pi / 2 = 1 + 1/3 + 1/3 * 2/5 + 1/3 * 2/5*3/7+ 1/3 * 2/5*3/7*4/9+......

// JiShuPI.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

#include <IOSTREAM>
#include <CSTDIO>
#include <CSTDLIB>

using namespace std;

double JiShuPI()
{
	double PI = 2,tmep = 2;
	int n = 1,m = 3;

	while(tmep > 1e-15)
	{
		tmep = tmep * n / m;
		PI += tmep;
		n++;
		m+=2;
	}
	return PI;	
}


int main(int argc, char* argv[])
{
	double PI;
	PI = JiShuPI();
	printf("PI = %f\n", PI);

	return 0;
}