7 Subprograms

Multiple-Line Function Subprograms

DEF FN subprogram name [(formal parameter list)]

For a string function, the first line is:

DEF FN subprogram name$ [(formal parameter list)]

The subprogram name must be a valid name.

The last line in a multiple-line function subprogram should be:

FNEND

The value to be returned to the calling program segment as the value of the function is specified by:

RETURN numeric expression

or

RETURN string expression

The function subprogram is called automatically by specifying the function name and pass parameter list in a program line:

FN subprogram name [(pass parameter list)]

or

FN subprogram name$ [(pass parameter list)]

Here is an example of a numeric function:

10   DIM C(50)
20   A=10
30   B=20
40   FOR I=0 TO 50
50     C(I)=I
60   NEXT I
70   X=FNTotal(A,B,C(*))
80   PRINT "RESULT=";X
 .
 .
120  END
130  DEF FNTotal(X,Y,Z(*))
140     Tot=0
150     FOR I=X TO Y
160       Tot=Tot+Z(I)
170     NEXT I
180     RETURN Tot
190     FNEND

RUN
RESULT= 165

Notice that the variable X in the function subprogram is not the same as X in the main program.

Here is an example of a string function:

10   A$="HELLO"
20   B$="GOODBYE"
30   Rep=2
40   PRINT FNResult$(A$,B$)
50   END
60   DEF FNResult$(H$,G$)
70      String$=H$"..."G$
80      RETURN "****"TRIM$(String$)"****"
90      FNEND

RUN
****HELLO...GOODBYE****

10   DIM C(2,2)
20   C(0,0)=C(0,1)=C(1,0)=C(1,1)=2
30   A=B=4
40   PRINT "RESULT=";FNTotals(A,B,C(*))
50   END
60   DEF FNTotals(X,Y,Z(*))
70     A=Z(0,0)+Z(0,1)+Z(1,0)+Z(1,1)
80     B=X+Y+A
90     IF XY THEN RETURN B
100    RETURN 2*B
110    FNEND

RUN
RESULT= 32