Luhn algorithm - Algorithm used to validate cards - raw dogging loops.

CardValidateAlgorithm.cpp

#include <iostream>

int main()
{
    std::string CardNumba;

    int CardNumbers[16];
    int SecondCardNumbers[8];

    int fullCardEq{};

    std::cout << "Gib card numba\n";
    std::cin >> CardNumba;

    if (CardNumba.length() != 16) {
        std::cout << "Card number must be 16 digits long!\n";
        return 1;
    }


    for (int i = 0; i < CardNumba.length(); i++) {
        CardNumbers[i] = CardNumba[i] - '0';
    }

    for (int i = 0; i < 16; i++) {
        int currentDigit = CardNumbers[i];

        if (i % 2 == 0) {
            currentDigit *= 2;
            if (currentDigit > 9) {
                currentDigit -= 9;
            }

        }

        fullCardEq += currentDigit;
    }

    if (fullCardEq % 10 == 0) {
        std::cout << "Valid card \n";
    }
    else {
        std::cout << "Bad card \n";
    }

    return 0;
}