#include <stdio.h>
#include <gsl/gsl_combination.h>

int main (void) 
{
    gsl_combination * c;
    size_t i;

    printf("All subsets of {0,1,2,3} by size:\n") ;
    for(i = 0; i <= 4; i++)
    {
      c = gsl_combination_calloc (4, i);
      do {
          printf("{");
          gsl_combination_fprintf (stdout, c, " %u");
	  gsl_combination_valid(c); // added this check
            printf(" }\n");
         }
      while (gsl_combination_next(c) == GSL_SUCCESS);
      gsl_combination_free(c);
    }

    return 0;
}