Operator Precedence

The precedence of an operator specifies how "tightly" it binds two expressions together. For example, in the expression 1 + 5 * 3, the answer is 16 and not 18 because the multiplication ("*") operator has a higher precedence than the addition ("+") operator. Parentheses may be used to force precedence, if necessary. For instance: (1 + 5) * 3 evaluates to 18.

When operators have equal precedence, their associativity decides whether they are evaluated starting from the right, or starting from the left - see the examples below.

The following table lists the operators in order of precedence, with the highest-precedence ones at the top. Operators on the same line have equal precedence, in which case associativity decides the order of evaluation.

**Operator Precedence**
Associativity	Operators	Additional Information
non-associative	clone new	clone and new
left	[	array()
right	++ -- ~ (int) (float) (string) (array) (object) (bool) @	types and increment/decrement
non-associative	instanceof	types
right	!	logical
left	* / %	arithmetic
left	+ - .	arithmetic i string
left	<< >>	bitwise
non-associative	< <= > >=	comparison
non-associative	== != === !== <>	comparison
left	&	bitwise i references
left	^	bitwise
left	\|	bitwise
left	&&	logical
left	\|\|	logical
left	? :	ternary
right	= += -= *= /= .= %= &= \|= ^= <<= >>= =>	assignment
left	and	logical
left	xor	logical
left	or	logical
left	,	many uses

For operators of equal precedence, left associativity means that evaluation proceeds from left to right, and right associativity means the opposite.

Przykład #1 Associativity


<?php
$a = 3 * 3 % 5; // (3 * 3) % 5 = 4
$a = true ? 0 : true ? 1 : 2; // (true ? 0 : true) ? 1 : 2 = 2

$a = 1;
$b = 2;
$a = $b += 3; // $a = ($b += 3) -> $a = 5, $b = 5

// mixing ++ and + produces undefined behavior
$a = 1;
echo ++$a + $a++; // may print 4 or 5
?>

Use of parentheses, even when not strictly necessary, can often increase readability of the code.

Informacja:
Although = has a lower precedence than most other operators, PHP will still allow expressions similar to the following: if (!$a = foo()), in which case the return value of foo() is put into $a.