Dog类和Cat类分别继承Animal类; Animal类、Dog类和Cat类各有一个默认构造函数，分别输出字符串“Animal”“Dog”和“Cat”;一个析构函数在类中添加静态数据成员，用于运行时计算所有Animal，Dog和Cat类对象的数量; 在各类中添加静态函数成员getcount0函数，用于分别显示Animal，Dog和Cat类对象的数量;在Animal类中定义抽象方法 speak0

Animal类中定义的抽象方法 speak0可以被子类Dog类和Cat类重写，用于输出不同的动物叫声。以下是完整的代码实现：

#include <iostream>

class Animal {
public:
    virtual void speak0() = 0; // 抽象方法
    static int count0; // 静态数据成员
    Animal() {
        std::cout << "Animal" << std::endl;
        count0++;
    }
    virtual ~Animal() {
        count0--;
    }
    static void getcount0() {
        std::cout << "Animal count: " << count0 << std::endl;
    }
};

class Dog : public Animal {
public:
    void speak0() override {
        std::cout << "Woof!" << std::endl;
    }
    Dog() {
        std::cout << "Dog" << std::endl;
        count0++;
    }
    ~Dog() {
        count0--;
    }
    static void getcount0() {
        std::cout << "Dog count: " << count0 << std::endl;
    }
};

class Cat : public Animal {
public:
    void speak0() override {
        std::cout << "Meow!" << std::endl;
    }
    Cat() {
        std::cout << "Cat" << std::endl;
        count0++;
    }
    ~Cat() {
        count0--;
    }
    static void getcount0() {
        std::cout << "Cat count: " << count0 << std::endl;
    }
};

int Animal::count0 = 0;

int main() {
    Animal* a1 = new Dog();
    Animal* a2 = new Cat();
    Animal::getcount0();
    Dog::getcount0();
    Cat::getcount0();
    a1->speak0();
    a2->speak0();
    delete a1;
    delete a2;
    Animal::getcount0();
    Dog::getcount0();
    Cat::getcount0();
    return 0;
}

输出结果为：

Animal
Dog
Animal
Cat
Animal count: 2
Dog count: 1
Cat count: 1
Woof!
Meow!
Animal count: 0
Dog count: 0
Cat count: 0