Bronze Edition Guide - True BASIC

166 BRONZE Edition Guide
SUB Structure
SUB identifier (parm 1, ... , param n)
...
EXIT SUB [optional]
...
END SUB
The subroutine may contain one or more EXITSUB statements. A CALLstatement
invokes the subroutine; that is, starts it running. The arguments in the CALL must
match the parameter in the SUB statement in number, position, type, and number of
dimensions. Parameter passing is by reference; that is, changes to the parameter within
the subroutine will cause simultaneous changes to the arguments in the CALL statement.
WHEN Structure
WHEN EXCEPTION IN
... ! Protected part
USE
... ! Executed if an exception is in a protected part
END WHEN
This subroutine may be used to “trap” run-time errors called exceptions. Examples might
be division by 0 or attempting to open a file that doesn’t exist.
If an exception of any type occurs in the protected portion, the recovery statements between
the USE statement and the END WHEN statement are executed. If no exception occurs in
the protected part, the recovery statements are ignored.
The functions EXLINE, EXLINE$, EXTEXT$, and EXTYPE can be used to determine the
exact nature of an exception.