近似计算

计算：π/4=1-1/3+1/5-1/7+…,直到最后一项小于10^-6

#include<iostream>
using namespace std;

int main()
{
    double sum = 0, per;
    int i=1;
    do
    {
        per = 1.0/(2*i-1);
        if(i%2 == 1)
        {
            sum += per;
        }
        else 
        {
            sum -= per;
        }
        i++;
    }
    while(per >= 1e-6);
    cout << sum;
    return 0;
}