Operators
Please note that certain operators change the variable type in ways you may not expect.
If you want to append the result of an arithmetic operation to a string you have to do it in two steps:
<?php
$ord = $i + 1;
$field = "cellID" . $ord; // returns a string
$field = "cellID" . $i + 1; // because of the addition it returns an int
?>
Operator Precedence
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. If operator precedence is equal, left to right associativity is used.
The following table lists the precedence of operators with the highest-precedence operators listed at the top of the table. Operators on the same line have equal precedence, in which case their associativity decides which order to evaluate them in.
| 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 |
Left associativity means that the expression is evaluated from left to right, 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, $b = 5
?>
Use parentheses to increase readability of the code.
Note: Although = has a lower precedence than most other operators, PHP will still allow expressions similar to the following: if (!$a = foo()), in which case the return value of foo() is put into $a.
add a note
User Contributed NotesOperator Precedence
Patryk Bratkowski
07-Oct-2009 02:18
07-Oct-2009 02:18
headden at karelia dot ru
09-Jun-2009 11:02
09-Jun-2009 11:02
Although example above already shows it, I'd like to explicitly state that ?: associativity DIFFERS from that of C++. I.e. convenient switch/case-like expressions of the form
$i==1 ? "one" :
$i==2 ? "two" :
$i==3 ? "three" :
"error";
will not work in PHP as expected
Pies
08-Feb-2009 07:22
08-Feb-2009 07:22
You can use the "or" and "and" keywords' lower precedence for a bit of syntax candy:
<?php
$page = (int) @$_GET['page'] or $page = 1;
?>