Precedence Order of PHP operators

The operator precedence specifies how tightly the two expressions are bound. For example, the result of an expression 1 + 5 * 3 is 16 instead of 18 because multiplication sign ("*") has a higher precedence than a plus sign ("+"). You can use parentheses to force a change of precedence if necessary. For example: (1 + 5) * 3 has a value of 18.

If the operator has the same precedence, its binding direction determines whether the value should be evaluated from right to left or left to right-see the following example.

The following table lists the operators by priority from high to low. Operators in the same row have the same precedence, at which point their binding direction determines the order of evaluation.

Combination Direction	operator	Additional Information
No	Clone new	Clone and New
Left	[	Array ()
Right	++-~ (int) (float) (string) (array) (object) (BOOL) @	Type and increment/decrement
No	instanceof	Type
Right	!	logical operators
Left	* / %	Arithmetic operators
Left	+–.	Arithmetic operators and string operators
Left	<< >>	Bitwise operators
No	= = = = = = =!== <>	Comparison operators
Left	&	Bitwise operators and references
Left	^	Bitwise operators
Left	|	Bitwise operators
Left	&&	logical operators
Left	||	logical operators
Left	? :	Ternary operators
Right	= + = = *=/=. =%= &= |= ^= <<= >>= =	Assignment operators
Left	and	logical operators
Left	Xor	logical operators
Left	Or	logical operators
Left	,	Used in many places

For operators with the same precedence, the left-associative direction means that the left-to-right value is evaluated and the right-bound direction is the opposite. For operators with the same precedence in a no-union direction, the operator may not be able to combine with itself. For example, in PHP 1 < 2 > 1 is an illegal statement, and 1 <= 1 = = 1 is not. Because the t_is_equal operator has a lower precedence than the t_is_smaller_or_equal operator.

Example with direction, the code is as follows

<?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 + + produces undefined behavior $a = 1; echo + + $a + $a + +; May print 4 or 5?>

PS: Using parentheses, you can usually enhance the readability of your code even when it is not strictly needed.

Although = is lower than most other operators, PHP still allows an expression similar to the following: if (! $a = foo ()), in this case the return value of foo () is assigned to the $a.