php - Booleans

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.

Syntax

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

<?php
$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.

<?php
// == is an operator which test
// equality and returns a boolean
if ($action == "show_version") {
  echo "The version is 1.23";
}
// this is not necessary...
if ($show_separators == TRUE) {
  echo "<hr>\n";
}
// ...because you can simply type 
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:

• the boolean FALSE itself
• the integer 0 (zero)
• the float 0.0 (zero)
• the empty string, and the string "0"
• an array with zero elements
• an object with zero member variables (PHP 4 only)
• the special type NULL (including unset variables)
• SimpleXML objects created from empty tags

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

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

<?php
var_dump((bool) ""); // bool(false) 
var_dump((bool) 1); // bool(true) 
var_dump((bool) -2); // bool(true) 
var_dump((bool) "foo"); // bool(true) 
var_dump((bool) 2.3e5); // bool(true) 
var_dump((bool) array(12)); // bool(true) 
var_dump((bool) array()); // bool(false) 
var_dump((bool) "false"); // bool(true)
?>