PHP Tutorials - Herong's Tutorial Examples - v5.17, by Herong Yang
What Is an Expression
This section provides an introduction of what is an expression. A data literal or a variable is a simple expression. A single operation or a group of multiple operations is a complex express.
What Is an Expression? Giving a precise single definition of an expression is not an easy task. So I will try to define it in a recursive way:
1. A simple expression is a presentation of a data value like, a literal, a variable, an element of an array, or a function call.
2. A complex expression is a presentation of a data value returned from an operation represented by an operator, and one or two expressions as operands. The operation will result a new data value.
If you apply rule #2 recursively, an expression may contain multiple operations in a sequence. When this happens, operations must be carried out in an order defined by the following rules:
A. The operation enclosed in a pair of parentheses must be carried out before an operation outside the parentheses.
B. The operation with a higher precedence must be carried out before an operation with lower precedence.
C. The operation on the left must be carried out before the operation on the right.
D. Rule A must be applied before Rule B, which must be applied before Rule C.
Examples of expressions:
"Hello world!" # Simple expression - a String literal 777 # Simple expression - an Integer literal $author # Simple expression - a variable getdate() # Simple expression - a function call 7*9.99 # Complex expression - an arithmetic operation "Hello ".$author # Complex expression - a string concatenation (7+2)*9.99 > 50 # Complex expression - multiple operations
Table of Contents
Introduction and Installation of PHP
PHP Data Types and Data Literals
Variables, References, and Constants
►Expressions, Operations and Type Conversions
Data Type Automatic Conversion
Conditional Statements - "if" and "switch"
Loop Statements - "while", "for", and "do ... while"
Function Declaration, Arguments, and Return Values
Interface with Operating System
Introduction of Class and Object
Integrating PHP with Apache Web Server
Retrieving Information from HTTP Requests
Creating and Managing Sessions in PHP Scripts
Sending and Receiving Cookies in PHP Scripts
Controlling HTTP Response Header Lines in PHP Scripts
MySQL Server Connection and Access Functions
Functions to Manage Directories, Files and Images
SOAP Extension Function and Calling Web Services
SOAP Server Functions and Examples
Localization Overview of Web Applications
Using Non-ASCII Characters in HTML Documents
Using Non-ASCII Characters as PHP Script String Literals
Receiving Non-ASCII Characters from Input Forms
"mbstring" Extension and Non-ASCII Encoding Management
Managing Non-ASCII Character Strings with MySQL Servers
Parsing and Managing HTML Documents
Configuring and Sending Out Emails
Managing PHP Engine and Modules on macOS