PHP

declare boolean php

<?php
$foo = True; // assign the value TRUE to $foo
?>

php boolean

Booleans can be one of two constants:
true
false
These values are not case sensitive, therefore true is the same as TRUE

booleans are also often used in control structures, either directly or as
a result of an operation. For example:

if ($waterDrankToday > 3.7) {
 echo "Good work staying hydrated!";
 if ($havingABadDay)
   hug();
}
else
  echo "You should drink more water";