Aggregation and composition

[crueltyfree]

Hi! I'm learning composition and aggregation and I've got some problems with the latter. Here is my code

  #include <iostream>
#include <locale>
using namespace std;
class Polygon {
    protected:
	float moneyperhour, hours;
	public:
  	void set_values(float a, float b){
  		hours=a; moneyperhour=b;
	  }	
};
class Driver: public Polygon {
	private:
	string number = "äåñÿòü";
	public: 
	float salary(){return ((hours*moneyperhour)*20)/100;}
	string GetNumber(){
		return number;
	}
};
class TouristicCoach: public Polygon { 
    public:
    float cost () {return (hours*moneyperhour);}
    void seat()
    {
    	passenger.seat();
	}
	void Info(){
	     cout<<"\n"<<" àâòîï³äïðèºìñò³ º "<<driver.GetNumber()<<" âî䳿â"<<endl;
	}
	private:
    class Passenger{
    	private:
    		int seats[4]={19,38,56,82};
    	public:
    		void seat(){
    		cout<<"Ìàêñèìàëüíà ê³ëüê³ñòü ïàñàæèð³â ì³êðîàâòîáóñà "<<seats[0]<<"."<<endl;
			cout<<"Ìàêñèìàëüíà ê³ëüê³ñòü ïàñàæèð³â íåâåëèêîãî àâòîáóñà "<<seats[1]<<"."<<endl;
			cout<<"Ìàêñèìàëüíà ê³ëüê³ñòü ïàñàæèð³â ñåðåäíüîãî àâòîáóñà "<<seats[2]<<"."<<endl;
			cout<<"Ìàêñèìàëüíà ê³ëüê³ñòü ïàñàæèð³â âåëèêîãî àâòîáóñà "<<seats[3]<<"."<<endl;	
			}	
	};
	Passenger passenger;
	static Driver driver;
};
int main () {
   SetConsoleCP(1251);
   SetConsoleOutputCP(1251);
   TouristicCoach passengers;
   passengers.seat();
   TouristicCoach drivers;
   drivers.Info();
   cout<<"\n"<<"Ââåä³òü ïîòð³áíó ê³ëüê³ñòü ãîäèí."<<endl;
   float hour;
   cin>>hour;
    TouristicCoach minibus;
	minibus.set_values(hour,200);
    cout<<"Çà îðåíäó ì³êðîàâòîáóñà íà "<<hour<<" ãîäèí ïîòð³áíî ñïëàòèòè "<< minibus.cost()<<" ãðèâåíü." << endl; 
	TouristicCoach small;
	small.set_values(hour,400);
    cout<<"Çà îðåíäó íåâåëèêîãî àâòîáóñà íà "<<hour<<" ãîäèí ïîòð³áíî ñïëàòèòè "<< small.cost()<<" ãðèâåíü." << endl;
    TouristicCoach medium;
	medium.set_values(hour,600);
    cout<<"Çà îðåíäó ñåðåäíüîãî àâòîáóñà íà "<<hour<<" ãîäèí ïîòð³áíî ñïëàòèòè "<<medium.cost()<<" ãðèâåíü."<< endl;
    TouristicCoach big;
	big.set_values(hour,800);
    cout<<"Çà îðåíäó âåëèêîãî àâòîáóñà íà "<<hour<<" ãîäèí ïîòð³áíî ñïëàòèòè "<<big.cost()<<" ãðèâåíü." << endl;
    Driver minidriver;
    minidriver.set_values(hour,200);
    Driver smalldriver;
    smalldriver.set_values(hour,400);
    Driver medidriver;
    medidriver.set_values(hour,600);
    Driver bigdriver;
    bigdriver.set_values(hour,800);
    cout<<"\n"<<"Çà ïåðåâåçåííÿ ì³êðîàâòîáóñîì âîä³é îòðèìຠ"<<minidriver.salary()<<" ãðèâåíü."<<endl;
    cout<<"Çà ïåðåâåçåííÿ íåâåëèêì àâòîáóñîì âîä³é îòðèìຠ"<<smalldriver.salary()<<" ãðèâåíü."<<endl;
    cout<<"Çà ïåðåâåçåííÿ ñåðåäí³ì àâòîáóñîì âîä³é îòðèìຠ"<<medidriver.salary()<<" ãðèâåíü."<<endl;
    cout<<"Çà ïåðåâåçåííÿ âåëèêèì àâòîáóñîì âîä³é îòðèìຠ"<<bigdriver.salary()<<" ãðèâåíü."<<endl;
    return 0;
}
  

The compiler message is
undefined reference to 'TourisricCoach::driver'
ld returned 1 exit status
I guess there is a problem with void Info function.
I would appreciate any help.
Thank you in advance!

[Ganado]

The problem is driver is a static class member, so it traditionally needs to be defined outside the class definition itself (or with the inline keyword starting in C++17).
https://stackoverflow.com/questions/5019856/initialize-static-variables-in-c-class

It's not clear why you even need your static Driver driver; variable to be static. Why not just make it Driver driver; and initialize it in your TouristicCoach constructor?

Also please note that variable names like 'a' and 'b' are usually inappropriate because they tell me nothing about what that variable represents.

[crueltyfree]

Yes, you are right, Ganado! It wasn't a good isea to make it static. Without static my ptogram works correctly. Thank you very much!