#include <stdio.h>

const unsigned long bitPos[32] = {
   0x00000001, 0x00000002, 0x00000004, 0x00000008,
   0x00000010, 0x00000020, 0x00000040, 0x00000080,
   0x00000100, 0x00000200, 0x00000400, 0x00000800,
   0x00001000, 0x00002000, 0x00004000, 0x00008000,
   0x00010000, 0x00020000, 0x00040000, 0x00080000,
   0x00100000, 0x00200000, 0x00400000, 0x00800000,
   0x01000000, 0x02000000, 0x04000000, 0x08000000,
   0x10000000, 0x20000000, 0x40000000, 0x80000000
};

int multiplicity2 ( unsigned long n )
{
   int t = 0;

   if (n == 0) return -1;
   while ((n & 1) == 0) { ++t; n >>= 1; }
   return t;
}

unsigned long flipBit ( unsigned long code , int pos )
{
   if ((pos >= 0) && (pos <= 31)) {
      if (code & bitPos[pos])
         printf("Person %d leaves room, ", pos);
      else
         printf("Person %d enters room, ", pos);
      code ^= bitPos[pos];
   }
   return code;
}

void printBin ( unsigned long code , int s )
{
   int i;

   printf("code = ");
   for (i=s-1; i>=0; --i)
      if (code & bitPos[i]) printf("1"); else printf("0");
   printf(", Persons inside : ");
   for (i=s-1; i>=0; --i)
      if (code & bitPos[i]) printf("%d",i);
   printf("\n");
}

int main ()
{
   unsigned long code, i, k, s, t;

   printf("How many persons? "); scanf("%lu", &s);
   if (s == 0) {
      fprintf(stderr, "I expected a positive integer.\n");
      exit(1);
   }
   t = (1 << s);
   code = 0;
   printf("i =   0,                              ");
   printBin(code,s);
   for (i = 1; i < t; ++i) {
      printf("i = %3d, ", i);
      k = multiplicity2(i);
      printf("k = %d, ", k);
      code = flipBit(code,multiplicity2(i));
      printBin(code,s);
   }
   exit(0);
}