Question

Write a java program

The last digit of a credit card number is the check digit, which protects againts transaction errors. The following method is used to veryfy credit card numbers. For the simplicity we can assume that the credit card has 8 digits instead of 16. Follwing steps explains the algorithm in determining if a credit card number is a valid card.

 Starting from the right most digit, form the sum of every other digit. For example, if the credit card is number is 43589795 then you form the sum 5+7+8+3 = 23

1

•  Double each digit that we have not included in the preceding step. Add all digits of resulting numbers. For example, with the number given above, doubling the digits starting with next to last one, yields 18, 18, 10, 8. Adding all digits in these values yield 1+8+1+8+1+0+8 = 27

•  Add sum of the two preceding steps. If the last digit of the result is zero, then the number is valid number

  Write a Java program that implements this algorithm (Designing your solution and perhaps wring the algorithm in pseudocode might be helpful). Your program should ask the user 8 digit credit card number and the printout if the credit card is valid or invalid card

  Grading Criteria:

  a) The correctness of your program/solution
  b) Variable naming (self describing)
  c) Identification of proper data type and constants (if applicable) d) Appropriate commenting and Indentation.

NOTE: the given card number 43589795 should produce a valid number

Answer 1

// Java program to check if a given credit
// card is valid or not.
import java.util.Scanner;

public class CreditCard {
   // Main Method
   public static void main(String[] args)
   {
       System.out.print("Enter 8 digit credit card cardNumber :");
       int cardNumber = new Scanner(System.in).nextInt();
       String num = cardNumber + "";
      
      
       int sumOfDoubleEvenPlace = 0;
       for (int i = num.length() - 2; i >= 0; i -= 2)
           sumOfDoubleEvenPlace += getDigit(Integer.parseInt(num.charAt(i) + "") * 2);
      
       // Return sum of odd-place digits in cardNumber
       int sumOfOddPlace = 0;
       for (int i = num.length() - 1; i >= 0; i -= 2)
           sumOfOddPlace += Integer.parseInt(num.charAt(i) + "");  
      
       //Return true if the card cardNumber is valid
       boolean isValid = (sumOfDoubleEvenPlace + sumOfOddPlace) % 10 == 0;
       System.out.println(cardNumber + " is " +
       (isValid? "valid" : "invalid"));
   }

   // Return this cardNumber if it is a single digit, otherwise,
   // return the sum of the two digits
   public static int getDigit(int cardNumber)
   {
       if (cardNumber < 9)
           return cardNumber;
       return cardNumber / 10 + cardNumber % 10;
   }
}