dont understandhow to use select in udpserver

Hello all experts,
 i am unable to use select in my udpserver program that sends string "sendtext" to clients and clients (udpclient.c)back to server.
        Please help me to make following program as UDPSERVER which is actually TCPSERVER program with select call used.

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

#define LOCAL_SERVER_PORT 9200

int main()
{
    int server_sockfd, client_sockfd;
    int server_len, client_len;
    struct sockaddr_in server_address;
    struct sockaddr_in client_address;
    int result;
    fd_set readfds, testfds;
    unsigned char msg[1024],recvtext[1024],sendtext[1024];
    struct timeval timeout;
    strcpy(sendtext,"mystring");


    server_sockfd = socket(AF_INET, SOCK_DGRAM, 0);

    server_address.sin_family = AF_INET;
    server_address.sin_addr.s_addr = htonl(INADDR_ANY);
    server_address.sin_port = htons(1500);
    server_len = sizeof(server_address);

    bind(server_sockfd, (struct sockaddr *)&server_address, server_len);


    listen(server_sockfd, 5);

    FD_ZERO(&readfds);
    FD_SET(server_sockfd, &readfds);


    while(1) {
       
        int fd;
        int nread;
        int  rc, n;
        timeout.tv_sec = 5;
        timeout.tv_usec = 000000;

        testfds = readfds;

        printf("server waiting\n");
        result = select(FD_SETSIZE, &testfds, (fd_set *)0,
            (fd_set *)0, &timeout);

        if(result < 1) {
            perror("server5");
            exit(1);
        }


        for(fd = 0; fd < FD_SETSIZE; fd++) {
            if(FD_ISSET(fd,&testfds)) {


                if(fd == server_sockfd) {
                    client_len = sizeof(client_address);
                    client_sockfd = accept(server_sockfd,
                        (struct sockaddr *)&client_address, &client_len);
                    FD_SET(client_sockfd, &readfds);
                    printf("adding client on fd %d\n", client_sockfd);
                }

                else {
                    ioctl(fd, FIONREAD, &nread);

                    if(nread == 0) {
                        close(fd);
                        FD_CLR(fd, &readfds);
                        printf("removing client on fd %d\n", fd);
                    }

                    else {
      sendagain:
rc = sendto(fd,sendtext, strlen(sendtext)+1, 0,(struct sockaddr *) &server_address, sizeof(server_address));

if(rc<0) {
printf("cannot send data \n");
close(fd);
exit(1);
}
memset(msg,0x0,1024);
client_len = sizeof(client_address);
n = recvfrom(fd, recvtext, 1024, 0, (struct sockaddr *) &client_address, &client_len);
if(strcmp(senttext,recvtext)!=0)
goto sendagain;
                    }
                }
            }
        }
    }
}