[Constants]

Constants.cpp

namespace Constants
{

    // actual global variables

    extern const double pi(3.14159);

    extern const double avogadro(6.0221413e23);

    extern const double my_gravity(9.2); // m/s^2 -- gravity is light on this planet

}

Constants.h

#ifndef CONSTANTS_H

#define CONSTANTS_H

namespace Constants

{

    // forward declarations only

    extern const double pi;

    extern const double avogadro;

    extern const double my_gravity;

}

#endif