C#

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Net;
using System.Net.Sockets;
using System.Text;

namespace Asynchronous_Server
{
	/// <summary>
	/// Summary description for Form1.
	/// </summary>
	public class Form1 : System.Windows.Forms.Form
	{
		Socket server = new Socket(AddressFamily.InterNetwork,SocketType.Stream, ProtocolType.Tcp);
		IPEndPoint iep = new IPEndPoint(IPAddress.Any, 5020);
		private byte[] data = new byte[1024];
		private int size = 1024;
		private System.Windows.Forms.TextBox conStatus;
		private System.Windows.Forms.ListBox results;
		/// <summary>
		/// Required designer variable.
		/// </summary>
		private System.ComponentModel.Container components = null;
		
		public Form1()
		{
			//
			// Required for Windows Form Designer support
			//
			InitializeComponent();

			//
			// TODO: Add any constructor code after InitializeComponent call
			//

		}

		/// <summary>
		/// Clean up any resources being used.
		/// </summary>
		protected override void Dispose( bool disposing )
		{
			if( disposing )
			{
				if (components != null) 
				{
					components.Dispose();
				}
			}
			base.Dispose( disposing );
		}

		#region Windows Form Designer generated code
		/// <summary>
		/// Required method for Designer support - do not modify
		/// the contents of this method with the code editor.
		/// </summary>
		private void InitializeComponent()
		{
            this.results = new System.Windows.Forms.ListBox();
            this.conStatus = new System.Windows.Forms.TextBox();
            this.SuspendLayout();
            // 
            // results
            // 
            this.results.BackColor = System.Drawing.Color.AliceBlue;
            this.results.Dock = System.Windows.Forms.DockStyle.Fill;
            this.results.Font = new System.Drawing.Font("Microsoft Sans Serif", 8.25F, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, ((byte)(178)));
            this.results.Items.AddRange(new object[] {
            "Clients Transmissions ..."});
            this.results.Location = new System.Drawing.Point(0, 0);
            this.results.Name = "results";
            this.results.Size = new System.Drawing.Size(288, 174);
            this.results.TabIndex = 0;
            this.results.SelectedIndexChanged += new System.EventHandler(this.results_SelectedIndexChanged);
            // 
            // conStatus
            // 
            this.conStatus.BackColor = System.Drawing.Color.Gainsboro;
            this.conStatus.BorderStyle = System.Windows.Forms.BorderStyle.FixedSingle;
            this.conStatus.Dock = System.Windows.Forms.DockStyle.Bottom;
            this.conStatus.Font = new System.Drawing.Font("Microsoft Sans Serif", 9F, System.Drawing.FontStyle.Italic, System.Drawing.GraphicsUnit.Point, ((byte)(178)));
            this.conStatus.Location = new System.Drawing.Point(0, 153);
            this.conStatus.Name = "conStatus";
            this.conStatus.ReadOnly = true;
            this.conStatus.Size = new System.Drawing.Size(288, 21);
            this.conStatus.TabIndex = 1;
            this.conStatus.Text = "Waiting for client...";
            // 
            // Form1
            // 
            this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
            this.ClientSize = new System.Drawing.Size(288, 174);
            this.Controls.Add(this.conStatus);
            this.Controls.Add(this.results);
            this.Name = "Form1";
            this.Text = "Asynchronous Server";
            this.Load += new System.EventHandler(this.Form1_Load);
            this.ResumeLayout(false);
            this.PerformLayout();

		}
		#endregion

		/// <summary>
		/// The main entry point for the application.
		/// </summary>
		[STAThread]
		static void Main() 
		{
			Application.Run(new Form1());
			
		}

		void AcceptConn(IAsyncResult iar)
		{
			Socket oldserver = (Socket)iar.AsyncState;
			Socket client = oldserver.EndAccept(iar);
			conStatus.Text = "Connected to: " + client.RemoteEndPoint.ToString();
			string stringData = "Welcome to my server";
			byte[] message1 = Encoding.ASCII.GetBytes(stringData);
			client.BeginSend(message1, 0, message1.Length, SocketFlags.None,new AsyncCallback(SendData), client);
            server.BeginAccept(new AsyncCallback(AcceptConn), server);
        }
		void SendData(IAsyncResult iar)
		{
			Socket client = (Socket)iar.AsyncState;
			int sent = client.EndSend(iar);
			client.BeginReceive(data, 0, size, SocketFlags.None,new AsyncCallback(ReceiveData), client);
		}
		void ReceiveData(IAsyncResult iar)
		{
			Socket client = (Socket)iar.AsyncState;
			int recv = client.EndReceive(iar);
			if (recv == 0)
			{
				client.Close();
				conStatus.Text = "Waiting for client...";
				server.BeginAccept(new AsyncCallback(AcceptConn), server);
				return;
			}
			string receivedData = Encoding.ASCII.GetString(data, 0, recv);
			results.Items.Add(receivedData);
			byte[] message2 = Encoding.ASCII.GetBytes(receivedData);
			client.BeginSend(message2, 0, message2.Length, SocketFlags.None,new AsyncCallback(SendData), client);
		}
		void ButtonStopOnClick(object obj, EventArgs ea)
		{
			Close();
		}

		private void Form1_Load(object sender, System.EventArgs e)
		{
			server = new Socket(AddressFamily.InterNetwork,SocketType.Stream, ProtocolType.Tcp);
			IPEndPoint iep = new IPEndPoint(IPAddress.Any, 5020);
			server.Bind(iep);
			server.Listen(-1);
			server.BeginAccept(new AsyncCallback(AcceptConn), server);
		}

        private void results_SelectedIndexChanged(object sender, EventArgs e)
        {

        }

	}
}

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Net;
using System.Net.Sockets;
using System.Text;

namespace ASyn_Client_Example
{
	/// <summary>
	/// Summary description for Form1.
	/// </summary>
	public class Form1 : System.Windows.Forms.Form
	{
		private Socket client;
		private byte[] data = new byte[1024];
		private int size = 1024;

		private System.Windows.Forms.Button button1;
		private System.Windows.Forms.TextBox newText;
		private System.Windows.Forms.ListBox results;
		private System.Windows.Forms.Button button2;
		private System.Windows.Forms.Button button3;
		private System.Windows.Forms.TextBox conStatus;
		private System.Windows.Forms.TextBox textBox1;
		/// <summary>
		/// Required designer variable.
		/// </summary>
		private System.ComponentModel.Container components = null;

		public Form1()
		{
			//
			// Required for Windows Form Designer support
			//
			InitializeComponent();

			//
			// TODO: Add any constructor code after InitializeComponent call
			//
		}

		/// <summary>
		/// Clean up any resources being used.
		/// </summary>
		protected override void Dispose( bool disposing )
		{
			if( disposing )
			{
				if (components != null) 
				{
					components.Dispose();
				}
			}
			base.Dispose( disposing );
		}

		#region Windows Form Designer generated code
		/// <summary>
		/// Required method for Designer support - do not modify
		/// the contents of this method with the code editor.
		/// </summary>
		private void InitializeComponent()
		{
            this.button1 = new System.Windows.Forms.Button();
            this.newText = new System.Windows.Forms.TextBox();
            this.results = new System.Windows.Forms.ListBox();
            this.button2 = new System.Windows.Forms.Button();
            this.button3 = new System.Windows.Forms.Button();
            this.conStatus = new System.Windows.Forms.TextBox();
            this.textBox1 = new System.Windows.Forms.TextBox();
            this.SuspendLayout();
            // 
            // button1
            // 
            this.button1.Enabled = false;
            this.button1.FlatStyle = System.Windows.Forms.FlatStyle.Popup;
            this.button1.Location = new System.Drawing.Point(328, 24);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(75, 56);
            this.button1.TabIndex = 0;
            this.button1.Text = "Send";
            this.button1.Click += new System.EventHandler(this.button1_Click);
            // 
            // newText
            // 
            this.newText.BackColor = System.Drawing.Color.Azure;
            this.newText.Location = new System.Drawing.Point(16, 24);
            this.newText.Name = "newText";
            this.newText.ReadOnly = true;
            this.newText.Size = new System.Drawing.Size(304, 20);
            this.newText.TabIndex = 1;
            this.newText.KeyPress += new System.Windows.Forms.KeyPressEventHandler(this.newText_KeyPress);
            // 
            // results
            // 
            this.results.BackColor = System.Drawing.Color.LightCyan;
            this.results.Location = new System.Drawing.Point(16, 56);
            this.results.Name = "results";
            this.results.Size = new System.Drawing.Size(304, 95);
            this.results.TabIndex = 2;
            this.results.SelectedIndexChanged += new System.EventHandler(this.results_SelectedIndexChanged);
            // 
            // button2
            // 
            this.button2.Enabled = false;
            this.button2.FlatStyle = System.Windows.Forms.FlatStyle.Popup;
            this.button2.Location = new System.Drawing.Point(328, 128);
            this.button2.Name = "button2";
            this.button2.Size = new System.Drawing.Size(75, 24);
            this.button2.TabIndex = 3;
            this.button2.Text = "Disconnect";
            this.button2.Click += new System.EventHandler(this.button2_Click);
            // 
            // button3
            // 
            this.button3.FlatStyle = System.Windows.Forms.FlatStyle.Popup;
            this.button3.Location = new System.Drawing.Point(328, 160);
            this.button3.Name = "button3";
            this.button3.Size = new System.Drawing.Size(75, 24);
            this.button3.TabIndex = 4;
            this.button3.Text = "Connect";
            this.button3.Click += new System.EventHandler(this.button3_Click);
            // 
            // conStatus
            // 
            this.conStatus.BackColor = System.Drawing.SystemColors.InactiveBorder;
            this.conStatus.BorderStyle = System.Windows.Forms.BorderStyle.FixedSingle;
            this.conStatus.Dock = System.Windows.Forms.DockStyle.Bottom;
            this.conStatus.Font = new System.Drawing.Font("Microsoft Sans Serif", 9F, System.Drawing.FontStyle.Italic, System.Drawing.GraphicsUnit.Point, ((byte)(178)));
            this.conStatus.Location = new System.Drawing.Point(0, 187);
            this.conStatus.Name = "conStatus";
            this.conStatus.Size = new System.Drawing.Size(408, 21);
            this.conStatus.TabIndex = 5;
            this.conStatus.Text = "Disconnected";
            // 
            // textBox1
            // 
            this.textBox1.BackColor = System.Drawing.Color.Azure;
            this.textBox1.Location = new System.Drawing.Point(16, 160);
            this.textBox1.Name = "textBox1";
            this.textBox1.Size = new System.Drawing.Size(304, 20);
            this.textBox1.TabIndex = 6;
            this.textBox1.Text = "127.0.0.1";
            // 
            // Form1
            // 
            this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
            this.BackColor = System.Drawing.SystemColors.Control;
            this.ClientSize = new System.Drawing.Size(408, 208);
            this.Controls.Add(this.textBox1);
            this.Controls.Add(this.conStatus);
            this.Controls.Add(this.newText);
            this.Controls.Add(this.button3);
            this.Controls.Add(this.button2);
            this.Controls.Add(this.results);
            this.Controls.Add(this.button1);
            this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedSingle;
            this.MaximizeBox = false;
            this.Name = "Form1";
            this.StartPosition = System.Windows.Forms.FormStartPosition.CenterScreen;
            this.Text = "Asynchronous Client";
            this.Load += new System.EventHandler(this.Form1_Load);
            this.ResumeLayout(false);
            this.PerformLayout();

		}
		#endregion

		/// <summary>
		/// The main entry point for the application.
		/// </summary>
		[STAThread]
		static void Main() 
		{
			Application.Run(new Form1());
		}
		void ReceiveData(IAsyncResult iar)
		{
			try
			{
			Socket remote = (Socket)iar.AsyncState;
			int recv = remote.EndReceive(iar);
			string stringData = Encoding.ASCII.GetString(data, 0, recv);
			results.Items.Add(stringData);
			}
			catch(Exception ex){MessageBox.Show(ex.Message);}

			}
		void SendData(IAsyncResult iar)
		{
			try
			{
			Socket remote = (Socket)iar.AsyncState;
			int sent = remote.EndSend(iar);
			remote.BeginReceive(data, 0, size, SocketFlags.None,
				new AsyncCallback(ReceiveData), remote);
			}
			catch(Exception ex){MessageBox.Show(ex.Message);}

			}

		void Connected(IAsyncResult iar)
		{
			client = (Socket)iar.AsyncState;
			try
			{
				client.EndConnect(iar);
				conStatus.Text = "Connected to: " + client.RemoteEndPoint.ToString();
				client.BeginReceive(data, 0, size, SocketFlags.None,
					new AsyncCallback(ReceiveData), client);
			} 
			catch (SocketException)
			{
				conStatus.Text = "Error connecting";
			}
		}
		private void Form1_Load(object sender, System.EventArgs e)
		{
		
		}

		private void button1_Click(object sender, System.EventArgs e)
		{
			try
			{
				byte[] message = Encoding.ASCII.GetBytes(newText.Text);
				newText.Clear();
				client.BeginSend(message, 0, message.Length, SocketFlags.None,new AsyncCallback(SendData), client);
				newText.Focus();
			}
			catch(Exception ex){MessageBox.Show(ex.Message);}
		}

		private void button3_Click(object sender, System.EventArgs e)
		{
		try
		{
			conStatus.Text = "Connecting...";
			Socket newsock = new Socket(AddressFamily.InterNetwork,
			SocketType.Stream, ProtocolType.Tcp);
			IPEndPoint iep = new IPEndPoint(IPAddress.Parse(textBox1.Text), 5020);
			newsock.BeginConnect(iep, new AsyncCallback(Connected), newsock);
			newText.Focus();
			button1.Enabled = true;
			button2.Enabled = true;
			newText.ReadOnly = false;

		}
		catch(Exception ex){MessageBox.Show(ex.Message);}

		}

		private void button2_Click(object sender, System.EventArgs e)
		{
			client.Close();
			button1.Enabled = false;
			button2.Enabled = false;
			newText.ReadOnly = true;
			conStatus.Text = "Disconnected";
		}

		private void newText_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
		{
			if (button1.Enabled == true)
			if(e.KeyChar == '\r')
			{
				button1_Click(sender,e);
			}
		}

        private void results_SelectedIndexChanged(object sender, EventArgs e)
        {

        }
	}
}

conStatus.Text = "Connected to: " + client.RemoteEndPoint.ToString();