Lecture Notes on 4 Feb 2013

import java.util.*;

public class CreditCard
{
  public static void main (String[] args)
  {
    // Prompt the user to enter a 16-digit number and read input
    Scanner sc = new Scanner (System.in);

    System.out.print ("Enter 16-digit credit card number: ");

    long ccNum = sc.nextLong();
    long ccNum_orig = ccNum;


    // Check input if 16-digit number
    if ((ccNum < 1000000000000000L) || (ccNum > 9999999999999999L))
    {
      // Write an error message

      return;
    }

    // Get individual digits of credit card
    int d16 = (int)(ccNum % 10);

    ccNum = ccNum / 10;
    int d15 = (int)(ccNum % 10);

    ....

    // Apply Luhn's test

    d15 = d15 * 2;
    d15 = (d15 % 10) + (d15 / 10);

    ....

    int sumDigits = ....;

    // Write the validity of the credit card number

    if (sumDigits % 10 == 0)
    {

    }
    else
    {

    }
  }
}