bla.cpp

#ifndef STRING
#define STRING
#include <string>
using namespace std;
#endif

#ifndef MEDIUM
#define MEDIUM
class Medium
 {
  public:
   string titel;
   bool ausleihstatus;
  
   virtual string getTyp() const =0;
 };
#endif

#ifndef CD
#define CD
class CD : public Medium
 {
  private:
   unsigned int spieldauer;
  public:
   string getTyp() const;
 };
#endif

string CD::getTyp()
 {
  return "CD";
 }