Natour, O. 10/25/15 Csc-111-D01 Hw 5.47

/*
 * Name: Omar Natour
 * Date: 10/26/15
 * Course Number: CSC-111
 * Course Name: Introduction to Java Programming
 * Problem Number: 5.47
 * Email: ojnatour0001@student.stcc.edu
 * Problem Description: Use the first 12 digits of the isbn number to find the 13th.
 */

import java.util.Scanner;

public class HomeWork6 {

    public static void main(String args[]) {
        final String TITLE = "The ISBN-13 calculator";
        final String CONTINUE_PROMPT = "Do this again? [y/N] ";

        System.out.println("Welcome to " + TITLE);
        Scanner sc = new Scanner(System.in);
        do {

            System.out.print("Enter the first 12 digits of an ISBN-13 as a string:");
            System.out.println(calc(sc.nextLine()));

        } while (doThisAgain(sc, CONTINUE_PROMPT));

        sc.close();

        System.out.println();
        System.out.println("Thank you for using " + TITLE);
    }

    // ************************************************************************

    private static boolean doThisAgain(Scanner sc, String prompt) {
        System.out.print(prompt);
        String doOver = sc.nextLine();
        return doOver.equalsIgnoreCase("Y");
    }

    // ************************************************************************

    private static String calc(String twelve) {
        int sum = 0;
        String out = "";

        if (twelve.length() != 12)
            return twelve + " is an invalid input.";
        else {
            for (int i = 0; i < twelve.length(); i++) {
                int asci = twelve.charAt(i);

                if (!(asci >= 48 && asci <= 57))
                    return twelve + " is an invalid input.";
                else {

                    int dig = -48 + asci;
                    out += dig;

                    if (i % 2 == 0)
                        sum += dig;
                    else
                        sum += (3 * dig);
                }
            }
        }
        int back = 10 - sum % 10;

        if (back == 10)
            return "the ISBN-13 number is " + out + 0 + ".";
        else
            return "the ISBN-13 number is " + out + back + ".";
    }
}