ActionScript for Flash MX: The Definitive Guide, Second Edition

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Chapter 5: Operators

expression month != 0 && day != 1 would exclude our users on the first day of any

month, not just January 1. This is hardly what we intended.

It’s much easier to check if today is January 1:

month = = 0 && day = = 1

This expression yields true only on the first day of January. Once we’ve gotten that

far, all we need is the NOT operator to determine when today is not January 1:

!(month= =0 && day= =1)

Obviously, this code’s intent is much clearer than the month + day > 1 test used in

Example 5-5.

Another typical usage of the NOT operator is to toggle a variable from

true to false

and vice versa. For example, suppose you have a single button that is used to turn

the sound on and off. You might use code like this:

soundState = !soundState // Reverse the current sound state

if (soundState) {

// If sound is turned on, make sure sounds are audible

} else {

// If the sound is off, set the volume to 0 to mute it

}

Notice that ! is also used in the inequality operator (!=). As a programming token (i.e.,

symbol), the

! character usually means not,oropposite. It is unrelated to the ! symbol

used to indicate “factorial” in common mathematical notation.

The Grouping Operator

Aside from being used in function calls, parentheses—( )—can also be used to group

a phrase of code to override ...