static void Main(string[] args) {
int[] cardNumber = new int[16];
Random rand = new Random();
for (int i = 0; i < 15; i++) {
cardNumber[i] = rand.Next(10);
for (int i = cardNumber.Length - 2; i >= 0; i--) {
int digit = cardNumber[i];
digit = (digit % 10) + 1;
int lastDigit = (10 - (sum % 10)) % 10;
cardNumber[15] = lastDigit;
Console.Write("Generated card number: ");
for (int i = 0; i < cardNumber.Length; i++) {
Console.Write(cardNumber[i]);