Java Project Credit card numbers follow certain patterns. A credit card number m
ID: 3905722 • Letter: J
Question
Java Project
Credit card numbers follow certain patterns. A credit card number must have between 13 and 16 digits. It must start with:
4 for Visa cards
5 for Master cards
37 for American Express cards
6 for Discover cards
In 1954, Hans Luhn of IBM proposed an algorithm for validating credit card numbers. The algorithm is useful to determine if a card number is entered correctly or if a credit card is scanned correctly by a scanner. Almost all credit card numbers are generated following this validity check, commonly known as the Luhn check or the Mod 10 check, which can be described as follows (for illustration, consider the card number 4388576018402626):
1. Double every second digit from right to left. If doubling of a digit results in a two-digit number, add up the two digits to get a single-digit number.
2 * 2 = 4
2 * 2 = 4
4 * 2 = 8
1 * 2 = 2
6 * 2 = 12 (1 + 2 = 3)
5 * 2 = 10 (1 + 0 = 1)
8 * 2 = 16 (1 + 6 = 7)
4 * 2 = 8
2. Now add all single-digit numbers from Step 1.
4 + 4 + 8 + 2 + 3 + 1 + 7 + 8 = 37
3. Add all digits in the odd places from right to left in the card number.
6 + 6 + 0 + 8 + 0 + 7 + 8 + 3 = 38
4. Sum the results from Step 2 and Step 3.
37 + 38 = 75
5. If the result from Step 4 is divisible by 10, the card number is valid; otherwise, it is invalid. For example, the number 4388576018402626 is invalid, but the number 4388576018410707 is valid.
Write a program that prompts the user to enter a credit card number as a long integer. Display whether the number is valid or invalid.
Here are sample runs of the program:
Sample 1:
Enter a credit card number as a long integer: 4246345689049834
4246345689049834 is invalid
Sample 2:
Enter a credit card number as a long integer: 4388576018410707
4388576018410707 is valid
Explanation / Answer
Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts. Thanks
// CreditCardValidator.java
import java.util.Scanner;
public class CreditCardValidator {
/**
* a helper method to find the sum of digits of a given number
*/
static int sumDigits(int num) {
int sum = 0;
while (num > 0) {
int dig = num % 10;
num = num / 10;
sum += dig;
}
return sum;
}
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.print("Enter a credit card number: ");
/**
* getting input
*/
long input = Long.parseLong(scanner.nextLine());
int singleDigitsSum = 0;// to keep the sum of calculated single digits
int oddSum = 0; // to keep the sum of digits at odd places
long temp = input;// copying the input number
boolean oddPlace = true;// to denote if the loop is processing a value
// at odd place now
/**
* looping until the value is not greater than 0
*/
while (temp > 0) {
//extracting the digit
int digit = (int) (temp % 10);
//removing the digit from number
temp = temp / 10;
//checking if the current position is odd
if (oddPlace) {
//adding to odd sum
oddSum += digit;
} else {
//finding the double of this digit
int doubled = digit * 2;
//converting to single digit sum if double is above 9
if (doubled > 9) {
doubled = sumDigits(doubled);
}
//adding to single digits sum
singleDigitsSum += doubled;
}
//negating the value of oddPlace for the next iteration
oddPlace = !oddPlace;
}
//finding the sum
int sum = singleDigitsSum + oddSum;
//if sum is divisible by 10, its a valid number
if (sum % 10 == 0) {
System.out.println(input + " is valid");
} else {
System.out.println(input + " is not valid");
}
}
}
/*OUTPUT*/
Enter a credit card number: 4246345689049834
4246345689049834 is not valid
Enter a credit card number: 4388576018410707
4388576018410707 is valid
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