int *result = malloc(sizeof(int) * 9); 
    for (int i = 0; i < 9; i++) {
        char **product;
        *product = sin_array[i] * luhn[i];

        if (product > 9) { // 2-digit number case
            result[i] = product[0] + product[1];
        }
        else {
            result[i] = product;
        }
    }
if product is a two digits, add up the digits