#include <iostream>
const double PI = 3.14159;
class Circle
{
 private:
 double r;

 public:
 Circle(double r_)
 {
 r = r_;
 }
 double area()
 {
 return PI * r * r;
 }
 double perimiter()
 {
 return 2 * PI * r;
 }
};
int main()
{
 double r;
 std::cout << "请输入圆的半径:";
 std::cin >> r;
 Circle c = Circle(r);
 std::cout << "圆的面积为:" << c.area() << std::endl;
 std::cout << "圆的周长为:" << c.perimiter() << std::endl;
}