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.

Associativity | Operators | Additional Information |
---|---|---|

non-associative | clone new | clone and new |

left | [ | array() |

non-associative | ++ -- | increment/decrement |

right | ~ - (int) (float) (string) (array) (object) (bool) @ | types |

non-associative | instanceof | types |

right | ! | logical |

left | * / % | arithmetic |

left | + - . | arithmetic and string |

left | << >> | bitwise |

non-associative | < <= > >= <> | comparison |

non-associative | == != === !== | comparison |

left | & | bitwise and 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.

**Example #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

?>

Note:Although

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