What is the precedence of php operators?

PHP operator priority

PHP operator priority describes the order in which operations are performed when the computer calculates expressions. . Operations with higher priority are performed first, followed by operations with lower priority. For example, we often say that multiplication and division are performed first, and then addition and subtraction are performed.

Order of php operator precedence

The following table lists the precedence of operators from high to low. Operators in the same line have the same precedence, and the precedence of operators is evaluated from left to right in the expression.

Priority	Combining direction	Operator	Additional information
1	non-binding	clone new	clone and new
2	left	[	array()
3	Non-associative	--	Increment/decrement operator
4	Non-associative	~-(int)(float)(string)(array)(object)(bool)@	Type
5	Non-associative	instanceof	Type
6	Right combination	!	Logical operator
7	Left	*/ %	Arithmetic operator
8	left	-.	Arithmetic operators and string operators
9	left	<<&gt ;>	Bitwise operators
10	Non-associative	<<= >>=<>	Comparison operator
11	Non-associative	==!====!==	Comparison operator
12	left	&	Bitwise Operators and References
13	left	^	Bitwise operators
14	left	|	Bitwise operations Symbol
15	left	&&	Logical operator
16	left	||	Logical operator
17	left	?:	ternary operator
18	right	= =-=*=/= .= %= &= |= ^= <<= >>=	Assignment Operator
19	left	and	logical operator
20	left	xor	logical operator
21	left	or	logical operator
22	left	,

is used in many places to illustrate that

pairs have the same For precedence operators, the left associative direction means that the evaluation will be from left to right, and the right associative direction means the opposite. It is possible that an operator with the same precedence without associative direction cannot be combined with itself.

For example, in PHP 1 < 2 > 1 is an illegal statement, but 1 <= 1 == 1 is not. Because <= has higher priority than ==.

<?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
?>

So under the premise that we are very clear about the priority of PHP operations, it is best to use parentheses to mark the priority when writing operators. This is more readable and is also a good programming Habit.

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