Programs / Predefined constants |
The NULL constant is provided as the "nil" value.
NULL
When comparing variables to NULL, use the IS NULL operator, not the equal operator.
If an element of an expression is null, the expression is evaluated to NULL.
Variables are initialized to NULL or to zero, according to their data type.
Empty character string literals ("") are equivalent to NULL.
NULL cannot be used with the = equal comparison operation, you must use IS NULL.
MAIN DEFINE s CHAR(5) LET s = NULL DISPLAY "s IS NULL evaluates to:" IF s IS NULL THEN DISPLAY "TRUE" ELSE DISPLAY "FALSE" END IF END MAIN