4/17c++练习打卡

#include<iostream>
using namespace std;

class Counter {
    friend Counter& operator +(const Counter& a, const Counter& b);
    int num;
public:
    Counter() { num = 0; }
    Counter(int num_) :num(num_){}
    
    //Counter operator +(const Counter& a)
    //{
    //    Counter res;
    //    res.num = num += a.num;
    //    return res;
    //}

    int display()
    {
        return num;
    }
};

Counter& operator +(const Counter& a,const Counter& b)
{
    Counter* res = new Counter;
    res->num = a.num + b.num;
    return *res;
}

void test()
{
    Counter a(5);
    Counter b(4);

    Counter c = a + b;
    Counter d = c + a + b;
    cout << "c的值是：" << c.display() << "      d的值是：" << d.display() << endl;

}

int main()
{
    test();
    return 0;
}
 
8-5
class Mammal {
public:
    virtual void speak()
    {
        cout << "哺乳动物说话。。。" << endl;
    }
};

class Dog :public Mammal {
public:
    void speak()
    {
        cout << "狗狗说话。。。" << endl;
    }
};

int main()
{
    Dog a;
    a.speak();
    return 0;
}
 
8-6
class Shape {
public:
    virtual double getarea()
    {
        return 0;
    }
    virtual double getperim() {
        return 0;
    }
};

class Rectangle :public Shape {
public:
    Rectangle(double c, double d) :a(c), b(d) {}
    double getarea()
    {
        return a * b;
    }
    double getperim() {
        return 2 * (a + b);
    }

private:
    double a;
    double b;
};

class Circle :public Shape {
public:
    Circle(double a) :r(a) {}
    double getarea()
    {
        return 3.14 * r * r;
    }
    double getperim() {
        return 2 * 3.14 * r;
    }
private:
    double r;
};

void test02() {
    Rectangle a1(5, 4);
    Circle a2(5);

    cout << a1.getarea() << endl;
    cout << a2.getarea() << endl;
    cout << a1.getperim() << endl;
    cout << a2.getperim() << endl;
}

int main()
{
    test02();
    return 0;
}
8-7
class Point {
    friend void test();
    double x;
    double y;
public:
    Point(){}
    Point(double a, double b) :x(a), y(b) {}

    Point& operator ++ () {
        x++;
        y++;
        return *this;
    }

    Point operator ++(int) {
        Point tmp;
        tmp.x = x;
        tmp.y = y;
        x++;
        y++;
        return tmp;
    }
};

void test()
{
    Point a(5, 6);
    ++(++a);
    cout << a.x << "," << a.y << endl;
    cout << (a++).x << endl;
    cout << a.x << endl;
}

int main()
{
    test();
    return 0;
}