How to compare data sent by client in server C programing

I want to send a option from the client to a server. The server have to do some comparisons and send a string back to the client. I can receive the data from the client, but my server crashes in the moment of comparison (it gets to the else with the "error input" and ends the connection). Can someone tell me what I'm doing wrong?

Incorrect Inputclose error: Bad file descriptor

Program exited with code 01.

Server:

void
result(int sockfd)
{
    ssize_t     n;
    char        buf[MAXLINE];
    int         temp;
    time_t      ticks;
again:
    while ((n =read(sockfd, buf, MAXLINE)> 0))
    {
     temp = rand() % 22;
     if (buf=="A\n" || buf=="a\n")
     {
      snprintf(buf, sizeof(buf), "You option is number is -%i, time is %.24s\r\n", temp,ctime(&ticks));
      Writen(sockfd, buf, n);
     }
     if (buf=="B\n" || buf=="f\")
     {
      snprintf(buf, sizeof(buf), "You option is number is -%i, time is %.24s\r\n", temp,ctime(&ticks));
      Writen(sockfd, buf, n);
     }
     else
     {
       printf("Incorrect Input");
       Close(sockfd);
     }  
    }
    if (n < 0 && errno == EINTR)
    goto again;
    else if (n < 0)
        err_sys("read error");
}

int
main(int argc, char **argv)
{
    int         listenfd, connfd;
    socklen_t       len;
    struct sockaddr_in  servaddr, cliaddr;
    char            buff[MAXLINE];
        char            recvline[MAXLINE + 1];

    listenfd = Socket(AF_INET, SOCK_STREAM, 0);
    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family      = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);/*----------------------------------------------------*/
    servaddr.sin_port        = htons(5678); 

    Bind(listenfd, (SA *) &servaddr, sizeof(servaddr));
    Listen(listenfd, LISTENQ);
    printf("EDMTS is running on 129.128.4.80, listening on port 5678\n");
    printf("\n");
    printf("Waiting for incoming connections...Press Ctrl+C to end server\n");

    for ( ; ; )
         {
        len = sizeof(cliaddr);
        connfd = Accept(listenfd, (SA *) &cliaddr, &len);

        /*Client connects to server*/
        printf("\n");
        printf("Connection from %s, port %d\n",
               Inet_ntop(AF_INET, &cliaddr.sin_addr, buff, sizeof(buff)),
               ntohs(cliaddr.sin_port));

                result(connfd);
                Close(connfd);
        printf("Conexion cerrada...Esperando siguiente cliente\n");
        }
}

Client

void
get_temp(FILE *fp, int sock)
{
    char    sendline[MAXLINE], recvline[MAXLINE];

    while (Fgets(sendline, MAXLINE, fp) != NULL) {

        Writen(sock, sendline, strlen(sendline));

        if (Readline(sock, recvline, MAXLINE) == 0)
            err_quit("Server Terminated Prematurely");

        Fputs(recvline, stdout);
    }
}


int
main(int argc, char **argv)
{
    int                 sockfd, n;
    socklen_t           len;
    char                recvline[MAXLINE + 1];
    struct sockaddr_in  servaddr, cliaddr;
    char  scale[2];

    if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
        err_sys("socket error");

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port   = htons(atoi(argv[2])); 
    if (inet_pton(AF_INET, argv[1], &servaddr.sin_addr) <= 0) 
        err_quit("inet_pton error for %s", argv[1]);

    printf("Connect...\n");
    if (connect(sockfd, (SA *) &servaddr, sizeof(servaddr)) < 0)
        err_sys("connect error");

    len = sizeof(cliaddr);
    Getsockname(sockfd, (SA *) &cliaddr, &len);
    printf("Local Address is: %s\n",
           Sock_ntop((SA *) &cliaddr, sizeof(cliaddr))); 

    printf("Enter option A or B): ");
    get_temp(stdin, sockfd);

    exit(0);
}

When I run the debugger to find out my variables, I find:

Breakpoint 1, result (sockfd=7) at servertest.c:236 236
printf("Random es %i\n",temp); (gdb) p buf $1 = "A\n", '\0' , "\203\217��", '\0' , "h\206��h\206��\204\210��#��\000\000\000\000�\206��߷\020\207��#��", '\0' , "��\000\000\000\000\000\000\000\000�\017��", '\0' , "h\206��", '\0' , "\001\000\000\000\000\000\000\000�\207��", '\0' , "��\t\000\000\000#��\030��\000\000\000\000h\206��\003", '\0' , "\n\000\000\000g\206��", '\0' , " "... (gdb) p temp $2 = 17

Thank you very much

Solution

First of all, you can't compare C strings using == (you will compare pointer adresses, and the address of buf[0] and the address of your static string "a\n" will certainly not be equal. To compare the strings, use strncmp().

Your crash happens because after you call Close(), the read() function is called again on the socket file descriptor. To remove the crash, put a break; after the Close(), like so:

else
 {
   printf("Incorrect Input");
   Close(sockfd);
   break;
 }