Object Refference is Not Set to an Instance of an Object

[macai]

I am new to C#, and I've tried what seems to be everything, and the error Object Refference is Not Set to an Instance of an Object. I'm using the Mono C# compiler and here is the complete code to my program thus far. Can anyone tell me what's wrong?

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

// Program start class

public class Users {
		public Users() {
			public TcpClient client = new TcpClient();
			public bool LoggedOn = false;
			public NetworkStream stream = new NetworkStream();
		}	
	}




class Listener {
	
    // Main begins program execution.
    public static void Main() {
        Int32 port = 1337;
      	IPAddress localhost = IPAddress.Parse("127.0.0.1");
      	
        TcpListener listener = new TcpListener(localhost, port);
        listener.Start();
        bool program_run = true;
        int i = 0;
        int stream_len = 0;
		Users[] user = new Users[300];
        Byte[] bytes = new Byte[1024];
        string dat=" ";
        while (program_run) {
	        if (listener.Pending()) {
		        i=0;
		        while (!(user[i].LoggedOn)) {
			        i++;
			        }
		        user[i].LoggedOn=true;
		        user[i].client=listener.AcceptTcpClient();
		        user[i].stream=user[i].client.GetStream();
		        Console.WriteLine("Connected!");
		        
	        }
	        i=0;
	        while (i<301) {
		        if (user[i].LoggedOn) {
			        if (user[i].stream.Length>0) {
				        bytes = new Byte[user[i].stream.Length];
				        stream_len = user[i].stream.Read(bytes,0,stream_len);
				        
				        dat = Encoding.ASCII.GetBytes(bytes, 0, stream_len);
				        Console.WriteLine("Received Data: {0}", stream_len);
			        }
		        }
		        i=0;
	        }
        }
    }
}