C++基础01

//公式求π//π=16arctan(1/5)-4arctan(1/239)//arctan(x)公式arctan(x)=x/1-x*x*x/3+x*x*x*x*x/5+...=∑(-1)的n次方*x的2n+1次方/2n+1#include<iostream>using namespace std;int main(){double a,b;double arctan(double x);a=16.0*arctan(1/5.0);b=4.0*arctan(1/239.0);cout<<"PI="<<a-b<<endl;return 0;}double arctan(double x){int i;double r,e,f,sqr;sqr=x*x;r=0;e=x;i=1;while(e/i>1e-15){f=e/i;r=(i%4==1)?r+f:r-f;e=e*sqr;i+=2;}return r;}