/* calculates all subsets of the string comb by assigning eatch letter a position in a binary number and counting up. */
#include <stdio.h>
#include <string.h>

// #define DEBUG

int main() {
  char* comb = "ABCD";
  int count = strlen(comb);
  // that bitshifting is the same is squaring count
  int permutations = (1 << count);

  printf("string is %s\nthere are %d permutations", comb, permutations);

  for (unsigned char i = 0; i < permutations; i++) {
    for (unsigned char j = 0; j < 4; j++) {
      // when j=0, will result in 0b0001, when j=1, 0b0010, j=2 0b0100.
      unsigned char mask = 1 << j;
#ifdef DEBUG
      printf(" j=%x mask=%x, postmask=%x, i=%x", j, mask, (i & mask), i);
#endif /* ifdef DEBUG */
      if ((i & mask) != 0) {
        printf(" %c", comb[j]);
      }
    }
    printf("\n");
  }

  return 0;
}