client.c

#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <netinet/in.h>
#include <sys/time.h>
#include <sys/types.h>

#define TRUE                1
#define FALSE               0

int main(int argc , char *argv[])
{
    int sock, max_fds, activity;
    struct sockaddr_in server;
    char msg[1000], sreply[2000];
    fd_set readfds, writefds;

    sock = socket(AF_INET, SOCK_STREAM, 0);
    if (sock==-1) {
        printf("error: Could not create socket");
    }
    puts("info: socket created");

    server.sin_addr.s_addr = inet_addr(argv[1]);
    server.sin_family = AF_INET;
    server.sin_port = htons(atoi(argv[2]));

    if (connect(sock, (struct sockaddr *)&server, sizeof(server))<0) {
        perror("error: connect failed. Error");
        return 1;
    }
    puts("info: Connected\n");

    //keep communicating with server
    while(1) {
        FD_ZERO(&readfds);
        FD_SET(sock, &readfds);
        FD_SET(0, &readfds);

        max_fds=sock;
        printf("\rme: ");
        fflush(stdout);

        activity = select(max_fds+1, &readfds , NULL , NULL , NULL);

        if ((activity<0) && (errno!=EINTR)) {
            printf("error: select error");
        }
        if (FD_ISSET(sock, &readfds)) {
            if(recv(sock, sreply, sizeof(sreply),0)>0) {
                printf("\r%s",sreply);
                fflush(stdout);
                memset(sreply,0,sizeof(sreply));
            }
        }
        if (FD_ISSET(0, &readfds)) {
            memset(msg,0,sizeof(msg));
            fgets(msg, sizeof(msg) - 1, stdin);
            fflush(stdout);
        }
        if(send(sock,msg,strlen(msg),0) < 0) {
            puts("error: Send failed");
            return 1;
        }
        memset(msg,0,sizeof(msg));
    }
    close(sock);
    return 0;
}

server.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/time.h>

#define TRUE                                1
#define FALSE                               0
#define PORT                                0
#define MAX                                 30

int main(int argc , char *argv[])
{
    int opt = TRUE;
    int ss, addrlen, ns, cs[MAX], activity, i, val, sd, new_socket, j;
    int max_fds;
    struct sockaddr_in address;

    char buffer[MAX][1025];
    char client_id_buf[2055];
    fd_set readfds;
    char *message ="Welcome Clients.\n";
    memset(cs, 0, MAX*sizeof(cs[0]));
    if((ss = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }
    if(setsockopt(ss, SOL_SOCKET, SO_REUSEADDR, (char *)&opt, sizeof(opt)) < 0) {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }

    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);

    if (bind(ss, (struct sockaddr *)&address, sizeof(address)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    if (listen(ss, 3) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }
    int tmp_len = sizeof(address);
    if (getsockname(ss, (struct sockaddr*)&address, &tmp_len) == -1) {
        perror("getsockname");
    }
    else {
        printf("Listener on port %d \n", ntohs(address.sin_port));
    }


    addrlen = sizeof(address);
    puts("Waiting for connections ...");

    while(TRUE) {
        FD_ZERO(&readfds);
        FD_SET(ss, &readfds);
        max_fds = ss;
        for (i = 0; i < MAX; i++)
        {
            sd = cs[i];
            if(sd > 0)
                FD_SET(sd, &readfds);
            if(sd > max_fds)
                max_fds = sd;
        }

        activity = select(max_fds + 1, &readfds , NULL , NULL , NULL);

        if ((activity < 0) && (errno != EINTR))
        {
            printf("select error");
        }

        if (FD_ISSET(ss, &readfds)) {
            if ((ns = accept(ss, (struct sockaddr *)&address, (socklen_t*)&addrlen)) < 0)
            {
                perror("accept");
                exit(EXIT_FAILURE);
            }
            printf("New connection , socket fd is %d , ip is : %s , port : %d \n" , new_socket , inet_ntoa(address.sin_addr) , ntohs(address.sin_port));


            if(send(ns, message, strlen(message), 0) != strlen(message)) {
                perror("send");
            }

            puts("Welcome message sent successfully");

            for (i = 0;i < MAX; i++)
            {
                if(cs[i] == 0)
                {
                    cs[i] = ns;
                    printf("Adding to list of sockets as %d\n", i);
                    break;
                }
            }
        }

        for (i =0; i < MAX; i++)
        {
            sd = cs[i];
            if (sd > 0) {
                if (FD_ISSET(sd, &readfds)) {
                    if ((val = recv(sd, buffer[i], 1024, 0)) == 0) {
                        getpeername(sd, (struct sockaddr*)&address, (socklen_t*)&addrlen);
                        printf("Host disconnected , ip %s , port %d \n" , inet_ntoa(address.sin_addr), ntohs(address.sin_port));
                        close(sd);
                        cs[i] = 0;
                    }
                    else {
                        for (j = 0; j < MAX; ++j) {
                            if (cs[j] > 0 && j != i) {
                                sprintf(client_id_buf, "client %d: %s", cs[i], buffer[i]);
                                send(cs[j], client_id_buf, strlen(client_id_buf), 0);
                            }
                        }
                    }
                }
            }
            memset(buffer[i], 0, sizeof(buffer[i]));
        }
    }
    return 0;
}

compilation comands

gcc client.c -std=c11 -o client
gcc server.c -std=c11 -o server