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Chapter 14. Statement Reference

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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 definition block,

they will be treated as local variables whose current values are available 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 realparameters should be equal to that of dummyparameters, 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 realparameters are passed not by address but by value.

(So called "Call-by-value")

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