/* server.c - code for example server 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 server's address  */  int     port;            /* protocol port number                */    struct  sockaddr_in cad; /* structure to hold client's address  */  int     alen;            /* length of address                   */    int     welcomeSocket, connectionSocket; /* socket descriptors  */    char    clientSentence[128];   char    capitalizedSentence[128];   char    buff[128];  int     i, n;    /* Check command-line argument for protocol port and extract   */  /* port number if one is specified. Otherwise, give error      */  if (argc > 1) {                /* if argument specified        */    port = atoi(argv[1]);        /* convert argument to binary   */  } else {     fprintf(stderr,"Usage: %s port-number\n",argv[0]);    exit(1);  }    /* Create a socket */  welcomeSocket = socket(PF_INET, SOCK_STREAM, 0); /* CREATE SOCKET */  if (welcomeSocket < 0) {    fprintf(stderr, "socket creation failed\n");    exit(1);  }    /* Bind a local address to the socket */    memset((char *)&sad,0,sizeof(sad)); /* clear sockaddr structure   */  sad.sin_family = AF_INET;           /* set family to Internet     */  sad.sin_addr.s_addr = INADDR_ANY;   /* set the local IP address   */  sad.sin_port = htons((u_short)port);/* set the port number        */     if (bind(welcomeSocket, (struct sockaddr *)&sad, sizeof(sad)) < 0) {    fprintf(stderr,"bind failed\n");    exit(1);  }    /* Specify the size of request queue */    if (listen(welcomeSocket, 10) < 0) {    fprintf(stderr,"listen failed\n");    exit(1);  }    /* Main server loop - accept and handle requests */    while (1) {    alen = sizeof(cad);    if ( (connectionSocket=accept(welcomeSocket, (struct sockaddr *)&cad, &alen)) < 0) {      fprintf(stderr, "accept failed\n");      exit(1);    }        /* Get the sentence from the client */        clientSentence[0]='\0';    n=read(connectionSocket,buff,sizeof(buff));    while(n > 0){      strncat(clientSentence,buff,n);      if (buff[n-1]=='\0') break;      n=read(connectionSocket,buff,sizeof(buff));    }        /* Capitalize the sentence */        for(i=0; i <= strlen(clientSentence); i++){      if((clientSentence[i] >= 'a') && (clientSentence[i] <= 'z'))	capitalizedSentence[i] = clientSentence[i] + ('A' - 'a');      else	capitalizedSentence[i] = clientSentence[i];    }        /* send it to the client */        write(connectionSocket, capitalizedSentence, strlen(capitalizedSentence)+1);        close(connectionSocket);  }}