Check Digit based on modulo 11 - c#

Modulus11.cs

public class Modulus11
{
    public string GetCheckDigit(string number)
    {
        int sum = 0;
        for (int i = number.Length - 1, multiplier = 2; i >= 0; i--)
        {
            sum += (int)char.GetNumericValue(number[i]) * multiplier;
            if (++multiplier > 9) multiplier = 2;
        }
        int mod = (sum % 11);
        if (mod == 0 || mod == 1) return "0";
        return (11 - mod).ToString();
    }
}

Hi martinusso, This only seems to work for numbers with 7 digits or fewer. I think the multiplier should be set back to 2 when it exceeds 7, not 9. But its a cool solution once that is sorted out. Thanks!