This is the easiest type. A boolean expresses a truth value. It can be either TRUE or FALSE.

Note: The boolean type was introduced in PHP 4.


To specify a boolean literal, use either the keyword TRUE or FALSE. Both are case-insensitive.

$foo = True; // assign the value TRUE to $foo     

Usually you use some kind of operator which returns a boolean value, and then pass it on to a control structure.

if ($action == "show_version") { // == is an operator which returns a boolean
    echo "The version is 1.23";

// this is not necessary:
if ($show_separators == true) {
    echo "<hr>\n";

// because you can simply type this:
if ($show_separators) {
    echo "<hr>\n";

Converting to boolean

To explicitly convert a value to boolean, use either the (bool) or the (boolean) cast. However, in most cases you do not need to use the cast, since a value will be automatically converted if an operator, function or control structure requires a boolean argument.

See also Type Juggling.

When converting to boolean, the following values are considered FALSE:

Every other value is considered TRUE (including any resource).


-1 is considered TRUE, like any other non-zero (whether negative or positive) number!