Trouble with PI approximation

Question

I'm trying to simulate the approximation of pi to 5 decimal places. This is the formula off of which I'm basing it:

But instead of using infinity, I'm approximating it to 5 decimals. This is the code I have, but the result I get is 0. My speculation is because of the integer division, but I've tried adding 0. to one of the dividens but it doesn't help:

#include <cmath>
#include <iostream>

int main() {

    int sum = 0;

    for (int k = 0; k < 5; ++k) {

        sum += pow(-1, k) / (2 * k + 1);

    }

    sum *= 4;

    std::cout << sum;

}

This part:

sum += pow(-1, k) / (2 * k + 1);

I tried changing to:

sum += ( pow(-1, k) + 0. ) / (2 * k + 1);

or

sum += ( pow(-1, k) * 1. ) / (2 * k + 1);

But the result is still 0. What could I be doing wrong?

Answer 1

You have to declare sum as double.