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.
Operator Precedence 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
$a = 5, $b = 5
// mixing ++ and + produces undefined behavior
$a = 1;
echo ++$a + $a++; // may print 4 or 5
Use parentheses to increase readability of the code.