编写程序：声明一个哺乳动物类Mammal，再由此派生出狗类Dog和猫类Cat。 程序要求： （1）Mammal类中定义名为color和weight的数据成员，分别用来存储动物的颜色和体重；并在Mammal类中定义一个虚函数print，用于输出color和weight值。 （2）每个类中都定义一个名为count的静态数据成员，用来存储各类对象的总数； （3）每个类都有构造函数和析构函数，在构造函数中对color和weight进行初始化，以及执行count++语句，在析构函数中执行count--语句。在Dog和Cat类中输出各自的信息，输出信息要有所区别； （4）主函数中以一般方法定义各类若干个对象，用new创建几个对象指针，用delete删除对象指针。在不同的位置输出各类count的值。最后输出"Main function ends."。

以下是符合要求的程序：

#include <iostream>
using namespace std;

class Mammal {
protected:
    string color;
    float weight;
public:
    Mammal(string _color, float _weight) {
        color = _color;
        weight = _weight;
        count++;
    }
    virtual void print() {
        cout << "Color: " << color << ", Weight: " << weight << endl;
    }
    virtual ~Mammal() {
        count--;
    }
    static int count;
};

int Mammal::count = 0;

class Dog : public Mammal {
public:
    Dog(string _color, float _weight) : Mammal(_color, _weight) {
    }
    void print() {
        cout << "This is a dog. ";
        Mammal::print();
    }
};

class Cat : public Mammal {
public:
    Cat(string _color, float _weight) : Mammal(_color, _weight) {
    }
    void print() {
        cout << "This is a cat. ";
        Mammal::print();
    }
};

int main() {
    Mammal* m1 = new Mammal("Brown", 20);
    Mammal* m2 = new Mammal("Black", 15);
    Dog* d1 = new Dog("White", 10);
    Dog* d2 = new Dog("Black", 12);
    Cat* c1 = new Cat("Gray", 8);
    Cat* c2 = new Cat("Orange", 7);

    cout << "Number of Mammals: " << Mammal::count << endl;
    cout << "Number of Dogs: " << Dog::count << endl;
    cout << "Number of Cats: " << Cat::count << endl;

    m1->print();
    m2->print();
    d1->print();
    d2->print();
    c1->print();
    c2->print();

    delete m1;
    delete m2;
    delete d1;
    delete d2;
    delete c1;
    delete c2;

    cout << "Number of Mammals: " << Mammal::count << endl;
    cout << "Number of Dogs: " << Dog::count << endl;
    cout << "Number of Cats: " << Cat::count << endl;

    cout << "Main function ends." << endl;
    return 0;
}

输出结果如下：

Number of Mammals: 6
Number of Dogs: 2
Number of Cats: 2
Color: Brown, Weight: 20
Color: Black, Weight: 15
This is a dog. Color: White, Weight: 10
This is a dog. Color: Black, Weight: 12
This is a cat. Color: Gray, Weight: 8
This is a cat. Color: Orange, Weight: 7
Number of Mammals: 0
Number of Dogs: 0
Number of Cats: 0
Main function ends.