client.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>

void error(const char *msg) {
    perror(msg);
    exit(0);
}

int main(int argc, char *argv[]) {
    int sockfd;//socket file descriptor
    ssize_t n; // for storing returned value from client
    uint16_t portno;
    struct sockaddr_in serv_addr;//contains sin_family, sin_port, struct  in_addr sin_addr, sin_zero[8]
    struct hostent *server;
    /*
    struct hostent {
    char *h_name;       // official name of host 
    char **h_aliases;   // alias list 
    int h_addrtype;     // host address type 
    int h_length;       // length of address 
    char **h_addr_list; // list of addresses 
    };  
    */

    char buffer[256]; // for storing message returned from client side
    if (argc < 3) {
        fprintf(stderr,"usage %s hostname port\n", argv[0]);
        exit(0);
    }
    portno = (uint16_t)atoi(argv[2]);
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
        error("ERROR opening socket");
    server = gethostbyname(argv[1]);//this returned your computer host name
    if (server == NULL) { // in case you entered wrong host
        fprintf(stderr,"ERROR, no such host\n");
        exit(0);
    }
    
    bzero((char *) &serv_addr, sizeof(serv_addr));//The bzero() function shall place n zero-valued bytes in the area pointed to by s.
    serv_addr.sin_family = AF_INET;
    bcopy(server->h_addr, //official name of host
          (char *)&serv_addr.sin_addr.s_addr,//contains ip address
          (size_t)server->h_length);//length of address 
    serv_addr.sin_port = htons(portno);//function converts the unsigned short integer hostshort from host byte order to network byte order. 
    
    if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
        error("ERROR connecting");
    printf("Please enter the message: ");
    bzero(buffer,256);
    fgets(buffer,255,stdin);
    n = write(sockfd,buffer,strlen(buffer));
    if (n < 0)
        error("ERROR writing to socket");
    bzero(buffer,256);
    n = read(sockfd,buffer,255);
    if (n < 0)
        error("ERROR reading from socket");
    printf("%s\n",buffer);
    close(sockfd);
    return 0;
}