[redhead]

If you don't want to run into a buffer problem, you need to turn towards something like dynamic memory allocation with the use of malloc()...
Now I don't want to provide you with the actual program, but in this case I would advice you to split it up, say create a seperate function, where you've actualy create the file ie:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

/* predefine the file-creation function, so we know it exist, 
 * when refferencing to it from main() 
 */
int create_file(char* filename, int count);

int main(int argc, char* argv[])
{
  /* this is the main function in my example with getopt()
   * in this one every instance of:
   * for(j=1; j < count; ++j)
   *   printf("Creating file: ...");
   * is exchanged with:
   * create_file(argv[i], count);
   */
}


/* this is the actual body of the create_file(), 
 * This will create a files by the name: filename-n
 * for n in {1, 2, ..., count}
 */

int create_file(char* filename, int count)
{
  char* buff; /* our filename with dynamic memory allocation */
  /* how long will our char* need to be */
  int length = strlen(filename)+3; /* add room for '-' and '\0' */ 
  int i,n=count;
  /* deside length */
  while(n >= 10){
    length++;
    n=n/10;
  }
  /* allocate needed memory for filename-count */
  if(!(buff = (char*) malloc(sizeof(char*)*length)))
    return -1; /* error allocating memory */
  for(i=1; i <= count; ++i){
    snprintf(buff, length, "%s-%d", filename, i);
    if(!access(buff, F_OK))
      printf("Error file: %s exist\n", buff);
    else
      printf("Creating file: %s\n", buff);
  }
  free(buff); /* make sure we dont hogg unneeded memory */
  return 0;
}

I hope I didn't provide you with too much help.. Since I like for you to figure out how this thing actualy should work by yourself..

Naturaly I could have said..

malloc() is used in a way like:

#include <stdio.h>
#include <stdlib.h>

int main()
{
  char* buff;
  int length=1337;
  if(!(buff = (char*) malloc(sizeof(char*)*length))){
    printf("Error allocating memory on the heap\n");
    return -1;
  }
  else
    printf("Success in allocating memory on the heap\n");
  free(buff);
  return 0;
}

And then tell you to figure out how to use it in your program...
But then again, I wouldn't be encurraging you to make a reasonable design in your program, so you wont end up with a main() function which is thousands of lines long...

But as an exercise I've left the part of combining the example for getopt() with this small example...