using System;

using System.Text;

​

public class Program

{

    public static void Main()

    {

        string input = "?Flow";

        Console.WriteLine("Input: " + input);

        Console.WriteLine("Output: " + Encoding.ASCII.GetString(CalcLRC(Encoding.ASCII.GetBytes(input))));

    }

​

    private static byte[] CalcLRC(byte[] cmnd)

    {

        int i, j, bSize = cmnd.Length;

        uint lrc, high, low, CR, LF;

        string temp;

        byte[] bytes = new byte[((bSize) + 4)];

        lrc = 0x00;

        CR = 0x0d;

        LF = 0x0a;

        //loop through input byte array

        for (i = 0; i < cmnd.Length; i++)

        {

            //sum message bytes

            lrc = lrc + (uint)cmnd[i];

            //insert each message byte into result

            bytes[i] = cmnd[i];

        }

​

        //remove remainder

        if (lrc > 256)

        {

            lrc = lrc - (uint)(256 * Math.Floor((double)lrc / 256));

        }

​

        //perform 2's complement on sum

        lrc = (ushort)(~lrc);

        lrc = lrc + 1;

        //remove remainder

        if (lrc > 256)

        {

            lrc = lrc - (uint)(256 * Math.Floor((double)lrc / 256));

        }

​

        //split into high and low bits

        temp = lrc.ToString("X");

        high = (uint)temp[0];

        low = (uint)temp[1];

        //insert high, low, carriage return, and line feed into result

        bytes[(bSize)] = (byte)high;

        bytes[(bSize + 1)] = (byte)low;

        bytes[(bSize + 2)] = (byte)CR;

        bytes[(bSize + 3)] = (byte)LF;

        //return result byte array with input, LRC, CR, LF

        return bytes;

    }

}