// Self contained implementation in a class
#include <iostream>
#include <cmath>
using namespace std;

class Planet{
  public:
    void SetMassRadius(double mass, double radius){
      M = mass;
      R = radius;
      G = 6.67428e-11;
    }
    double Density(){ return 1.0e-3 * M/(4.0*M_PI*R*R*R/3); }
    double Gravity(){ return G*M/(R*R); }
  private:
    double M, R, G;
};

int main(){
   Planet Mars;

   Mars.SetMassRadius(6.4e23, 3.4e6);

   cout << "Density = " << Mars.Density() << endl;
   cout << "Gravity = " << Mars.Gravity() << endl;
}