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Welcome back.

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This video, we are going to look at Collins when expressions, which is a replacement force, which

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statements from other programming languages such as C, C++, E Sharp Java and many others.

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So if you have never seen any switch statements yet, no worries because it's something that is similar

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to what we are going to build in this video.

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And it's just what is used in other programming languages, but it's a more compact and more powerful

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tool than to switch statements of those other programming languages.

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So let's go ahead and use it, and therefore I'm going to go ahead.

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And by the way, our IEEE already said, Hey, why don't you use it when expression here?

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So when we use this if age?

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So and so it's it's a better way would be to simply use a when expression or simplify this expression.

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Of course, I could do that directly here.

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And the idea would do everything for me, but I want to build one myself, so I want to build a when

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expressing myself.

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Therefore, I create a new variable called Season and it's going to be season three.

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I I'm going to set the season to three and then I have a one expression, so I use this one keyword.

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Then the brackets and then the variable that I want to look at, because here I specifically look at

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a variable.

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Let's say I look at the season and depending on what the value of season is, I want to execute specific

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code.

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So let's say a season is one, then I want to execute the code, which just says it's spring.

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Then if season is two, I want to execute the code that is going to be summer.

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So you can see the structure is the value, then an empty space and then minus greater sign and afterwards

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the code that you want to execute.

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Now, of course, you can also go ahead and execute a multi line code, so it doesn't have to be a single

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line code.

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And here I'm just going to say print out and fall or print alone or in this case, both print and.

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Autumn, and then of course, we have our final season, which is winter.

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All right.

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So print, Alan Winter.

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So what is the default case?

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So the case that should be executed if none of the above is true.

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So if season is neither one nor two or three, No.

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Four, well, then we can execute the Owls blog with the Owls keyword.

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All right.

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So here I'm just going to say invalid season.

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So at least on Earth, we only have four seasons.

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So let's say we were on another planet.

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Maybe there were more seasons.

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But these are all the seasons that we have.

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So this is in general how we go about using when expressions.

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So you have a variable that you look at doesn't have to be an integer.

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It could be a string as well.

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But we are looking at a variable.

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And then depending on the value that we have, we execute some code.

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Now the cool thing is we can go ahead and do a slightly different approach to this as well.

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So I'm just going to go ahead and say I have a month instead of a season.

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So here the month will also be three.

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But now when the month is one, then we, for example, have winter.

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Two is also winter, three spring for the spring, five for spring and so forth.

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So each season has three months.

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So now we can go ahead and do as we used to when you were again in the brackets, we say which variable

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we want to look at.

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And then in the curly brackets, that's where our code, our execution code will be, where we check

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the different states.

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So let's say I want to.

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Execute three dot dot five.

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So in those months or months of three to five, I want to print.

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Spring, then in six.

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Until 8:00, I want to print.

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Summer.

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So you see a very similar approach, only that now we're not looking at just one value, but we're looking

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at a range of values here.

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The ranges from six to eight.

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And then, of course, we can also go ahead from nine to 11.

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So Print Island Fall.

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All right, but now what do we do with winter?

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All right.

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We cannot do something like in 12 days start to.

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Parental and winter, because if you hover over it, it says, did you mean to use down to?

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Because it says this range is empty?

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Well, we could try down too.

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But now what it will do is it will go from 12 down to two.

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And we had those cases here already.

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You can see that if you want to go a range down, you can use the keyboard down to.

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But what I want to do is actually have the values 12, one and two, so I can do it like that.

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I could just say, OK, if those three values are true or if the month is one of those three values,

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then please go ahead and just print the long winter.

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And then, of course, our case, we can just use the same as we did before, so else, print of an

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invalid season.

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And now if we execute that?

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Then we will see its fall autumn, and then finally, we have spring because month three is March and

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March will be spring.

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All right.

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Now a little challenge for you.

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Please rebuild.

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What we had here.

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But do it with a weekend statement or one expression, but don't just use the autocomplete feature here,

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OK?

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All right, so I hope you tried it.

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So what we need to do is, of course, go ahead and use one page.

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And now we have two different cases, so let's say somebody is 21 and above, so we can use 21 dot dots,

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let's say 150, because no one is older than this age.

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Of course, we need to use two in key words.

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So let's say in that range, if the values in that range don't, please just go ahead and print.

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You now may drink in the U.S. by drinking.

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I mean water, of course.

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Then in 18 to 20, we can say something like You may vote now.

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And 16 and 17.

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And here we don't need to key, actually.

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So let's get rid of those.

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We can just say you may drive now.

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And then finally, we have an ALS blog which says you're too young.

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So this is something that we can of course do, especially the one here at the top.

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But what if I don't want to write it like that?

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Because I just want to say if somebody is none of the below, so none of the less than 20 or 20 included?

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Well, what you can do is you can use this exclamation mark before the inky word and you just say,

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OK, if it's none or not within zero to 20, then run this expression.

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So what that will adjust to is it says, all right, if the person is less than zero.

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So younger than zero or older than 20, then execute this code.

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All right.

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So now you saw to use when expressions.

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Now I want to show you one more thing about when expressions because we also can use a keyword which

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is called is so.

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We have this verbal x, let's say, and it's of type any, so I specifically say that it's of type any,

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which means that it's of type, object and other programming languages.

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So if you know any other programming language just means that this is going to be of any type of type.

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All right.

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It could be any type.

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That's pretty much what I'm saying here, and I'm just assigning a value of thirteen point thirty seven.

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And now I can check.

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X for its type, so I can just say, if it is an integer, then please print something like X is an

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int.

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But if it is a double, then please print.

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It's a double.

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And then of course, of course, if it is a string printer and is a string.

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And finally, we also have this block here as well where we say, OK, print L and X.

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Is none of the above.

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OK, so this is something that you can also do using this is key word to check if it is of a certain

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type that can be very useful because sometimes you get data and you don't know of what type it is and

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then you want to execute code based on the type that the data is so that the variable is that you are

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looking at.

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All right.

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So if we execute this?

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We can see that it says thirteen point thirty seven is a double.

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Of course, it is a double because there is a point or a dot there, so let's say we would add an f

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here, which makes this a float value.

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So instead of double now it's going to be float.

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Let's see what we get because it should say is none of the above.

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So thirteen point thirty seven is none of the above, so it's neither a double nor a string nor an end

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while looking at one expressions, you can of course also use not is.

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So you can say something or not is double then is not a double.

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All right, let's run this again, just to see if this or else will be executed.

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And there it says thirteen point thirty seven is not a double because it is not of type double.

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It's of another type.

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But you can also see this is never printed because.

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The statement here is true.

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It's now could be of any type, except for end and double for this whole thing to be true.

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So let's just say we want to make this a string and see if this string here at the bottom will be executed.

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Let's see.

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If it says X or X is a string and it says X is not a double, so you see we have the same order here,

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it goes from top to bottom because this statement here is true.

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Actually, this one here, this one and that one, so those following ones will never be executed,

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even though this is in effect, a string because we added the exclamation marks around it.

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This is this string, in fact, but this code will never be executed because one of the above is already

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executed.

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All right.

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So for this, the same structure as we had when looking at if and else if all right, so always goes

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from top to bottom.

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So you see, when it's just an alternative for if but sometimes it's more convenient and more precise

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and dense.

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And it just reads when X is of certain value or type, then do something.

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So do whatever is after the arrow.