Find DNS names given Subnet Mask and Network Address

#include <netdb.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <string.h>
#include <stddef.h>
 
int main(int argcount, char* argvector[])
{
   if(argcount <= 1)
   {
      printf("\n\nThe usage for this program is \"listDNS (target subnet id)\".\n");
      printf("\n   Example: listDNS 165.95.5.0\n\n");
      return 0;
   }
   
   struct hostent *hostPtr;
   char* ip_addr_dot;
   char ip_addr_tmp[16];
   struct in_addr *addrPtr;
   u_long ip_addr_long;
   u_long ip_addr_long_nl;
 
   //parse argument (ip address) to ip_addr_dot
   ip_addr_dot = argvector[1];
 
   //determine last octet in ip address
   strcpy(ip_addr_tmp, ip_addr_dot );
   const char delimiters[] = ".";
   char *token;
   token = strtok( ip_addr_tmp, delimiters );
   token = strtok( NULL, delimiters );
   token = strtok( NULL, delimiters );
   token = strtok( NULL, delimiters );
  
   if( token == NULL )
   {
       printf("Error: the ip address you have provided is not valid!\n"); 
       return 0;
   }
   
   //convert last octet into an integer
   int lastOctet = atoi(token);
 
   //convert ip address string into long integer
   ip_addr_long = inet_addr(ip_addr_dot);
 
   while( lastOctet < 255 )
   {
     //convert to long and increment ip address
     ip_addr_long_nl = htonl(ip_addr_long);  //outputs 0.10.95.165          
     ip_addr_long_nl++;                      //increments to 1.10.95.165     
     ip_addr_long = htonl(ip_addr_long_nl);  //converts back to 165.95.10.1  
 
     addrPtr = (struct in_addr *) &ip_addr_long;
 
     hostPtr = gethostbyaddr(addrPtr, 4, AF_INET);
     if( hostPtr != NULL )
     {
        // Display IP addresses
        while(*(hostPtr->h_addr_list) != NULL)
        {      
          addrPtr = (struct in_addr *) *hostPtr->h_addr_list;
          printf("%s", inet_ntoa(*addrPtr));
          hostPtr->h_addr_list ++;
        }
 
        // Display Hostname
        printf(": %s",  hostPtr->h_name);
 
        while(*(hostPtr->h_aliases) != NULL)
        {
          printf(", %s", *(hostPtr->h_aliases)); 
          hostPtr->h_aliases++;
        }
 
        // Display new line
        printf("\n");
 
     }
     lastOctet++;
   }
 
   return 0;
}
                                              

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