Learning PHP, MySQL & JavaScript, 6th Edition

Chapter 4. Expressions and Control Flow in PHP

The previous chapter introduced several topics in passing that this chapter covers more fully, such as making choices (branching) and creating complex expressions. In the previous chapter, I wanted to focus on the most basic syntax and operations in PHP, but I couldn’t avoid touching on more advanced topics. Now I can fill in the background that you need to use these powerful PHP features properly.

In this chapter, you will get a thorough grounding in how PHP programming works in practice and how to control the flow of the program.

Expressions

Let’s start with the most fundamental part of any programming language: expressions.

An expression is a combination of values, variables, operators, and functions that results in a value. It’s familiar to anyone who has taken high-school algebra. Here’s an example:

y = 3 (|2x| + 4)

Which in PHP would be:

$y = 3 * (abs(2 * $x) + 4);

The value returned (y in this mathematical statement, or $y in the PHP) can be a number, a string, or a Boolean value (named after George Boole, a 19th-century English mathematician and philosopher). By now, you should be familiar with the first two value types, but I’ll explain the third.

TRUE or FALSE?

A basic Boolean value can be either TRUE or FALSE. For example, the expression 20 > 9 (20 is greater than 9) is TRUE, and the expression 5 == 6 (5 is equal to 6) is FALSE. (You can combine such operations using other classic Boolean operators such as AND, OR