HTML, XHTML, and CSS All-In-One Desk Reference For Dummies®

Chapter 4. Control Structures

In This Chapter

• Getting familiar with if-else conditionals

• Using switch structures

• Working with while and for loops

• Using comparison operators

Control structures allow you to make decisions or control the order of execution of your program. if-else conditionals, case statements, for loops, and while loops are all control structures.

Introducing if-else Conditionals

If you have two or more courses of action to choose from in your program, a perfect way to handle this is through if-else conditionals.

if conditionals

The simplest form of a control statement is the if conditional, also known as an if statement or an if construct.

An if conditional evaluates an expression down to its True or False value. If the value is equal to True, some code will be executed. If the value is False, the code won't be executed.

Here's how you construct an if conditional:

1. Start with if.

2. Follow this with a condition expression in parentheses, ().

3. Follow this with the code to be executed if the expression is met.

This code must be surrounded by curly braces.

The simplest form of an if conditional uses a variable that you expect to contain the value True or False (known as a Boolean variable) as the expression to be evaluated by the if statement:

$expression = true;

if($expression){
    print "true!";
}

This code would print true!.

If you wanted to check $expression to see if it was equal to False, you could precede it with an exclamation point:

$expression = true; if(!$expression){ print "false!"; ...