using System;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        string generatedNumber = "15100508854";

        string checkDigits = generatedNumber.Substring(4, 6);

        Console.WriteLine(checkDigits);

        int totalOfRemainders = 0;

        int multiplier = 7;

        for (int i = 0; i < checkDigits.Length; i++)

        {

            // Multiple the numbers

            int result = Convert.ToInt32(checkDigits[i].ToString()) * multiplier;

            Console.WriteLine(string.Format("Result {0} loop {1} multiplier {2}", result, i, multiplier));

            // Add the remainder mod 10 to the sum

            totalOfRemainders += (result % 10);

            multiplier--;

        }

​

        // Take the mod 10

        int modValue = totalOfRemainders % 10;

        int checkDigit = modValue > 0 ? 10 - modValue : 0;

        string checkStr = checkDigit.ToString();

        string lastCharacter = generatedNumber.Last().ToString();

        // Check if the last character is the same as the check digit

        // if not set to the check digit

        if (checkStr != lastCharacter)

        {

            generatedNumber = generatedNumber.Substring(0, 10) + checkStr;

            Console.WriteLine("Changed to " + generatedNumber);

        }

​

        Console.WriteLine("Hello World");

    }

}