false -- a constant with the value of 0
The constant false can be assigned to variables which later appear in conditions (e.g. within an if-statement.
false may also be written as FALSE or even FaLsE.
input "Please enter a number between 1 and 10: " a
if (check_input(a)) print "Okay"
if (x>10 or x<1) return false
The subroutine check_input checks its argument and returns true or false according to the outcome of the check.