Conditionals

The if..else conditional statement allows you to test a condition and execute a block of code if that condition exists, or execute an alternative block of code if the condition does not exist. For example, the following code tests whether the value of x exceeds 20, generates a trace() function if it does, or generates a different trace() function if it does not:

if (x > 20) 
{ 
    trace("x is > 20"); 
} 
else 
{ 
    trace("x is <= 20"); 
}

If you do not want to execute an alternative block of code, you can use the if statement without the else statement.

You can test for more than one condition using the if..else if conditional statement. For example, the following code not only tests whether the value of x exceeds 20, but also tests whether the value of x is negative:

if (x > 20) 
{ 
    trace("x is > 20"); 
} 
else if (x < 0) 
{ 
    trace("x is negative"); 
}

If an if or else statement is followed by only one statement, the statement does not need to be enclosed in curly brackets. For example, the following code does not use curly brackets:

if (x > 0) 
    trace("x is positive"); 
else if (x < 0)  
    trace("x is negative"); 
else 
    trace("x is 0");

However, Adobe recommends that you always use curly brackets, because unexpected behavior can occur if statements are later added to a conditional statement that lacks curly brackets. For example, in the following code the value of positiveNums increases by 1 whether or not the condition evaluates to true:

var x:int; 
var positiveNums:int = 0; 
 
if (x > 0) 
    trace("x is positive"); 
    positiveNums++; 
 
trace(positiveNums); // 1

The switch statement is useful if you have several execution paths that depend on the same condition expression. It provides functionality similar to a long series of if..else if statements, but is somewhat easier to read. Instead of testing a condition for a Boolean value, the switch statement evaluates an expression and uses the result to determine which block of code to execute. Blocks of code begin with a case statement and end with a break statement. For example, the following switch statement prints the day of the week, based on the day number returned by the Date.getDay() method:

var someDate:Date = new Date(); 
var dayNum:uint = someDate.getDay(); 
switch(dayNum) 
{ 
    case 0: 
        trace("Sunday"); 
        break; 
    case 1: 
        trace("Monday"); 
        break; 
    case 2: 
        trace("Tuesday"); 
        break; 
    case 3: 
        trace("Wednesday"); 
        break; 
    case 4: 
        trace("Thursday"); 
        break; 
    case 5: 
        trace("Friday"); 
        break; 
    case 6: 
        trace("Saturday"); 
        break; 
    default: 
        trace("Out of range"); 
        break; 
}