Implementation: abstract classes and examples of polymorphic

Sample code is as follows:

#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;
}