Check Your Digits

Program parses the number entered and either returns the ISBN check digit or the checksum for the number provided, why or why not it is valid, and how many digits you passed in. If a 9 digit number is entered, the program will compute the check digit for ISBN-10. If 10 digits are entered, it will return whether or not the number is a valid ISBN-10 number. If 12 digits are entered, it will return the check digit for ISBN-13. If 13 numbers are entered, it will return whethre or not the number is a valid ISBN-13 number.