Создать класс в C++

struct Machine{
   friend class Mechanic;
   friend Machine& riding(Machine& car);
   friend bool operator>(const Machine& lhs, const Machine& rhs);
 
   struct Motor{
   };
   static const string& get_model() const{
      return model;
   }
private :
   double durability;
   static const string model;
};
 
Machine& riding(Machine& car){
   car.durability -= 0.5; 
   return car;
}
 
struct Mechanic{
   Machine& repair(Machine& car){
      car.durability =100.;
      return car;
   }
};

class Car;
class Mechanic;
class Engine;
 
class Engine
{
};
 
 
class Car
{
public:
    Car()
        : carName(""), condition(100){}
    Car(std::string _CarName, int _condition)
        : carName(_CarName), condition(_condition)
    {
        if (condition > 100)
            condition = 100;
    }
    friend void trip(Car& car);
    friend bool operator >(const Car& a, const Car& b);
    friend Mechanic;
private:
    std::string carName;
    unsigned int condition;     // 0 - 100%
 
};
 
bool operator >(const Car& a, const Car& b)
{
    return a.condition > b.condition ? 1 : 0;
}
void trip(Car& car)     // every trip - 10% 
{
    if (car.condition - 10 <= 0)
    {
        std::cout << "The car is broken\n";
        return;
    }
    car.condition -= 10;
}
 
class Mechanic
{
public:
    void repair(Car& car) { car.condition = 100;}
    static std::string modelAuto;
    static std::string getModel() { return modelAuto; }
    Engine a;
};
 
std::string Mechanic::modelAuto{"ZAZ"};
 
int main()
{   
    Mechanic meh;
    
    std::cout<<Mechanic::getModel()<<std::endl;
    Car a("car1", 100);
    Car b("car2", 200);
    bool val = a>b;
    std::cout <<  val << std::endl;
    trip(b);
    val = a > b;
    std::cout << val << std::endl;
return 0;