combinatorics algorithms

#include <stdio.h>
#define N 5
#define M 3
 
char str[N+1];
char dig[10] = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};
int counter;
char used[N];
 
//generate binary strings
void bstrings(int k)
{
  if (k==-1)
  {
    printf("%s\n", str);
    return;
  }
  str[N-1-k] = '0'; bstrings(k-1);
  str[N-1-k] = '1'; bstrings(k-1);
}
 
 
//generate all possible strings of length N on M digits 
void strings(int k)
{
  int i;
 
  if (k==-1)
  {
	  //do something with the string
	  printf("%d. %s\n", ++counter, str);
	  return;
  }
 
  for(i=0; i<M; i++)
  {
    str[N-k-1] = dig[i]; 
    strings(k-1);
  }
}
 
//generate all permutations on N digits
void permstrings(int k)
{	
	int i;
 
	if (k==-1)
	{
		printf("%d. %s\n", ++counter, str);
		return;
	}
 
	for(i=0; i<N; i++)
	{
		//do something with the string
		if (!used[i])
		{
		  str[N-k-1] = dig[i];
		  used[i] = 1;
		  permstrings(k-1);
		  used[i] = 0;
		}
	}
}
 
 
 
int _tmain(int argc, _TCHAR* argv[])
{
	permstrings(N-1);
	getchar();
	return 0;
}