Operator precedence
The precedence of operators in an expression is similar to the precedence defined in any other language. Multiplication and division occur before subtraction and addition, and so on. However, reliance on evaluation order leads to unreadable, confusing code. Rather than memorize the rules, we recommend you construct unambiguous expressions with parentheses, because parentheses have the highest precedence in evaluation.
For example, in the following fragment $variable is assigned a value of 32 because of the precedence of multiplication over addition:
$variable = 2 + 5 * 6;
The result is much clearer if parentheses are used:
$variable = 2 + (5 * 6);