#include <iostream>
#include <iomanip>   //for setw and setprecision
#include <cstdlib>
using namespace std;

int main()
{
	double sum {0.0};         //gets closer and closer to pi
	double sign {1.0};        //alternates between 1.0 and -1.0
	double denominator {1.0}; //grows by 2.0 during each loop

	for (int i {1}; i <= 1000; ++i) {
		//means sum = sum + sign * 4.0 / denominator 
		sum += sign * 4.0 / denominator;

		cout << setw(4) << i << "   "   //3 spaces between the columns
			<< fixed << setprecision(5) << sum << "\n";

		sign = -sign;
		denominator += 2.0;   //means denominator = denominator + 2.0
	}

	return EXIT_SUCCESS;
}