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Hey, guys, it's Angela again.
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Welcome to another episode on Swift Deep Dive.
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And in this Deep Dive, we're going to cover Swift Switch Statements.
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Now, if you were a train driver and you were pulling into a large station, say, Paddington or King's Cross
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and you had to manually check if every single platform was empty or if it was occupied, that would take
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you a long time.
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And that's kind of like trying to write an "if else" statement for a whole bunch of conditions.
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What's way more efficient and much easier is if you could just ask the station manager which platform
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should I pull into and they give you a number,
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1, 2, 3 or 4, and you just go to that platform.
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So this is kind of like how Switch Statements work.
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We can have a variable, say, if we think about our Egg Timer, we have this variable called hardness which,
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of course, depends on the button that the user presses on, and we can check to see what the value of that
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variable is equal to. If it's equal to "Soft," then we could print (5) or the Soft Time, if it's equal to
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"Medium," then print (7) "Hard," print 12.
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So, essentially, what's happening here is we're matching the value of this variable to each of these cases
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and depending on which one matches, then we're going to perform different actions.
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And finally, at the end, there is a default statement in case none of our cases match the current value,
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so usually that's where you might print "Error," where you might say, "None of the values match," or "Hey, you
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might want to check and see what's going on here," or you could use it like an "else" statement, like a catch
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all, do this in all other cases.
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Now, the reason why Switch Statements are so great is because not only do they reduce the amount of code
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you have to type. Instead of having to type if hardness is equal to "Soft," open brackets, close brackets,
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if hardness is equal to medium etc..
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But underlying how a Switch Statement versus how an "if" and "else" statement works, if you have more than 5
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cases, it's usually more efficient to use a Switch Statement because it performs a search rather than
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having to manually go through each of the conditions and check them. If you have less than 5 conditions,
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then it's often quicker and easier to write just some "if" statements.
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Now, what if you can't match the precise value of a variable?
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What if you wanted to match a range, say, if hardness was actually a number and we wanted to check if
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it was between, say, 3 and 5, and then 5 and 7?
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What would you do in that case?
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Well, here's where the Swift range operator comes in again. And we saw this already before, we saw that
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you could use three dots to create a closed range where you're creating a range between "a" and "b."
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So, for example, we could create a whole bunch of random numbers between 1 and 100, including 1 and 100,
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then we would use the close range, and then we have the half-open range where we have a less than sign
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at the end.
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And this means that we have a range between "a" and "b," but not including "b."
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And finally, one that you haven't seen yet is something called a one-sided range operator where you leave
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one of the sides either the "a" side or the "b" side empty.
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So this means that we're creating a range that is up to and including "b," but it can be any number that's
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less than "b."
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So bearing in mind what we've just learned,
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I want you to challenge yourself and play around with these range operators as well as the Switch Statement
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by changing our existing loveCalculator that you created using an "if,"
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"else if," "else" statement into one that uses a Switch Statement only. So have a think about what you need
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to do, maybe rewind and take a look at the range
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operators
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if you need to, or Google for the range operator in the Swift Programming Language book and have a read
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over there.
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But essentially, the challenge is to simply adapt your loveCalculator
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that's using an "if" statement into one that uses a Switch Statement.
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So pause the video and try and give that a go.
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So here I've got the code from before where we're using our "if," "else if," and "else" statements to check if each
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of these conditions are true and perform the correct actions.
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Now, in this case, we're going to change it to a Switch Statement.
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And, again, I'm going to use the capability of Xcode to provide code snippet by just starting out with
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writing the keyword which is, of course, "switch," and I'm gonna hit enter, and then insert a code snippet with
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these placeholders for me to replace.
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So, in this case, the value that we're checking or we're switching on is, of course, our loveScore.
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So that goes there.
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And then the case or the pattern that we're matching is whether if loveScore is greater than 80.
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So in this case, I'm going to check if the loveScore is greater than 80.
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So to do that using the close range operator, we would write 81...100.
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And in that case, the code that should get executed is, of course, this line, printing
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"You love each other like Kanye loves Kanye."
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Now, in order to add another case, I'm simply just going to write the word "case," and then I'm going to
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provide the case pattern that I'm trying to match.
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So in this case, we'll need to check if the loveScore is greater than 40, and less than or equal to 80.
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Let's use the half-open range operator this time, so that
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I'll write
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41..
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less than 81.
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So in this case, what we should do is to print "You go together like Coke and Mentos." And the last case
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I'm going to add is if it's between 0 and 40. Let's use the one-sided range operator this time by writing
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...40.
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And finally, we're going to print "You'll be forever alone."
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Now, the default statement should catch if loveScore was ever outside of this range.
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And because we're creating a random number here between 0 and 100, it's really unlikely that it's ever
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going to go outside of our three Switch Statements. And if it really doesn't, then we should print that
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there's an error and love score is out of range.
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And that's my sample solution to the challenge.
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Now, your code might be slightly different and you might have used slightly different range operators,
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but as long as you print the same output as with the "if else" block, then your solution is correct. So
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here we've created our Switch Statement and it replaces our
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"if" and "else" statement. Now, in this case, it might seem like we're actually writing a bit more code than before.
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But if you had a lot of cases, say, 5 or 6 or 7 or more, then it would be a lot more efficient
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writing it like this, and your code will also run much faster than if you just had a whole bunch of conditions
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which each need to be checked and confirmed. Instead,
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this case, we are pattern matching the value of this against one of these cases and it's more performant
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when there are a lot more conditions.
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.
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.