Learning PHP & MySQL, 2nd Edition

Chapter 4. PHP Decision-Making

In the last chapter you started to get a feel for programming with PHP and some code basics. Now it’s time to expand your comfort, knowledge, and ability with PHP. We’ll start with expressions and statements.

Expressions

There are several building blocks of coding that you need to understand: statements, expressions, and operators. A statement is code that performs a task. Statements are made up of expressions and operators. An expression is a piece of code that evaluates to a value. A value can be a number, a string of text, or a Boolean.

Tip

A Boolean is an expression that results in a value of either TRUE or FALSE. For example, the expression 10 > 5 (10 is greater than 5) is a Boolean expression because the result is TRUE. All expressions that contain relational operators, such as the less-than sign (<), are Boolean. Some of the Boolean operators are AND, OR, and NOT. Boolean operators will be discussed at greater length later in this chapter.

An operator is a code element that acts on an expression in some way. For instance, a minus sign (-) can be used to tell the computer to decrement the value of the expression after it from the expression before it. For example:

$account_balance=$credits-$debits;

The most important thing to understand about expressions is how to combine them into compound expressions and statements using operators. So, we’re going to look at operators used to turn expressions into more complex expressions and statements.

The simplest ...