Learning PHP, MySQL, JavaScript, and CSS, 2nd Edition

Operators

PHP offers a lot of powerful operators, ranging from arithmetic, string, and logical operators to operators for assignment, comparison, and more (see Table 4-1).

Table 4-1. PHP operator types

Operator	Used for	Example
Arithmetic	Basic mathematics	$a + $b
Array	Array union	$a + $b
Assignment	Assigning values	$a = $b + 23
Bitwise	Manipulating bits within bytes	12 ^ 9
Comparison	Comparing two values	$a < $b
Execution	Executing contents of backticks	`ls -al`
Increment/Decrement	Adding or subtracting 1	$a++
Logical	Boolean comparisons	$a and $b
String	Concatenation	$a . $b

Different types of operators take a different number of operands:

• Unary operators, such as incrementing ($a++) or negation (-$a), take a single operand.

• Binary operators, which represent the bulk of PHP operators (including addition, subtraction, multiplication, and division), take two operands.

• There is one ternary operator, which takes the form x ? y : z. It’s a terse, single-line if statement that chooses between two expressions, depending on the result of a third one. This conditional operator takes three operands.

Operator Precedence

If all operators had the same precedence, they would be processed in the order in which they are encountered. In fact, many operators do have the same precedence—Example 4-5 illustrates one such case.

Example 4-5. Three equivalent expressions

1 + 2 + 3 - 4 + 5
2 - 4 + 5 + 3 + 1
5 + 2 - 4 + 1 + 3

Here you will see that although the numbers (and their preceding operators) have been moved around, ...