西电机试练习-编写程序求π

#include<bits/stdc++.h>

using namespace std;

double arctan(double x)
{
    
    
    double sqr = x * x;
    double e = x;
    double r = 0;
    int i = 1;
    while(e / i > 1e-15)
    {
    
    
        double f = e / i;
        r = (i % 4 == 1) ? r + f : r - f;
        e = e * sqr;
        i = i + 2;
    }
    return r;
}

int main()
{
    
    
    double a = 16.0 * arctan(1 / 5.0);
    double b = 4.0 * arctan(1 / 239.0);
    cout<<"PI = "<<a - b<<endl;
    return 0;
}