多态性10

#include<iostream>
using namespace std;
class Mammal{
public:
virtual void speak() const=0;
};
class Dog:public Mammal{
public:
virtual void speak() const override{
cout<<"Dog is speaking!"<<endl;
}
};
int main()
{
Dog dog;
Mammal *p;
dog.speak();
p=&dog;

p->speak();
return 0;
}