反手就是一个类

#include <bits/stdc++.h>
using namespace std;
const double PI=3.14159;
class Circle{
	public:
		double r;
	public:
		double D()
		{
			return 2*r;
		}
		double S()
		{
			return PI*r*r;
		}
		double C()
		{
			return 2*r*PI;
		} 
};
int main()
{
	Circle cir;
	cin>>cir.r;
	cout<<fixed<<setprecision(4)<<cir.D()<<" "<<cir.C()<<" "<<cir.S()<<endl;	
	return 0;
}