So here's a bit of a brain teaser.
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What if instead of having an "else if" here, I replaced it with an "if"?
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What do you think would happen in this case?
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Pause the video and have a think about it.
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And if you want to see the solution, just change your code in your playground, and you'll be able to check
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whether if you managed to predict the outcome correctly. The difference between the "else if" and the "if"
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statement is that, in this case, we're going to check if the loveScore is greater than 80, which it is,
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so it's going to do "A." But then because there is no "else" that's coming up, it's going to check the next
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condition which is whether if loveScore is greater than 40, and 85 is indeed greater than 40.
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So it's gonna do "B" as well before it retires.
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So in this case, because we don't have the "else if," it means that it's going to check all of the conditions
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with an "if."
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But if you have an "else if," it means it'll skip it as long as the previous one or one of the previous ones
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were true.
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Now, the final thing that I want to show you is that you can also use these combinations where you can
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combine these checks so that you can check if two conditions are both true or if one of the conditions
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are true or, finally, if something is not true.
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For example, in terms of our loveCalculator, we could also write the code like so, right?
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We could say that if loveScore is greater than 80, then do A.
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And then we could use an "if" statement that checks if loveScore is greater than 40 and it's less than
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or equal to 80.
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So between 40 and 80, well, in this case, it's going to do B.
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So now even though we still have two "if" statements like before, this time it's actually only going to
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execute one of these blocks, because even if the first one was true and it's going to do "A," it's going
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to continue and check the next one. But the next one is actually not true anymore because loveScore
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85 is indeed greater than 40. But this condition also requires that loveScore must be less
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than or equal to 80. Because one of these is not true,
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therefore, this condition overall is going to be false. And you can have a go at changing the conditions
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in your playground to use the "and" or the "or," and the "not" to see how each of these work.
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So now that you've learned all about the Swift conditional statement, the "if," the "else," and "else if," then
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it's time to complete the IF/ELSE assignment. 
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.