CPlusPlus/CreditCardValidator.cpp at main · JesseOgunlaja/CPlusPlus · GitHub

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#include <iostream>

int getDigit(const int number);
int sumOddDigits(const std::string cardNumber);
int sumEvenDigits(const std::string cardNumber);

int main()
{
    std::string cardNumber;
    int result = 0;

    std::cout << "Enter your credit card number: ";
    std::cin >> cardNumber;

    result = sumEvenDigits(cardNumber) + sumOddDigits(cardNumber);

    if(result % 10 == 0){
        std::cout << "You have a valid credit card number";
    }
    else {
        std::cout << "You have a invalid credit card number";
    }

    return 0;
}
int getDigit(const int number){

    return number % 10 + (number / 10 % 10);
}
int sumOddDigits(const std::string cardNumber){

    int sum = 0;

    for(int i = cardNumber.size() - 1; i >= 0; i-=2){
        sum += cardNumber[i] - '0';
    }

    return sum;
}
int sumEvenDigits(const std::string cardNumber){
    int sum = 0;

    for(int i = cardNumber.size() - 2; i >= 0; i-=2){
        sum += getDigit((cardNumber[i] - '0') * 2);
    }

    return sum;
}