Task: Echo server
C: #include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <unistd.h>
#include <sys/wait.h>
#include <signal.h>

#define MAX_ENQUEUED 20
#define BUF_LEN 256
#define PORT_STR "12321"





void wait_for_zombie(int s)
{
    while(waitpid(-1, NULL, WNOHANG) > 0) ;
}





void echo_lines(int csock)
{
    char buf[BUF_LEN];
    int r;

    while( (r = read(csock, buf, BUF_LEN)) > 0 ) {
        (void)write(csock, buf, r);
    }
    exit(EXIT_SUCCESS);
}





void take_connections_forever(int ssock)
{
    for(;;) {
        struct sockaddr addr;
        socklen_t addr_size = sizeof(addr);
        int csock;

        
        csock = accept(ssock, &addr, &addr_size);

        
        if ( csock == -1 ) {
            perror("accept");
        } else if ( fork() == 0 ) {
            close(ssock);
            echo_lines(csock);
        } else {
            close(csock);
        }
    }
}





int main()
{
    struct addrinfo hints, *res;
    struct sigaction sa;
    int sock;

    
    memset(&hints, 0, sizeof(struct addrinfo));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_PASSIVE;
    if ( getaddrinfo(NULL, PORT_STR, &hints, &res) != 0 ) {
        perror("getaddrinfo");
        exit(EXIT_FAILURE);
    }

    
    if ( (sock = socket(res->ai_family, res->ai_socktype, res->ai_protocol)) == -1 ) {
        perror("socket");
        exit(EXIT_FAILURE);
    }

    
    sa.sa_handler = wait_for_zombie;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART;
    if ( sigaction(SIGCHLD, &sa, NULL) == -1 ) {
        perror("sigaction");
        exit(EXIT_FAILURE);
    }

    
    if ( bind(sock, res->ai_addr, res->ai_addrlen) != 0 ) {
        perror("bind");
        exit(EXIT_FAILURE);
    }

    freeaddrinfo(res);

    
    if ( listen(sock, MAX_ENQUEUED) != 0 ) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    
    take_connections_forever(sock);
    return EXIT_SUCCESS;
}

C#: using System.Net.Sockets;
using System.Threading;

namespace ConsoleApplication1
{
    class Program
    {
        static TcpListener listen;
        static Thread serverthread;

        static void Main(string[] args)
        {
            listen = new TcpListener(System.Net.IPAddress.Parse("127.0.0.1"), 12321);
            serverthread = new Thread(new ThreadStart(DoListen));
            serverthread.Start();
        }

        private static void DoListen()
        {
            
            listen.Start();
            Console.WriteLine("Server: Started server");

            while (true)
            {
                Console.WriteLine("Server: Waiting...");
                TcpClient client = listen.AcceptTcpClient();
                Console.WriteLine("Server: Waited");

                
                Thread clientThread = new Thread(new ParameterizedThreadStart(DoClient));
                clientThread.Start(client);
            }
        }

        private static void DoClient(object client)
        {
            
            TcpClient tClient = (TcpClient)client;

            Console.WriteLine("Client (Thread: {0}): Connected!", Thread.CurrentThread.ManagedThreadId);
            do
            {
                if (!tClient.Connected)
                { 
                    tClient.Close();
                    Thread.CurrentThread.Abort();       
                }

                if (tClient.Available > 0)
                {
                    
                    byte pByte = (byte)tClient.GetStream().ReadByte();
                    Console.WriteLine("Client (Thread: {0}): Data {1}", Thread.CurrentThread.ManagedThreadId, pByte);
                    tClient.GetStream().WriteByte(pByte);
                }

                
                Thread.Sleep(100);
            } while (true);
        }
    }
}