Programming PHP, 4th Edition

Chapter 2. Language Basics

This chapter provides a whirlwind tour of the core PHP language, covering such basic topics as data types, variables, operators, and flow-control statements. PHP is strongly influenced by other programming languages, such as Perl and C, so if you’ve had experience with those languages, PHP should be easy to pick up. If PHP is one of your first programming languages, don’t panic. We start with the basic units of a PHP program and build up your knowledge from there.

Lexical Structure

The lexical structure of a programming language is the set of basic rules that governs how you write programs in that language. It is the lowest-level syntax of the language and specifies such things as what variable names look like, what characters are used for comments, and how program statements are separated from each other.

Case Sensitivity

The names of user-defined classes and functions, as well as built-in constructs and keywords (such as echo, while, class, etc.), are case-insensitive. Thus, these three lines are equivalent:

echo("hello, world");
ECHO("hello, world");
EcHo("hello, world");

Variables, on the other hand, are case-sensitive. That is, $name, $NAME, and $NaME are three different variables.

Statements and Semicolons

A statement is a collection of PHP code that does something. It can be as simple as a variable assignment or as complicated as a loop with multiple exit points. Here is a small sample of PHP statements, including function calls, some variable ...