Tinkering with Perl

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If-then

Remember, back when we introduced statements, how we talked about going to a friend's house? Let me reproduce the list of what to do:

Ask your parents for permission to visit your friend.
Call your friend's house, and ask permission to come over.
Finish getting dressed.
Walk over to your friend's house.
Take chewing gum off of your shoe.
Greet your friend.
Play with your friend.
Eat a snack.
Play some more.
Say goodbye.
Walk home.
Take off your shoes.

Well, this list didn't involve any decisions -- and there are decisions involved. For example, you only continue over to your friend's house if you get permission, right?

Let's rewrite the list using if-then logic:

Ask your parents for permission to visit your friend.
If your parents give permission to visit your friend:
    {
    Call your friend's house, and ask permission to come over.
    If your friend's parents give permission to come over:
	{
	Finish getting dressed.
	Walk over to your friend's house.
	If you stepped on some chewing gum:
	    {
	    Take chewing gum off of your shoe.
	    }
	Greet your friend.
	Play with your friend.
	Eat a snack.
	Play some more.
	Say goodbye.
	Walk home.
	Take off your shoes.
	}
    }

What we have here is a modified list of how to visit your friend, that only does things if they are appropriate -- for example, it only goes over to your friend's house if you have permission to go over.

The syntax in Perl (how you tell the computer to do something) is as follows for this sort of thing:

if (condition)
    {
    code to execute if condition is true
    }

"if" must be spelled exactly that way, with a lowercase 'i', and the curly braces put around the code to be executed. What Perl will do when it sees that, is see if the conditional clause is true, and if so, execute the block that's inside the braces.

Tinkering with Perl

If-then

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