The if expression allows you to test an expression; if it returns true then the following expression will be executed. You may also use the else keyword, followed by an expression, which will be executed if the test returns false. Note that a block of code is an expression.

The following is the general syntax:

if (condition) exprExecutedIfTrue [else exprExecutedIfTestFalse]

Now, let's look at some examples:

if(age<18)
{
   trace("you are not an adult.");
} else
{
   trace("You are an adult");
}

I think it is obvious here what this block of code does. Notice that this code could have been written in the following way too:

if(age<18)
   trace("you are not an adult.");
else
   trace("You are an adult");

This can be interesting to know, as it can save some typing when the block has only one...