C++计算PI的值

#include <iostream>

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 += 2;

          }

          return r;

}

主程序

int main() {

          double a = 16.0 * arctan(1/5.0);

          double b = 4.0 * arctan(1/239.0);

          //注意：因为整数相除结果取整，如果参数写1/5，1/239，结果就都是0

 

          cout << "PI = " << a - b << endl;

          return 0;

}