/* client.c - code for example client program that uses TCP */#include <sys/socket.h>#include <sys/types.h>#include <netinet/in.h>#include <netdb.h>#include <stdio.h>#include <string.h>#include <stdlib.h>#include <unistd.h>#include <errno.h>int main(int argc, char *argv[]) {   struct  sockaddr_in sad; /* structure to hold an IP address     */  int     clientSocket;    /* socket descriptor                   */   struct  hostent  *ptrh;  /* pointer to a host table entry       */    char    *host;           /* pointer to host name                */  int     port;            /* protocol port number                */      char    Sentence[128];   char    modifiedSentence[128];   char    buff[128];  int     n;    if (argc != 3) {    fprintf(stderr,"Usage: %s server-name port-number\n",argv[0]);    exit(1);  }    /* Extract host-name from command-line argument */  host = argv[1];         /* if host argument specified   */    /* Extract port number  from command-line argument */  port = atoi(argv[2]);   /* convert to binary            */    /* Create a socket. */    clientSocket = socket(PF_INET, SOCK_STREAM, 0);  if (clientSocket < 0) {    fprintf(stderr, "socket creation failed\n");    exit(1);  }  /* Connect the socket to the specified server. */  memset((char *)&sad,0,sizeof(sad)); /* clear sockaddr structure */  sad.sin_family = AF_INET;           /* set family to Internet     */  sad.sin_port = htons((u_short)port);  ptrh = gethostbyname(host); /* Convert host name to equivalent IP address and copy to sad. */  if ( ((char *)ptrh) == NULL ) {    fprintf(stderr,"invalid host: %s\n", host);    exit(1);  }  memcpy(&sad.sin_addr, ptrh->h_addr, ptrh->h_length);    if (connect(clientSocket, (struct sockaddr *)&sad, sizeof(sad)) < 0) {    fprintf(stderr,"connect failed\n");    exit(1);  }    /* Read a sentence from user */    printf("Sentence   :   "); gets(Sentence);    /* Send the sentence to the server  */    write(clientSocket, Sentence, strlen(Sentence)+1);    /* Get the modified sentence from the server and write it to the screen*/  modifiedSentence[0]='\0';  n=read(clientSocket, buff, sizeof(buff));  while(n > 0){    strncat(modifiedSentence,buff,n);    if (buff[n-1]=='\0') break;    n=read(clientSocket, buff, sizeof(buff));  }    printf("Modified to -> %s\n",modifiedSentence);  /* Close the socket. */    close(clientSocket);  }