Programming PHP, 3rd Edition

Expressions and Operators

An expression is a bit of PHP that can be evaluated to produce a value. The simplest expressions are literal values and variables. A literal value evaluates to itself, while a variable evaluates to the value stored in the variable. More complex expressions can be formed using simple expressions and operators.

An operator takes some values (the operands) and does something (for instance, adds them together). Operators are written as punctuation symbols—for instance, the + and – familiar to us from math. Some operators modify their operands, while most do not.

Table 2-3 summarizes the operators in PHP, many of which were borrowed from C and Perl. The column labeled “P” gives the operator’s precedence; the operators are listed in precedence order, from highest to lowest. The column labeled “A” gives the operator’s associativity, which can be L (left-to-right), R (right-to-left), or N (nonassociative).

Table 2-3. PHP operators

P	A	Operator	Operation
21	N	clone, new	Create new object
20	L	[	Array subscript
19	R	~	Bitwise NOT
	R	++	Increment
	R	−−	Decrement
	R	(int), (bool), (float), (string), (array), (object), (unset)	Cast
	R	@	Inhibit errors
18	N	instanceof	Type testing
17	R	!	Logical NOT
16	L	*	Multiplication
	L	/	Division
	L	%	Modulus
15	L	+	Addition
	L	−	Subtraction
	L	.	String concatenation
14	L	<<	Bitwise shift left
	L	>>	Bitwise shift right
13	N	<, <=	Less than, less than or equal
	N	>, >=	Greater than, greater than or equal
12	N	==	Value equality
	N	!=, <>	Inequality
	N	===	Type and value equality
	N	!==	Type and value inequality
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