How do I clear the stdin in C? - c

Question

In a multi-client/server implementation I am connecting the client and server and then taking inputs from the client's stdin to send to server (otherwise if there's an incoming message from the server, I am performing a recv() and I am using select() to switch between the two). Now, as an example, I am giving an input "LOGIN IP PORT" and that connects me to the server. And then I am back to the client's command line again.
NOW, when I am back at the command line again after the login command, if I press enter without typing any specific command, the previous LOGIN command is executed again, it seems. I think the stdin is not being flushed. Although I have done fseek(stdin,0,SEEK_END), it's still not getting flushed. The client side main loop code is as below:
while(TRUE) {
fd_max = server_fd;
FD_ZERO(&sock_list);
FD_SET(STDIN, &sock_list);
FD_SET(server_fd, &sock_list);
printf("\n[PA1-Client]$ ");
fflush(stdout);
fseek(stdin,0,SEEK_END);
selret = select(fd_max + 1, &sock_list, NULL, NULL, NULL);
if(selret < 0)
perror("Select failed");
else {
int sock_index;
for(sock_index = 0; sock_index<=fd_max; sock_index++) {
if(FD_ISSET(sock_index, &sock_list)) {
if(sock_index == STDIN) {
char* cmd = (char*) malloc(sizeof(char)*CMD_SIZE);
if(fgets(cmd, CMD_SIZE - 1, stdin) == NULL)
exit(-1);
cmd[strcspn(cmd, "\n")] = '\0'; char* token[3];
tokenize(cmd, token, " ");
if(!strcmp(token[0], "LOGIN")) {
server_fd = clientLogin(token[1], token[2]);
}
else if(!strcmp(token[0], "REFRESH")) {
clientRefresh(token[0]);
}
else if(!strcmp(token[0], "LOGOUT")) {
clientLogout(token[0]);
}
else if(!strcmp(token[0], "EXIT")) {
clientExit(token[0]);
exit(0);
}
else if(!strcmp(token[0], "SEND")) {
clientSend(cmd);
}
else if(!strcmp(token[0], "BROADCAST")) {
clientBroadcast(cmd);
}
else if(!strcmp(token[0], "BLOCK")) {
clientBlock(cmd);
}
else if(!strcmp(token[0], "UNBLOCK")) {
clientUnblock(cmd);
}
else if(!strcmp(token[0], "AUTHOR")) {
commonAuthor();
}
else if(!strcmp(token[0], "IP")) {
commonIP();
}
else if(!strcmp(token[0], "PORT")) {
commonPort();
}
else if(!strcmp(token[0], "LIST")) {
commonList();
}
}
else {
char* buffer = (char*)malloc(sizeof(char)*MSG_SIZE);
if(recv(server_fd, buffer, sizeof(buffer), 0) == 0) {
close(server_fd);
server_fd = 0;
}
else
msgRecvEvent(buffer);
}
}
}
}
}
return 0;
}