写出下列程序的运行结果 #include class In

#include<iostream.h>
class Instrument{
public:
virtual void display()const{cout<<"Instrument::display"<<endl;}
};
class Piano:public Instrument{
public:
void display()const{cout<<"Piano::display"<<endl;}
};
class Guitar:public Instrument{
public:
void display()const{cout<<"Guitar::display"<<endl;}
};
void tone(Instrument & i)
{i.display();}
void main(void){
Guitar guitarl;
tone(guitarl)
Piano pianol;
tone(piano1);
}