https://media.cheggcdn.com/media/8c6/8c6d06da-aa61-4c53-9ff6-aeb760d1335d/php3yrHXa.png

#include <iostream>
#include <cmath>
#include <iomanip>

using namespace std;

double piValue() {
        double p = 1;
        int i = 1;

        while(true) {
                double prev = p;
                p += pow(-1, i) * (1.0 / (1 + 2*i));

                if(abs(prev - p) < 0.00005) {
                        break;
                }
                i++;
        }

        return 4*p;
}

int main() {
        cout << piValue() << endl;
}