#include <iostream>
#include <cmath>

using namespace std;

class Kreis {
  public:
    static constexpr double pi = acos(-1.0);

  private:
    double r;

  public:
    Kreis(double r_ = 1): r(r_) {}
    double radius() { return r; }
    double umfang() { return 2*r*pi; }

    static double flaeche(Kreis k) {
      return pi*k.r*k.r;
    }
    double zylinder(double h) {
      return h * flaeche(*this);
    }
};

int main() {
  Kreis k{0.5};
  cout << "Radius:       " << k.radius() << endl
       << "Umfang:       " << k.umfang() << endl
       << "Flaeche:      " << Kreis::flaeche(k) << endl
       << "Zylindervol.: " << k.zylinder(2) << endl;

  return 0;
}