TCP zwischen C und C#

private void listen_tcp()

        {

            IPAddress ipAddress = IPAddress.Any;

            TcpListener listener = new TcpListener(ipAddress, 12345);

            listener.Start();

            Console.WriteLine("Server is running");

            Console.WriteLine("Listening on port " + 12345);

            Console.WriteLine("Waiting for connections...");

            label15.Text = "test";

            while (true)

            {

                Socket s = listener.AcceptSocket();

                Console.WriteLine("Connection accepted from " + s.RemoteEndPoint);

                byte[] b = new byte[20];

                int k = s.Receive(b);

                Console.WriteLine("Received:");

                for (int i = 0; i < k; i++)

                    Console.Write(Convert.ToChar(b[i]));

                ASCIIEncoding enc = new ASCIIEncoding();

                s.Send(enc.GetBytes("Server responded"));

                Console.WriteLine("\nSent Response");

                s.Close();

            }

            }

WSADATA wsa;

  SOCKET mysocket;

  SOCKADDR_IN addr;

  long rc;

  char mystring[20] = "Hallo\n";

  if(WSAStartup(MAKEWORD(2,0),&wsa)!=0) 

    printf("Winsock konnte nicht gestartet werden\n");

  else

    printf("Winsock gestartet\n");

  mysocket=socket(AF_INET,SOCK_STREAM,0);

  if(mysocket==INVALID_SOCKET)

  {

    printf("Fehler: Der Socket konnte nicht erstellt werden, fehler code: %d\n",WSAGetLastError());

    return 1;

  }

  else

  {

    printf("Socket erstellt!\n");

  }

  memset(&addr,0,sizeof(SOCKADDR_IN));

  addr.sin_family=AF_INET;

  addr.sin_port=htons(12345); // wir verwenden mal port 12345

  addr.sin_addr.s_addr=inet_addr("127.0.0.1"); // zielrechner ist unser eigener

  rc=connect(mysocket,(SOCKADDR*)&addr,sizeof(SOCKADDR));

  if(rc==SOCKET_ERROR)

  {

    printf("Fehler: connect gescheitert, fehler code: %d\n",WSAGetLastError());

    return 1;

  }

  else

  {

    printf("Verbunden mit 127.0.0.1..\n");

  }

  send(mysocket,mystring,sizeof(mystring),0);

  strcpy(mystring,"Welt");

  send(mysocket,mystring,9,0);