options using getopt in c

Question

I want the put a sub-option in a string so that I can use it as a file name for reading a file:

char *nvalue = NULL;
char *dvalue = NULL;
char *input = NULL;
char inputfilename[] = "\"";
int ar;

int main(int argc, char *argv[])
{
   while ((ar = getopt(argc, argv, "hn:d:i:")) != -1)
      switch (ar)
      {
         case 'h':
            printf("something");
            break; /* added */
         case 'n':
            nvalue = optarg;
            if (isdigit(nvalue))
               stop = atoi(nvalue);
            else
               printf("something\n");
            break; /* added */
         case 'd':
            dvalue = optarg;
            if (!strcmp(dvalue, "FCFS")   || !strcmp(dvalue, "SSTF") ||
                !strcmp(dvalue, "C-SCAN") || !strcmp(dvalue, "LOOK"))
               ;
            else
               printf("Invalid type of disk scheduling policy entered.\n");
            break; /* added */
         case 'i':
            input = optarg;
            strcpy(inputfilename, optarg);
            printf("Filename :%s\n", inputfilename);
            break;
      }
   /* ... */
}

So on the command line if I input:

./foobar -i hello

then I should be able to read the file with:

FILE *file = fopen(inputfilename, "r" );

any suggestions? answers? thanks!