Denso BHT-BASIC 100 SERIES, Programmer'S Manual

Page: 330 / 577

Chapter 14. Statement Reference
322
Description:
■
Creating a user-defined function
SUB ... END SUB creates a user-defined function. The function definition block
between SUB and END SUB is a set of some statements and functions.
• You cannot make double definition to a same function name.
• This statement block should not be defined in the block-structured statements
( DEF FN
...
END DEF , FOR
...
NEXT , FUNCTION
...
END FUNCTION , IF
...
THEN
...
ELSE
...
END IF , SELECT
...
CASE
...
END SELECT , SUB
...
END SUB , and
WHILE
...
WEND
), in the error-handling routine, event-handling routine, or in the
subroutines.
• SUB ... END SUB functions can be recursive.
• dummyparameter , which corresponds to the variable having the same name in
the function definition block, is a local variable valid only in that block. Therefore,
if a variable having the same name as dummyparameter is used outside
SUB
...
END SUB
statement block or used as a
dummyparameter
of any other
function in the same program, then it will be independently treated.
• In user-defined functions, you can call other user-defined functions. You can nest
SUB ... END SUB statements to a maximum of 10 levels.
• When using the SUB ... END SUB together with block-structured statements ( DEF
FN
...
END DEF , FOR
...
NEXT , FUNCTION
...
END FUNCTION , IF
...
THEN
...
ELSE
...
END IF
,
SELECT
...
CASE
...
END SELECT
,
SUB
...
END SUB
, and
WHILE
...
WEND ), you can nest them to a maximum of 30 levels.
• If variables other than
dummyparameter
(s) are specified in the function defini-
tion block, they will be treated as local variables whose current values are avail-
able only in that function definition block, unless PRIVATE or GLOBAL statement
is used.
•
EXIT SUB
exits the function block prematurely and returns control to the position
immediately after the statement that called the user-defined function.
• Unlike other user-defined functions, SUB function cannot assign a return value.
■
Calling a user-defined function
CALL statement and subname call a user-defined function. CALL can be omitted.
• The number of realparameter s should be equal to that of dummyparame-
ter s, and the types of the corresponding variables used in those parameters
should be identical.
• If you specify a global variable in realparameter when calling a user-defined
function, the user-defined function cannot update the value of the global variable.
This is because all realparameter s are passed not by address but by value.
(So called "Call-by-value")