#include <iostream.h>
#include <math.h>
//This is under construction.
void input(int& number, int& number_out_of);
void combine(int number, int number_out_of);
void permut(int number, int number_out_of);
long factorial(int argument);


void main()
{
	int x, y;
	char ans, go_on;

	cout << "WARNING: This program cannot handle numbers larger than\n";
	cout << "12 due to the huge size of factorials.\n";

	do{
	cout << "Permutations(p) or combinations(c)? -->";
	cin >> ans;

	switch(ans)
	{
	case 'c':
	case 'C':
		input(x,y);
		combine(x,y);
		break;
	case 'p':
	case 'P':
		input(x,y);
		permut(x,y);
		break;
	default:
		cout << "Invalid response.\n";
	}

	cout <<"\nDo it again?(y/n) -->";
	cin >> go_on;
	}while(go_on == 'y' || go_on == 'Y');

	return;
}

void input(int& number, int& number_out_of)
{
	cout << "Input number of slots: -->";
	cin >> number_out_of;
	cout << "Input number of objects: -->";
	cin >> number;
	if(number_out_of > number || number_out_of <= 0 || number <= 0)
	{
		cout << "Try again.\n";
		input(number, number_out_of);
	}
	return;
}

void combine(int number, int number_out_of)
{
	long x, y, z, answer;

	x = factorial(number);
	y = factorial(number_out_of);
	z = factorial(number - number_out_of);

	answer = x/(y*z);

	cout << "\nThere are " << answer << " combinations.\n";
	return;
}

void permut(int number, int number_out_of)
{
	long x, y, answer;
	
	x = factorial(number);
	y = factorial(number - number_out_of);

	answer = x/y;

	cout << "\nThere are " << answer << " permutations.\n";
	return;
}

long factorial(int argument)
{
	long product = 1;
	while(argument > 0)
	{
		product = argument * product;
		argument--;
	}

	return product;
}