What does operator precedence look like in php?

Operator precedenceSpecifies how "tightly" two expressions are bound. For example, the expression 1 + 5 * 3 evaluates to 16 instead of 18 because the multiplication sign ("*") has higher precedence than the plus sign ("+"). Parentheses can be used to force a priority change if necessary. For example: (1 + 5) * 3 has the value 18.

If operators have the same precedence, their combination direction determines whether evaluation should be from right to left or from left to right - see the example below.

The following table lists the operators from high to low precedence. Operators in the same line have the same precedence, and the direction in which they are combined determines the order of evaluation.

The operator priority is as follows

##Noneclone new clone and newleft[ Right++ -- ~ (int) (float) (string) (array) (object) (bool) @type and increment/decrementNoneinstanceofTypeRight!left* / %left+ - .arithmetic operators and left10e3fdaca48eb0367c6d60dbc98f885d>Bitwise operatorsNone== != === !== 6d267e5fab17ea8bc578f9e7e5e1570bComparison operators##leftleftleftleftleft##left? :Ternary operatorright= += -= *= /= .= %= &= |= ^= 639513f5eb9d8dcbce09d6b5cb44cf73>= =>leftandlogical operatorleftxorlogical operatorleftorlogical operatorleft, is used in many places For operators with the same priority, the left combination direction This means that the evaluation will be from left to right, and vice versa for right combination directions. It is possible that an operator with the same precedence without associative direction cannot be combined with itself. For example, in PHP 1 d66d2a93259ca9392db29f00ed43fda0 1 is an illegal statement, but 1 <= 1 == 1 is not. Because the priority of the T_IS_EQUAL operator

Operator priority

Combined Direction	Operator	Additional information
		array()
		Logical operation Symbol
		Arithmetic operator
		string operators
&	Bitwise operators and references
^	bit operator
|	bit operator
&&	logical operator
||	Logical operator
	Assignment operator

is lower than that of the T_IS_SMALLER_OR_EQUAL operator.

Example #1 In conjunction with direction

<?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
?>

Using parentheses can often enhance the readability of your code, even when they are not strictly needed.

Note:

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

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