（1）定义猫科动物Animal类，包含虚函数 Sound( )。由其派生出猫类（Cat）和豹类（Leopard）。在main函数中定义Animal类的指针指向派生类的对象并调用Sound（）函数实现多

#include<iostream>
using namespace std;
class Animal
{
public:
virtual void sound()
{
cout<<"animal speak!"<<endl;
}
};
class Cat:public Animal
{
public: 
virtual void sound()
{
cout<<"cat speak!"<<endl;
}
};
class Leopard:public Animal
{
public:
virtual void sound()
{
cout<<"leopard speak!"<<endl;
}
};
int main()
{
Animal *a;
Cat c1;
a=&c1;
a->sound();
Leopard l;
a=&l;
a->sound();
return 0;

}