man select

 
int keep_running = TRUE;
int socket;
int c;
char buffer[BUF_SIZ];
 
// Open socket and set O_NONBLOCK flag.
 
while (keep_running)
{
    while (true)
    {
        if ((c = getch())!=ERR)  // there was a char from the terminal read.
            break;
        usleep(100);
        errno = 0;
        if (recv(socket, buffer, sizeof(buffer), MSG_WAITALL)!=-1 && 
            (errno==EAGAIN || errno==EWOULDBLOCK)  // received bytes from socket.
            break;
    }
    if (c==ERR)  // No terminal char so buffer must have bytes from socket
    {
         // Process socket buffer.
    }
    else  // read char from terminal.
    {
        // Process terminal char.
    }
}

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

#include <ncurses.h>

#define MAXDATASIZE 1024
#define STDIN 0

int main(int argc, char *argv[]) {

        int sockfd, nbytes, c, keep_running = TRUE;
        char sbuf[MAXDATASIZE];
        char rbuf[MAXDATASIZE];
        struct hostent *he;
        struct sockaddr_in their_addr;
        fd_set read_fds;

        if (argc < 2 || argc > 4) {
                fprintf(stderr, "usage: client <hostname> [port] [nickname]\n");
                exit(1);
        }

        int port = 3067;
        if (argc > 2) {
                port = atoi(argv[2]);
                printf("using port %i\n", port);
        } else
                printf("using default port %i\n", port);

        initscr();
        //noecho();
        cbreak();
        nodelay(stdscr, TRUE);
        keypad(stdscr, TRUE);
        printw("Press F9 to quit\n");
        refresh();

        if ((he = gethostbyname(argv[1])) == NULL) {
                herror("gethostbyname");
                exit(1);
        }

        // set flags
        int flags = fcntl(sockfd, F_GETFL);
        flags |= O_NONBLOCK;
        fcntl(sockfd, F_SETFL, flags);

        if ((sockfd = socket(PF_INET, SOCK_STREAM, 0)) == -1) {
                perror("socket");
                exit(1);
        }

        their_addr.sin_family = AF_INET;
        their_addr.sin_port = htons(port);
        their_addr.sin_addr = *((struct in_addr *)he->h_addr);
        memset(&(their_addr.sin_zero), '\0', 8);

        if (connect(sockfd, (struct sockaddr *)&their_addr, sizeof(struct sockaddr)) == -1) {
                perror("socket");
                exit(1);
        }

        while (keep_running) {
                while (true) {
                        if ((c = getch()) != ERR)
                                break;
                        usleep(100);
                        errno = 0;
                        if (recv(sockfd, rbuf, sizeof(rbuf), MSG_WAITALL) != -1 && 
(errno == EAGAIN || errno == EWOULDBLOCK))
                                break;
                }
                if (c == ERR) {
                        printf("Message from you: %c (%i)\n", c, c);
                        if (c == 19)
                                keep_running = FALSE;
                }
                else {
                        printf("Message from server: %s\n", rbuf);
                }
        }

        printf("quitting time.. hit any key to continue\n");
        nodelay(stdscr, FALSE);
        getch();
        endwin();
        close(sockfd);
        return 0;
}