How do you use veto?

Answer 1

num$=""

error=FALSE

PRINT " Enter ISBN number"

INPUT num$

IF LEN (num$)<>10 THEN error=TRUE

FOR pos%=1 TO 10

character$=MID$(num$, pos%,1)

IF ASC(character$)<48 OR ASC(character$)>57 THEN error=TRUE

NEXT

IF error= FALSE THEN

multiplier%=11

FOR pos%=1 TO 10