题解 | #牛牛学圆#

使用面向对象思想

#include <iostream>
#include <iomanip>
#define PI 3.14159

using namespace std;

class Circle {
    public:
        Circle(double radius): _radius(radius){}
    
        // 计算周长
        double girth() {
            return _radius * 2 * PI;
        }
    
        // 计算面积
        double area() {
            return _radius * _radius * PI;
        }
    private:
        double _radius;
};


int main() {
    double radius;
    cin >> radius;
    
    Circle circle(radius);
    
    cout << fixed << setprecision(6) << circle.girth() << endl;
    cout << fixed << setprecision(6) << circle.area() << endl;
    
    return 0;
}