Unbinding ports - c

Question

I launched a process from terminal that bound some ports.
The code in questions is this one:
#include <sys/socket.h>
#include <sys/un.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#define BUF_SIZE 500
#define LISTEN_BACKLOG 50
#define handle_error(msg) \
do { perror(msg); exit(EXIT_FAILURE); } while (0)
int
main(int argc, char *argv[])
{
struct addrinfo hints;
struct addrinfo *res, *rp;
struct sockaddr_storage peer_addr;
socklen_t peer_addr_len;
int sfd, cfd;
if(argc != 3) {
fprintf(stderr, "Usage: %s address port\n", argv[0]);
exit(EXIT_FAILURE);
}
memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE;
hints.ai_protocol = 0;
hints.ai_addr = NULL;
hints.ai_next = NULL;
if(getaddrinfo(argv[1], argv[2], &hints, &res) != 0)
handle_error("getaddrinfo");
// Try each socket until we bind
for(rp = res; rp != NULL; rp = rp->ai_next){
sfd = socket(rp->ai_family, rp->ai_socktype, 0);
if(sfd == -1) continue;
if(bind(sfd, rp->ai_addr, rp->ai_addrlen) == 0) break;
else close(sfd);
}
freeaddrinfo(res);
if (rp == NULL){
fprintf(stderr, "Could not bind to any socket\n");
exit(EXIT_FAILURE);
}
// Set the TCP socket to listen state
if (listen(sfd, LISTEN_BACKLOG) == -1) handle_error("listen");
printf("Server started");
for(;;){
// Accept
peer_addr_len = sizeof(struct sockaddr_storage);
cfd = accept(sfd, (struct sockaddr *) &peer_addr, &peer_addr_len);
if (cfd == -1) handle_error("accept");
// Fork
pid_t pid = fork();
if (pid == 0){ //Child code
pid_t my_pid = getpid();
char buf[BUF_SIZE];
while(1){
ssize_t nread = recv(cfd, buf, BUF_SIZE, 0);
if (nread == 0) {
close(cfd);
exit(EXIT_SUCCESS);
} else {
buf[nread] = 0;
fprintf(stdout, "Worker %i has received a message: %s", my_pid, buf);
ssize_t nsent = send(cfd, buf, nread, 0);
if (nsent != nread) fprintf(stderr, "Error sending response");
}
}
}
close(sfd);
}
After invoking the code I killed the process, and noticed that I could not run the program twice using the same port.
I checked sudo lsof -i -P -n | grep LISTEN and it listed the ports I had used for testing as being in LISTEN state and my program being the culprit for that.
How can I unbind the ports? How do I modify my code so it unbinds the ports itself after receiving a suitable signal?