server,服务器代码。
使用Socket套接字连接。

using System;
using System.Net;
using System.Net.Sockets;
using System.IO ;

public class Echoserver
{
//entry point of main method.
public static void Main()
{
//TcpListener is listening on the given port
Int32 port = 1234;

//IPAddress is connetct ip address
//IPAddress addr = IPAddress.Parse("127.0.0.1");
IPAddress ipAddress = Dns.Resolve("localhost").AddressList[0];

TcpListener tcpListener = new TcpListener(ipAddress,port);
tcpListener.Start();
Console.WriteLine("Server Started") ;
//Accepts a new connection
Socket socketForClient = tcpListener.AcceptSocket();
//StreamWriter and StreamReader Classes for reading and writing the data to and from.
//The server reads the meassage sent by the Client ,converts it to upper case and sends it back to the client.
//Lastly close all the streams.
try
{
if (socketForClient.Connected)
{
while(true)
{
Console.WriteLine("Client connected");
NetworkStream networkStream = new NetworkStream(socketForClient);
StreamWriter streamWriter = new StreamWriter(networkStream);
StreamReader streamReader = new StreamReader(networkStream);
string line = streamReader.ReadLine();
Console.WriteLine("Read:" +line);
line=line.ToUpper()+ "!";
streamWriter.WriteLine(line);
Console.WriteLine("Wrote:"+line);
streamWriter.Flush() ;
}
}
socketForClient.Close();
Console.WriteLine("Exiting");
}
catch(Exception e)
{
Console.WriteLine(e.ToString()) ;
}
}
}

Client,客户端程序，在文本框中输入字符，将在列表框显示。
using System;
using System.Text;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Net;
using System.Net.Sockets;
using System.IO;

namespace SocketSample
{
public class Sample : System.Windows.Forms.Form
{
private System.Windows.Forms.Button btS;
private System.Windows.Forms.TextBox t1;
private NetworkStream networkStream ;
private StreamReader streamReader ;
private StreamWriter streamWriter ;
ArrayList sb;
TcpClient myclient;
bool flag=false;
private System.Windows.Forms.ListBox t2;

private System.ComponentModel.Container components = null;

public Sample()
{
sb = new ArrayList();
InitializeComponent();
if(!flag)
Connect();

//get a Network stream from the server
networkStream = myclient.GetStream();
streamReader = new StreamReader(networkStream);
streamWriter = new StreamWriter(networkStream);
ShowMessage();
}

protected override void Dispose( bool disposing )
{
if( disposing )
{
if(components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}

Windows 窗体设计器生成的代码#region Windows 窗体设计器生成的代码
/**////

/// 设计器支持所需的方法 - 不要使用代码编辑器修改
/// 此方法的内容。
///

private void InitializeComponent()
{
System.Resources.ResourceManager resources = new System.Resources.ResourceManager(typeof(Sample));
this.t1 = new System.Windows.Forms.TextBox();
this.btS = new System.Windows.Forms.Button();
this.t2 = new System.Windows.Forms.ListBox();
this.SuspendLayout();
//
// t1
//
this.t1.Location = new System.Drawing.Point(24, 32);
this.t1.Name = "t1";
this.t1.Size = new System.Drawing.Size(280, 21);
this.t1.TabIndex = 0;
this.t1.Text = "";
this.t1.TextChanged += new System.EventHandler(this.t1_TextChanged);
//
// btS
//
this.btS.BackgroundImage = ((System.Drawing.Image)(resources.GetObject("btS.BackgroundImage")));
this.btS.Enabled = false;
this.btS.FlatStyle = System.Windows.Forms.FlatStyle.Popup;
this.btS.Location = new System.Drawing.Point(320, 32);
this.btS.Name = "btS";
this.btS.TabInd