C# Luhn CheckDigit generator - returns 10 instead of 0

Question

2.50/5 (2 votes)

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Hi all,

I've been trying to make a mod10 check digit calculator in C#. I've found a snippet that works, however, I cannot seem to find out how to tell the program to return 0 if the check digit is 10. It works for all other numbers except the ones that return 10. Can somebody please help me with where to insert this?

C#

public static int GetMod10Digit(string data)
        {
            int sum = 0;
            bool odd = true;
            for (int i = data.Length - 1; i >= 0; i--)
            {
                if (odd == true)
                {
                    int tSum = Convert.ToInt32(data[i].ToString()) * 2;
                    if (tSum >= 10)
                    {
                        string tData = tSum.ToString();
                        tSum = Convert.ToInt32(tData[0].ToString()) + Convert.ToInt32(tData[1].ToString());
                    }
                    sum += tSum;
                }
                else
                    sum += Convert.ToInt32(data[i].ToString());
                odd = !odd;
            }
            return (((sum / 10) + 1) * 10) - sum;
        }

Posted 21-Feb-11 0:27am

Jaykay832

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2 solutions

Solution 2

try this,

C#

public static int GetMod10Digit(string data)
{

 int sumOfDigits = data.Where((e) => e >= '0' && e <= '9')
 .Reverse()
 .Select((e, i) => ((int)e - 48) * (i % 2 == 0 ? 1 : 2))
 .Sum((e) => e / 10 + e % 10);
 //// If the final sum is divisible by 10, then the credit card number is valid. If it is not divisible by 10, the number is invalid.
 return sumOfDigits % 10;
}

Posted 2-Jan-13 20:03pm

Tharaka MTR

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OriginalGriff · Accepted Answer · 2011-02-21T00:40:00

Solution 1

Use the Modulus operator: "x % 10" will return 0 if x == 10.

Posted 21-Feb-11 0:40am

OriginalGriff

Comments

Jaykay832 21-Feb-11 6:46am

Thank you for the suggestion. Could you please show me where I need to set this in the code?

OriginalGriff 21-Feb-11 6:50am

Since mod10 is supposed to always return a number if the range 0 to 9, I would recommend you think about the "return" statement?

Possibly change it to:

int result = (((sum / 10) + 1) * 10) - sum;
return result % 10;

Just a thought...

Jaykay832 21-Feb-11 6:53am

Works perfect! Thank you so much.

OriginalGriff 21-Feb-11 6:55am

Welcome!

Sergey Alexandrovich Kryukov 21-Feb-11 21:50pm

5, Your Patience,
--SA