int check_sin(int *sin_array) {

    int luhn_order[9] = {1,2,1,2,1,2,1,2,1};
    int sum = 0;
    int temp;

    for(int i = 0; i < 9; i ++){

        temp = sin_array[i] * luhn_order[i];

        if (temp < 10){
            sum += temp;
            printf("%d\n", temp);
        }
        else {
            printf("%d\n", temp);
            sum += temp % 10;
            temp /= 10;
            printf("%d\n", temp);
            sum += temp % 10;
        }

    }

    if(sum % 10 == 0){
        return 0;
    }

    return 1;
}
to multiply each element in sin_array by each element in luhn_order and sum up all the numbers