实现：抽象类和多态的实例

示例代码如下：

#include<iostream>
#include<string>

using namespace std;

class Animal {
public:

	virtual void speak() = 0;
};

class Dog :public Animal{
public:
	void speak() {
		cout << "小狗在说话" << endl;
	}
};

class Cat :public Animal {
public:
	void speak() {
		cout << "小猫在说话" << endl;
	}
};

void aaa(Animal * animal) {
	animal->speak(); //因为是指针，所以我们调用的时候使用->
	delete animal; //用完之后释放内存
}

void test01() {
	Animal * a1 = new Cat;
	aaa(a1);
}

int main() {
	test01();
	system("pause");
	return 0;
}