1  
   2  #include <stdio.h>
   3  
   4  /* Print n as a binary number */
   5  void printbitssimple(int n) {
   6  	unsigned int i;
   7  	i = 1<<(sizeof(n) * 8 - 1);
   8  
   9  	while (i > 0) {
  10  		if (n & i)
  11  			printf("1");
  12  		else
  13  			printf("0");
  14  		i >>= 1;
  15  	}
  16  }
  17  
  18  /* Print n as a binary number */
  19  void printbits(int n) {
  20  	unsigned int i, step;
  21  
  22  	if (0 == n) { /* For simplicity's sake, I treat 0 as a special case*/
  23  		printf("0000");
  24  		return;
  25  	}
  26  
  27  	i = 1<<(sizeof(n) * 8 - 1);
  28  
  29  	step = -1; /* Only print the relevant digits */
  30  	step >>= 4; /* In groups of 4 */
  31  	while (step >= n) {
  32  		i >>= 4;
  33  		step >>= 4;
  34  	}
  35  
  36  	/* At this point, i is the smallest power of two larger or equal to n */
  37  	while (i > 0) {
  38  		if (n & i)
  39  			printf("1");
  40  		else
  41  			printf("0");
  42  		i >>= 1;
  43  	}
  44  }
  45  
  46  int main(int argc, char *argv[]) {
  47  	int i;
  48  	for (i = 0; i < 16; ++i) {
  49  		printf("%d = ", i);
  50  		printbitssimple(i);
  51  		printf("\n");
  52  	}
  53  
  54  	return 0;
  55  }
  56  

   1  
   2  #include <stdio.h>
   3  
   4  /* Applies the mask to a set like {1, 2, ..., n} and prints it */
   5  void printv(int mask[], int n) {
   6  	int i;
   7  	printf("{ ");
   8  	for (i = 0; i < n; ++i)
   9  		if (mask[i])
  10  			printf("%d ", i + 1); /*i+1 is part of the subset*/
  11  	printf("\b }\n");
  12  }
  13  
  14  /* Generates the next mask*/
  15  int next(int mask[], int n) {
  16  	int i;
  17  	for (i = 0; (i < n) && mask[i]; ++i)
  18  		mask[i] = 0;
  19  
  20  	if (i < n) {
  21  		mask[i] = 1;
  22  		return 1;
  23  	}
  24  	return 0;
  25  }
  26  
  27  int main(int argc, char *argv[]) {
  28  	int n = 3;
  29  
  30  	int mask[16]; /* Guess what this is */
  31  	int i;
  32  	for (i = 0; i < n; ++i)
  33  		mask[i] = 0;
  34  
  35  	/* Print the first set */
  36  	printv(mask, n);
  37  
  38  	/* Print all the others */
  39  	while (next(mask, n))
  40  		printv(mask, n);
  41  
  42  	return 0;
  43  }