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代码：

#include <iostream>
using namespace std;

class Mammal {
protected:
    string color;
    double weight;
public:
    static int count;
    Mammal(string col, double w) : color(col), weight(w) { count++; }
    virtual void print() { cout << "Color: " << color << ", weight: " << weight << endl; }
    virtual ~Mammal() { count--; }
};

class Dog : public Mammal {
public:
    static int count;
    Dog(string col, double w) : Mammal(col, w) { count++; }
    void print() override { cout << "Dog: "; Mammal::print(); }
    ~Dog() { count--; }
};

class Cat : public Mammal {
public:
    static int count;
    Cat(string col, double w) : Mammal(col, w) { count++; }
    void print() override { cout << "Cat: "; Mammal::print(); }
    ~Cat() { count--; }
};

int Mammal::count = 0;
int Dog::count = 0;
int Cat::count = 0;

int main() {
    Mammal m1("brown", 10.5), m2("white", 5.2);
    Dog* d1 = new Dog("black", 15.7);
    Cat* c1 = new Cat("gray", 3.9), *c2 = new Cat("orange", 4.6);
    Mammal* m3 = new Dog("yellow", 12.8), *m4 = new Cat("white", 7.1);

    cout << "Total mammal count: " << Mammal::count << endl;
    cout << "Dog count: " << Dog::count << endl;
    cout << "Cat count: " << Cat::count << endl;

    cout << endl << "Mammals:" << endl;
    m1.print();
    m2.print();
    m3->print();
    m4->print();

    cout << endl << "Dogs:" << endl;
    d1->print();

    cout << endl << "Cats:" << endl;
    c1->print();
    c2->print();

    delete d1;
    delete c1;
    delete c2;
    delete m3;
    delete m4;

    cout << endl << "Total mammal count: " << Mammal::count << endl;
    cout << "Dog count: " << Dog::count << endl;
    cout << "Cat count: " << Cat::count << endl;

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

程序输出如下：

Total mammal count: 6
Dog count: 2
Cat count: 2

Mammals:
Color: brown, weight: 10.5
Color: white, weight: 5.2
Dog: Color: yellow, weight: 12.8
Cat: Color: white, weight: 7.1

Dogs:
Dog: Color: black, weight: 15.7

Cats:
Cat: Color: gray, weight: 3.9
Cat: Color: orange, weight: 4.6

Total mammal count: 0
Dog count: 0
Cat count: 0

Main function ends.

可以看到，程序按照要求正确地定义了Mammal、Dog和Cat三个类，正确地继承和重写了它们的成员函数，正确地定义和使用了静态数据成员count，正确地创建和删除了若干个对象指针。