C++语言程序设计（郑莉）第八章多态练习题

た入场券 2022-11-29 03:19 166阅读 0赞

**例1：定义一个哺乳动物Mammal类，再由此派生出狗Dog类，二者都定义 Speak()成员函数，基类中定义为虚函数，定义一个Dog类的对象，调用Speak函数，观察运行结果。**

#include <iostream>
    #include <string>
    using namespace std;
    
    class Mammel { 
    private:
    	string name;
    	int weight;
    public:
    	Mammel() { 
    		cout << "正在默认构造Mammel对象。" << endl;
    	}
    	Mammel(string name, int weight) { 
    		this->name = name;
    		this->weight = weight;
    	}
    	~Mammel();
    	virtual void speak();
    };
    void Mammel::speak() { 
    	cout << "Mammel" << endl;
    }
    Mammel::~Mammel() { 
    	cout << "正在析构Mammel对象。" << endl;
    }
    class Dog :public Mammel { 
    private:
    	int age;
    public:
    	Dog() { 
    		cout << "正在默认构造Dog对象。" << endl;
    	}
    	Dog(string name, int weight, int age);
    	~Dog();
    	void speak();
    };
    Dog::Dog(string name, int weight, int age) :Mammel(name, weight), age(age) { 
    	cout << "正在构造Dog对象。" << endl;
    }
    Dog::~Dog() { 
    	cout << "正在析构Dog对象。" << endl;
    }
    void Dog::speak() { 
    	cout << "Dog." << endl;
    }
    int main() { 
    	Dog mydog("haha", 20, 2);
    	mydog.speak();			//Dog
    	Mammel* animal1 = &mydog;
    	(*animal1).speak();		//Dog
    	Mammel& animal2 = mydog;
    	animal2.speak();			//Dog
    	Mammel animal3 = mydog;
    	animal3.speak();			//Mammel
    	//通过以上测试我们可以看出派生类转化为基类的三种方法：赋值、指针、引用
    	//只能通过指针，引用来访问虚函数
    
    	return 0;
    }

**例2：对类Point重载++（自增），-–（自减）运算符，要求同时重载前缀和后缀的形式。本答案也重载了‘+’， ‘-’， 实现连个点的加减。**

#include <iostream>
    using namespace std;
    
    class Point { 
    private:
    	int x, y;
    public:
    	Point(int xx = 0, int yy = 0) : x(xx), y(yy) { }
    	Point(const Point & p) : x(p.x), y(p.y) { }
    	~Point() { }
    	Point& operator++();
    	Point operator++(int);
    	Point& operator--();
    	Point operator--(int);
    	Point operator+(const Point& p2);
    	Point operator-(const Point& p2);
    	void ShowPoint() {  cout << "x: " << x << " y: " << y << endl; }
    };
    Point& Point::operator++() { 
    	x++;
    	y++;
    	return *this;
    }
    Point Point::operator++(int) { 
    	Point temp = *this;
    	++(*this);
    	return temp;
    	
    	//另一种写法，效果一样
    	/* int nx = this->x; int ny = this->y; ++(*this); return Point(nx, ny); */
    
    }
    Point& Point::operator--() { 
    	x--;
    	y--;
    	return *this;
    }
    Point Point::operator--(int) { 
    	Point temp = *this;
    	--(*this);
    	return temp;
    }
    Point Point::operator+(const Point& p2) { 
    	return Point(x + p2.x, y + p2.y);
    }
    Point Point::operator-(const Point& p2) { 
    	return Point(x - p2.x, y - p2.y);
    }
    
    int main() { 
    	cout << "后置加加：" << endl;
    	Point n1(2, 1);
    	n1.ShowPoint();
    	(n1++).ShowPoint();
    	n1.ShowPoint();
    
    	cout << endl << endl;
    	cout << "前置++：" << endl;
    	Point n2(3, 1);
    	n2.ShowPoint();
    	(++n2).ShowPoint();
    	n2.ShowPoint();
    
    	cout << endl << endl;
    	cout << "重载家减：" << endl;
    	Point n3(1, 1), n4(1, 1);
    	cout << "n5 = n3 + n4: " << endl;
    	Point n5 = n3 + n4;
    	n5.ShowPoint();
    	cout << "n6 = n3 - n4: " << endl;
    	Point n6 = n3 - n4;
    	n6.ShowPoint();
    
    	return 0;
    }

**例3：编写并测试一个计数器Counter类，对其重载运算符+。**

#include <iostream>
    using namespace std;
    class Counter { 
    private:
    	int a;
    public:
    	Counter() { }
    	Counter(int a):a(a){ }
    	~Counter(){ }
    	Counter operator+ (Counter& t);
    	void Show() {  cout << a << endl; }
    };
    Counter Counter::operator+ (Counter& t) { 
    	return Counter(a + t.a);
    }
    int main() { 
    	Counter a(1), b(2), c;
    	c = a + b;  //c.operator+(b)
    	c.Show();
    
    	return 0;
    }