How to make a chat between two clients?

[Zuperman]

I have some C code of a server and a client, the client sends a message to server and receive back "Hello" + message. The server can treat more clients using select function. I want to modify this code to obtain a chat between two clients.
I have tried on client to make a fork, the child to receive new messages and the father to input messages but it doesn't seem to work, how can I sync the clients that when one sends a message the other one to be ready to receive?
This is the original code without modifications:
Server

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

#define PORT 2728

extern int errno;

char * conv_addr (struct sockaddr_in address)
{
  static char str[25];
  char port[7];

  strcpy (str, inet_ntoa (address.sin_addr));	

  bzero (port, 7);
  sprintf (port, ":%d", ntohs (address.sin_port));	
  strcat (str, port);
  return (str);
}

int sayHello(int fd)
{
  char buffer[100];		
  int bytes;			
  char msg[100];		
  char msgrasp[100]=" ";

  bytes = read (fd, msg, sizeof (buffer));
  if (bytes < 0)
    {
      perror ("read() error from client.\n");
      return 0;
    }
  printf ("[server] I've received the message...%s\n", msg);
        
  bzero(msgrasp,100);
  strcat(msgrasp,"Hello ");
  strcat(msgrasp,msg);
      
  printf("[server] Send back the message...%s\n",msgrasp);
      
  if (bytes && write (fd, msgrasp, bytes) < 0)
    {
      perror ("[server] write() error.\n");
      return 0;
    }
  
  return bytes;
}

int main ()
{
  struct sockaddr_in server;
  struct sockaddr_in from;
  fd_set readfds;	
  fd_set actfds;	
  struct timeval tv;	
  int sd, client;		
  int optval=1; 	
  int fd;	
  int nfds;		
  int len;	

  if ((sd = socket (AF_INET, SOCK_STREAM, 0)) == -1)
    {
      perror ("[server] socket() Error.\n");
      return errno;
    }

  setsockopt(sd, SOL_SOCKET, SO_REUSEADDR,&optval,sizeof(optval));

  bzero (&server, sizeof (server));

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

  if (bind (sd, (struct sockaddr *) &server, sizeof (struct sockaddr)) == -1)
    {
      perror ("[server] bind() Error.\n");
      return errno;
    }

  if (listen (sd, 5) == -1)
    {
      perror ("[server] listen() Error.\n");
      return errno;
    }
  
  FD_ZERO (&actfds);
  FD_SET (sd, &actfds);

  tv.tv_sec = 1;	
  tv.tv_usec = 0;
  
  nfds = sd;

  printf ("[server] Wait at port %d...\n", PORT);
  fflush (stdout);
        
  while (1)
    {
      bcopy ((char *) &actfds, (char *) &readfds, sizeof (readfds));

      if (select (nfds+1, &readfds, NULL, NULL, &tv) < 0)
	{
	  perror ("[server] select() Error.\n");
	  return errno;
	}
      if (FD_ISSET (sd, &readfds))
	{
	  len = sizeof (from);
	  bzero (&from, sizeof (from));
	  
	  client = accept (sd, (struct sockaddr *) &from, &len);

	  if (client < 0)
	    {
	      perror ("[server] accept() Error.\n");
	      continue;
	    }

          if (nfds < client)
            nfds = client;
            	 
	  FD_SET (client, &actfds);

	  printf("[server] Client with descriptor %d is connected from address %s.\n",client, conv_addr (from));
	  fflush (stdout);
	}    
      for (fd = 0; fd <= nfds; fd++)	
	{	 
	  if (fd != sd && FD_ISSET (fd, &readfds))
	    {	
	      if (sayHello(fd))
		{
		  printf ("[server] Client with descriptor %d has disconnected.\n",fd);
		  fflush (stdout);
		  close (fd);
		  FD_CLR (fd, &actfds);
		  
		}
	    }
	}			/* for */
    }				/* while */
}				/* main */

Client

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

extern int errno;

int port;

int main (int argc, char *argv[])
{
  int sd;			
  struct sockaddr_in server;
  char msg[100];		

  if (argc != 3)
    {
      printf ("[client] Sintax: %s <address_server> <port>\n", argv[0]);
      return -1;
    }

  port = atoi (argv[2]);

  if ((sd = socket (AF_INET, SOCK_STREAM, 0)) == -1)
    {
      perror ("[client] socket() error.\n");
      return errno;
    }
  
  server.sin_family = AF_INET;
  server.sin_addr.s_addr = inet_addr(argv[1]);
  server.sin_port = htons (port);
    
  if (connect (sd, (struct sockaddr *) &server,sizeof (struct sockaddr)) == -1)
    {
      perror ("[client]connect() error.\n");
      return errno;
    }

  bzero (msg, 100);
  printf ("[client]Type a name: ");
  fflush (stdout);
  read (0, msg, 100);
    
  if (write (sd, msg, 100) <= 0)
    {
      perror ("[client]write() error to server.\n");
      return errno;
    }

  if (read (sd, msg, 100) < 0)
    {
      perror ("[client]read() error from server.\n");
      return errno;
    }

  printf ("[client]Received message is: %s\n", msg);

  close (sd);
}