问针对英国商家的信用卡验证资源

EN

public static bool IsLuhnValid(string cardNumber) {
    if (string.IsNullOrEmpty(cardNumber))
        return false;
    Int64 cardNumberAsBigInt;
    if (!Int64.TryParse(cardNumber, out cardNumberAsBigInt) || (cardNumberAsBigInt == 0))
        return false;
    int indicator = 1;
    int firstNumberToAdd = 0;
    int secondNumberToAdd = 0;
    for (int i = cardNumber.Length - 1; i >= 0; i--) {
        int currentNumber = int.Parse(cardNumber[i].ToString());
        if (indicator == 1) {
            firstNumberToAdd += currentNumber;
            indicator = 0;
        }
        else {
            int doubleCurrentNumber = currentNumber + currentNumber;
            if (doubleCurrentNumber >= 10) {
                int num1 = Convert.ToInt32(doubleCurrentNumber.ToString().Substring(0, 1));
                int num2 = Convert.ToInt32(doubleCurrentNumber.ToString().Substring(1, 1));
                secondNumberToAdd += num1 + num2;
            }
            else {
                secondNumberToAdd += doubleCurrentNumber;
            }
            indicator = 1;
        }
    }
    return ((firstNumberToAdd + secondNumberToAdd) % 10 == 0);
}