Credit Card Number Check. The last digit of a credit card number is the check di

Question

Credit Card Number Check. The last digit of a credit card number is the check digit, which protects against transcription errors such as an error in a single digit or switching two digits. The following method is used to verify actual credit card numbers but, for simplicity, we will describe it for numbers with 8 digits instead of 16: Starting from the rightmost digit, form the sum of every other digit. For example, if the credit card number is 4358 9795, then you form the sum 5 + 7 + 8 + 3 = 23 Double each of the digits that were not included in the preceding step. Add all digits of the resulting numbers. For example, with the number given above, doubling the digits, starting with the next-to-last one, yields 18 18 10 8. Adding all digits in these values yields 1 + 8 + 1 + 8 + 1 + 0 + 8 = 27 Add the sums of the two preceding steps. If the last digit of the result is 0, the number is valid. In our case, 23 + 27 = 50, so the number is valid Write a program that implements this algorithm. The user should supply an 8-digit number, and you should print out whether the number is valid or not. If it is not valid, you should print the value of the check digit that would make it valid.

Explanation / Answer

Below is your code in Java. Let me know if you have any issues: -

import java.util.Scanner;

public class CardValidator {

public static void main(String[] args) {

Scanner input = new Scanner(System.in);

System.out.print("8-digit credit card number: ");

int credit_card_number = input.nextInt();

input.close();

int remaining = getReminder(credit_card_number);

if (remaining == 0) {

System.out.println("Card number is valid");

} else {

System.out.println("Card number is invaid");

int digit_7 = credit_card_number % 10;

int check_digit = 0;

if (digit_7 - remaining < 0) {

check_digit = digit_7 + (10 - remaining);

} else {

check_digit = digit_7 - remaining;

}

System.out.println("Check digit should be: " + check_digit);

String cardNum = new Integer(credit_card_number).toString();

cardNum = cardNum.substring(0, cardNum.length() - 1);

cardNum = cardNum + check_digit;

System.out.println("New card number: " + cardNum);

int remainingNew = getReminder(Integer.parseInt(cardNum));

System.out.println("Is new card number valid : "+ (remainingNew == 0));

}

}

public static int getReminder(int credit_card_number) {

int digit_7 = credit_card_number % 10;

credit_card_number /= 10;

int digit_6 = credit_card_number % 10;

credit_card_number /= 10;

int digit_5 = credit_card_number % 10;

credit_card_number /= 10;

int digit_4 = credit_card_number % 10;

credit_card_number /= 10;

int digit_3 = credit_card_number % 10;

credit_card_number /= 10;

int digit_2 = credit_card_number % 10;

credit_card_number /= 10;

int digit_1 = credit_card_number % 10;

credit_card_number /= 10;

int digit_0 = credit_card_number % 10;

int part1 = digit_7 + digit_5 + digit_3 + digit_1;

// part 2

int twice = 2 * digit_6;

int part2 = 0;

part2 = part2 + ((twice % 10) + (twice / 10));

twice = 2 * digit_4;

part2 = part2 + ((twice % 10) + (twice / 10));

twice = 2 * digit_2;

part2 = part2 + ((twice % 10) + (twice / 10));

twice = 2 * digit_0;

part2 = part2 + ((twice % 10) + (twice / 10));

int total = part1 + part2;

int remaining = total % 10;

return remaining;

}

}

Sample Run : -

8-digit credit card number: 32323232
Card number is invaid
Check digit should be: 0
New card number: 32323230
Is new card number valid : true

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.