// without the compiler commands, f & g infinitely
// call each other.  
// Try removing the 
// #ifndef #define and #endif from g.h and f.h
// and see what happens.
#ifndef _F_H_
#define _F_H_
#include "g.h"
void f();

namespace universal{

class rocket{
private:
   int thrust;
public:
   rocket():thrust(0){}
   rocket(int t):thrust(t){}
   int getThrust() const;
   void setThrust(int );
};

}
#endif