#include <stdio.h>
#include "Boolean.h"
#include "combinatorics.h"

/* For all the functions below, return TRUE if the
   calculation is successful, FALSE if overflow occurs
   Return the calculated value in the pass by reference
   parameter provided
*/

Boolean calcFactorial (int n, int* nfact)
{
    *nfact = 1;

	while(n > 0)
	{
	       *nfact = *nfact * n;
		   n--;	   
	}

	if(*nfact < 0x7fffffff)
	{
		return TRUE;
	}
	else
	{
		return FALSE;
	}
}

/*
Combination means C(n,r) = n!/( r! * (n-r)! ) 
where C(n,r) is the number of r-element subsets of an n-element set.
Better formula derived from above is:
          n ( n-1 ) ( n-2 ) ... ( n-r+1 ) 
 C(n,r) = ------------------------------- 
          r ( r-1 ) ( r-2 ) ... (3)(2)(1) 


  Return True if calculation is successful. False if
  Overflow occurs.
*/

Boolean calcCNR( int n, int r, int* cnr )
{
                       //#define min(n,r) = (((n) < (r)) ? (n) : (r));

    int answer = *cnr;
	int multiplier;
	int divisor = 1;
	int k;

	if(n < r)
	{
		k = n;
	}
	else
	{
		k = r;
	}

	while(divisor <= k)
	{
			answer = (answer * multiplier) / divisor;
	
		    multiplier--;
		    divisor++;
	}
}

Boolean calcCNR( int n, int r, int* cnr )
{
    #define min(n,r)  (((n) < (r)) ? (n) : (r));

    int answer = *cnr;
	int multiplier;
	int divisor = 1;
	int k;
   
	/*
	if(n < r)
	{
		k = n;
	}
	else
	{
		k = r;
	}
	*/

	k = min(r,n-r);
    answer = 1;
	while(divisor <= k)
	{
		    

			answer = (answer * multiplier) / divisor;
	
		    multiplier--;
		    divisor++;
	}
}


void main()
{
   int result;
	int n;
	int r;

	printf("Input two number:  ");
	scanf("%d %d", &n, &r);

	calcCNR(n, r, &result);

	printf("result of cnr is: %d\n", result);
}