/*
 * https://rosettacode.org/wiki/100_doors#C
 */

#include <stdio.h>

int main()
{
  char is_open[101] = { 0 };
  int pass, door;

  /* do the 100 passes */
  for (pass = 1; pass <= 100; ++pass) {
    for (door = pass; door <= 100; door += pass) {
      is_open[door] = !is_open[door];
    }
  }

  /* output the result */
  for (door = 1; door <= 100; ++door) {
    printf("door #%3d is %s.\n", door, (is_open[door]? "open" : "closed"));
  }

  return 0;
}