PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Understanding Precedence and Associativity
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Table 1.7 Operator Precedence in PHP
Associativity Operators
left ,
left
or
left
xor
left
and
right
print
left = += -= *= /= .= %= &= |= ^= ~= =
left ? :
left ||
left
&&
left |
left
^
left
&
n/a == != === !==
n/a < >=
left >
left + - .
left * / %
right
! ~ ++ -- (int) (double) (string) (array) (object) @
right []
n/a
new
n/a ()
Notice that we haven’t yet covered the operator with the highest precedence: plain old
parentheses.The effect of using parentheses is to raise the precedence of whatever is contained
within them.This is how you can deliberately manipulate or work around the
precedence rules when you need to.
Remember this part of the preceding example:
$totalamount = $totalamount * (1 + $taxrate);
If you had written
$totalamount = $totalamount * 1 + $taxrate;
the multiplication operation, having higher precedence than the addition operation,
would be performed first, giving an incorrect result. By using the parentheses, you can
force the subexpression 1 + $taxrate to be evaluated first.
You can use as many sets of parentheses as you like in an expression.The innermost
set of parentheses is evaluated first.
Also note one other operator in this table we have not yet covered: the print language
construct, which is equivalent to echo. Both constructs generate output.