新手 C++用arctan求pai的问题

[再见孙俉空]

#include<iostream>
#include<cmath>
using namespace std;
double arctan(double);
int main()
{
cout << 16 * arctan(1.0 / 5) - 4 * arctan(1.0 / 239) << endl;

system("pause");
return 0;
}
double arctan(double x)
{
int sum = 0;
int k = 1;
for (int i = 1; pow(x, i) / i > 1e-15; i += 2)
{
sum += (k*pow(x, i) / i);
k = -k;
}
return sum;
}



输出是0，自己实在找不出哪里错了，求大神指点

[sdghchj]

double sum = 0;

double sum = 0;