Question

Please fix my code so I can get this output: Enter the first 12-digit of an ISBN number as a string: 978013213080 The ISBN number is 9780132130806
This was my output: 

import java.util.Scanner;

public class Isbn {

    private static int getChecksum(String s) {
        // Calculate checksum
        int sum = 0;
        for (int i = 0; i < s.length(); i++)
            if (i % 2 == 0)
                sum +=  (s.charAt(i) - '0') * 3;
            else
                sum  += s.charAt(i) - '0';

        return 10 - sum;
    }

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter the first 12-digit of an ISBN number as a string: ");
        // get a string input
        String s = input.nextLine();

        if (s.length()!= 12) {
            System.out.println(s + " is an invalid input");
            System.exit(1);
        }

        int checksum = getChecksum(s);
        System.out.println("The ISBN number is " + s +
                (checksum == 10 ? "0" : checksum));
    }
}
/*Enter the first 12-digit of an ISBN number as a string: 97801320
97801320 is an invalid input*/

Answer 1

import java.util.Scanner;

public class Exercise {
public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    System.out.print("Enter the first 12-digit of an ISBN number as a string: ");
    String s = input.nextLine();

    if (s.length() != 12) {
      System.out.println(s + " is an invalid input");
      System.exit(1);
    }

    // Calculate checksum
    int sum = 0;
    for (int i = 0; i < s.length(); i++)
      if (i % 2 == 0)
        sum += (s.charAt(i) - '0');
      else
        sum += (s.charAt(i) - '0') * 3;

    int checksum = 10 - sum % 10;

    System.out.println("The ISBN number is " + s +
        (checksum == 10 ? "0" : checksum));
}
}