C#

using System;
using System.ComponentModel;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.Xml;
using System.Windows.Forms;

namespace CallRecordingServer
{
    public class MessageReceiver
    {
        int tcpPort;

        private BackgroundWorker tcpThread = new BackgroundWorker();
        public delegate void ReadHandler(string MessageType, string MessageText);

        public event ReadHandler MessageRead;


        public MessageReceiver()
        {
            tcpPort = Convert.ToInt32(TaskTrayApplication.Properties.Settings.Default.tcpPort); //8083;

            tcpThread.WorkerReportsProgress = true;
            tcpThread.WorkerSupportsCancellation = true;

            tcpThread.DoWork += Thread_DoWork;
            tcpThread.ProgressChanged += tcpThread_ProgressChanged;
        }

        public void StartListening()
        {
            try
            {
                if (!tcpThread.IsBusy)
                {
                    tcpThread.RunWorkerAsync();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show("MessageReceiver", ex.Message);
            }
        }

        public void StopListening()
        {
            tcpThread.CancelAsync();
            Thread.Sleep(200);
        }




        void Thread_DoWork(Object sender, System.ComponentModel.DoWorkEventArgs e)
        {
            IPAddress ipLocalhost = IPAddress.Any;
            TcpListener tcpListener = new TcpListener(ipLocalhost, tcpPort);

            try
            {
                tcpListener.Start(100);
                while (!tcpThread.CancellationPending)
                {
                    while (!tcpListener.Pending() && !tcpThread.CancellationPending)
                    {
                        System.Windows.Forms.Application.DoEvents();
                        Thread.Sleep(10);
                    }

                    //check for cancel pending
                    if (tcpThread.CancellationPending)
                    {
                        break;
                    }

                    //open stream and receive data
                    TcpClient tcpClient = tcpListener.AcceptTcpClient();

                    NetworkStream netStream = tcpClient.GetStream();
                    StreamReader netStreamReader = new StreamReader(netStream);
                    StreamWriter netStreamWriter = new StreamWriter(netStream);
                    netStreamWriter.AutoFlush = true;
                    string stringData;

                    //report thread progress
                    stringData = netStreamReader.ReadToEnd();
                    tcpThread.ReportProgress(0, stringData);

                    //close stream
                    netStreamReader.Close();
                    netStream.Close();
                    
                    tcpClient.Close();

                }
            }

            catch (Exception ex)
            {

                //handle the exception outside the thread
                MessageBox.Show("MessageReceiver",ex.Message);
                tcpThread.ReportProgress(100, e);
            }
            finally
            {


                //stop the listener
                tcpListener.Stop();

            }

        }



        void tcpThread_ProgressChanged(Object sender, System.ComponentModel.ProgressChangedEventArgs e)
        {
            if (e.ProgressPercentage == 0)
            {
                //convert the xml to an object and fire public event
                try
                {
                    string xmlData = e.UserState.ToString();

                    XmlDocument doc = new XmlDocument();
                    doc.LoadXml(xmlData);
                    XmlNode root = doc.FirstChild;
                    string messageType = root.ChildNodes[0].InnerText;
                    string messageText = root.ChildNodes[1].InnerText;
                    MessageRead(messageType, messageText);
                }
                catch (Exception ex)
                {
                    string er = ex.Message;
                    MessageBox.Show(ex.Message);
                    //do nothing because we're disposing
                }
            }
            else
            {
                if (e.ProgressPercentage == 100)
                {
                    //could not connect
                    //displayError("Error with TCP connection: " & CType(e.UserState, Exception).Message)
                    tcpThread.CancelAsync();
                    Thread.Sleep(200);
                }
            }
        }

    }
}

delegate double GetGrade(SystemD SD);
GetGrade MyGrade;

MyGrade = new GetGrade(AreaGrade);
public double AreaGrade(SystemD SD)
{
return SD.Area;
}

MyGrade = new GetGrade(LengthGrade);
public double LengthGrade(SystemD SD)
{
return SD.Length;
}

MyGrade = new GetGrade(CustomGrade);
public double CustomGrade(SystemD SD)
{
   string str= CustomTextBox.Text;
   double Grade= CompileAndGetDoubleNumber(str,SD);  //This is the function that i want to implement. 
   // The function that i want gets the string that contain the code for calculation, and SD that represent the system(class instance). It's return the wanted value after the calculation, for example from the string '2*SD.Length+SD.Area' i will get a double that represent the value (2*Length +Area) of SD.
   return Grade;
}