optional Example
10 CLEAR SCREEN
20 PRINT "5 + 8 =";FNAdd(5,8)
30 PRINT FNMessage$
40 PRINT FNMessage$("Hello")
50 END
60 DEF FNAdd(A,B)
70 RETURN A+B
80 FNEND
90 DEF FNMessage$(OPTIONAL String$)
100 IF NPAR=0 THEN RETURN "OPTIONAL parameter not used."
110 RETURN "OPTIONAL parameter used."
120 FNEND
