Using the negation operator

 
<?
$finished = false;

if ($finished == false) {
    print 'Not done yet!';
}

if (! $finished) {
    print 'Not done yet!';
}
?>

1.	Arithmetic Operators
2.	Arithmetical Operators
3.	An example of PHP's automatic type conversion is the addition operator '+'.
4.	Changing the default precedence using parentheses
5.	Increment/decrement Operators
6.	Incrementing and decrementing
7.	Using the autodecrement operator
8.	Using pre- and postincrement
9.	Using autoincrement to add to a variable
10.	Postfix and Prefix Operators summary table
11.	Peculiarities of the ++ and -- Operators
12.	postfix and prefix increment operators also work on letter values
13.	Postfix and Prefix Operators in Action
14.	Calculation Results for Postfix and Prefix Operators
15.	Shorthand Operators summary table
16.	Variables Are Assigned by Value
17.	Using Assignment Operators

Using the negation operator : Arithmetic Operators « Operator « PHP