C++代码，用精确的PI求解

解题思路: Π = arccos(-1) = 2arcsin(1) = 4arctan(1)

注意事项:需要引入C头文件<cmanth>

参考代码:

#include <iostream>

#include <cstdio>

#include <cmath>

#define PI acos(-1)//acos(-1)为PI的精确值，头文件是math.h 

using namespace std;

int main(){

    double num(0);

double area(0);

    cin >> num;

    area = PI * pow(num,2);//PI*num^2

    printf("%.2lf",area);

return 0;

}