using System;

public class Program

{

    public static void Main()

    {

        ITransactionCodeGenerator generator = new TransactionCodeGenerator();

        var code = generator.GenerateCode(14);

        Console.WriteLine(code);

    }

}

​

public class TransactionCodeGenerator : ITransactionCodeGenerator

    {

        public string GenerateCode(int prefix)

        {

            var fromNumber = 1000000;

            var toNumber = 9999999;

​

            Random rnd = new Random(Guid.NewGuid().GetHashCode());

            int number = rnd.Next(fromNumber, toNumber);

            Console.WriteLine(prefix.ToString("D2"));

            Console.WriteLine(number);

​

            long digit = number.Checksum_ean8();

            Console.WriteLine(digit);

​

            long code = (number * (long)10) + digit;

​

            return prefix.ToString("D2")+code.ToString();

        }

    }

public interface ITransactionCodeGenerator

    {

        string GenerateCode(int prefix);

    }

​

public static class EAN8CheckSum

    {

        public static int Checksum_ean8(this int number)

        {

            var data = number.ToString();

​

            // Test string for correct length

            if (data.Length != 7 && data.Length != 8)

                return -1;

​

            // Test string for being numeric

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

            {

                if (data[i] < 0x30 || data[i] > 0x39)

                    return -1;

            }

​

            int sum = 0;

​

            for (int i = 6; i >= 0; i--)

            {

                int digit = data[i] - 0x30;

                if ((i & 0x01) == 1)

                    sum += digit;

                else

                    sum += digit * 3;

            }

            int mod = sum % 10;

            return mod == 0 ? 0 : 10 - mod;

        }

    }