Operator Precedence in PHP

PHP Operators – Part 7

Forward: In this part of the series we look at operator precedence in PHP.

By: Chrysanthus Date Published: 10 Aug 2012

Introduction

This is part 7 of my series, PHP Operators. It is possible to have a statement with many operators. The question is, which operator is executed first? Some operators will always be executed first before others. In fact there are different levels of this, and that is operator precedence. In this part of the series we look at operator precedence in PHP.

Note: If you cannot see the code or if you think anything is missing (broken link, image absent), just contact me at forchatrans@yahoo.com. That is, contact me for the slightest problem you have about what you are reading.

Example
Consider the following statement:

$x = 2 + 5 * 3;

There are three operators here, which are =, + and *. Now = is of a very low precedence and it is executed last. The question then is between + and -; which is executed first? If the multiplication operator, * is executed first, the answer will be 17. If the addition operator is executed first, the answer will be 21. Well, in PHP, * is of a higher precedence than +, so * is executed first and the answer is 21. You can force the + to be executed first by using brackets, as follows:

int x = (2 + 8) * 5;

Whenever you are in doubts of which operator would be executed first, use brackets, to be sure that an operator would be executed first. Brackets can be nested.

Associativity means operation from left to right or operation from right to left. Left associativity means that the operation of the operator is from left to right. Right associativity means the operation is from right to left. This has been indicated in the previous parts of the series, but the word, associativity was not mentioned. In the absence of brackets, if a series of operators (with their operands) are of the same level, then associativity is used in the series of operations.

Still on associativity, consider the following expression:

9-4-2

Subtraction is left associative, so the 9-4 is done first to give 5-2 = 3 instead of 4-2 first, to result in 9-2 = 7.

Precedence Order

I now give you the precedence order for the operators we have seen. This list has majority of PHP operators. The highest precedence is given first, that is followed by the second, then third, and so on, until the last.

Increment/Decrement Operators
++ --
Associativity: Non-associative

Not Operator
!
Associativity: Right-to-Left

Array Operator
[
Associativity: Left-to-Right

Multiplicative Operators
% * /
Associativity: Left-to-right

Additive and String Operators
+ - .
Associativity: Left-to-right

Comparison Operators
< <= > >= <>
Associativity: Non-associative

Equality and Identity Operators
== != === !==
Associativity: Non-associative

Reference Operator
&
Associativity: Left-to-right

Logical AND Operator
&&
Associativity: Left-to-right

Ternary Operator
? :
Associativity: Left-to-right

Assignment Operators
= += -= *= /= .= %=
Associativity: Right-to-Left

Logical WORD AND Operator
and
Associativity: Left-to-right

Logical Exclusive Or Operator
xor
Associativity: Left-to-right

Logical or Operator
or
Associativity: Left-to-right

Comma Operator
,
Associativity: Left-to-right

Well, we have seen a lot in this series. We should really take a break here. We continue in the next part.

Chrys

Broad Network

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Operator Precedence in PHP

PHP Operators – Part 7

Introduction

Precedence Order

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