Submission

[PPPPPPPPPP]

Score: 100

User: Jokul

Problemset: ตรวจบัตรเครดิต

Language: c

Time: 0.001 second

Submitted On: 2025-03-04 15:18:14

#include <stdio.h>

int main() {
    long long int c, result = 0;
    int n[16], i;
    scanf("%lld", &c);

    // Extract each digit of the credit card number into the array
    for (i = 15; i >= 0; i--) {
        n[i] = c % 10; // Get the last digit
        c = c / 10;    // Remove the last digit
    }

    // Apply the Luhn algorithm
    for (i = 14; i >= 0; i--) { // Start from the second last digit
        if (i % 2 == 0) { // Even index (1st, 3rd, 5th, etc. from the right)
            n[i] *= 2; // Double the digit
            if (n[i] > 9) {
                n[i] -= 9; // Subtract 9 if the result is greater than 9
            }
        }
    }

    // Calculate the sum of all digits
    for (i = 0; i < 15; i++) {
        result += n[i];
    }

    // Calculate the expected last digit
    int check_digit = (10 - (result % 10)) % 10;

    // Compare the calculated check digit with the last digit of the credit card number
    if (check_digit == n[15]) {
        printf("yes\n"); // Valid credit card number
    } else {
        printf("no\n"); // Invalid credit card number
    }

    return 0;
}