This program calculates the permutation:

using namespace System;

long Factorial(long number)
{
	if( number <= 1 )
		return 1;
	else
		return number * Factorial(number - 1);
}

long Permutation(long n, long r)
{
	if( r == 0 )
		return 0;
	if( n == 0 )
		return 0;
	if( (r >= 0) && (r <= n) )
		return Factorial(n) / Factorial(n - r);
	else
		return 0;
}

int main()
{
	Console::WriteLine(L"F(10) = {0}\n",
		Factorial(10));
	Console::WriteLine(L"F(6) = {0}\n",
		Factorial(6));
	Console::WriteLine(L"P(10, 4) = {0}\n",
		Permutation(10, 4));

	return 0;
}

This would produce:

F(10) = 3628800

F(6) = 720

P(10, 4) = 5040

Press any key to continue . . .