封装一个名为Shape（图形）的父类，从父类中派生两个子类，分别为Circle（圆形），Rect（矩形），父类拥有两个子类的共同特性，面积和周长，两个子类除了继承父类的共性，还需封装各自的成员属性

类的声明

#ifndef SHAPE_H
#define SHAPE_H

class Shape
{
protected:
    double per;
    double area;

public:
    Shape():per(0),area(0) {}
    Shape(double per, double area);
    Shape(const Shape& obj);

    ~Shape() {}
};


class Circle : public Shape
{
private:
    double radius;

public:
    Circle():Shape(0, 0), radius(0) {}
    Circle(double radius);
    Circle(const Circle& obj);

    double& Get_Per();
    double& Get_Area();

    ~Circle() {}
};

class Rect : public Shape
{
private:
    double length;
    double width;

public:
    Rect():Shape(0, 0), length(0), width(0) {}
    Rect(double length, double width);
    Rect(const Rect &obj);

    double& Get_Per();
    double& Get_Area();

    ~Rect() {}
};

#endif // SHAPE_H

类的实现

#include "Shape.h"

Shape::Shape(double per, double area):per(0), area(0)
{
    this->per = per;
    this->area = area;
}

Shape::Shape(const Shape& obj)
{
    per = obj.per;
    area = obj.area;
}


Circle::Circle(double radius):Shape(0, 0), radius(0)
{
    this->radius = radius;
}

Circle::Circle(const Circle& obj)
{
    radius = obj.radius;
    per = obj.per;
    area = obj.area;
}

double& Circle::Get_Per()
{
    per = 2*3.14*radius;

    return per;
}

double& Circle::Get_Area()
{
    area = 3.14 * radius * radius;

    return area;
}


Rect::Rect(double length, double width):Shape(0, 0), length(0), width(0)
{
    this->length = length;
    this->width = width;
}

Rect::Rect(const Rect &obj)
{
    length = obj.length;
    width = obj.width;
    per = obj.per;
    area = obj.area;
}

double& Rect::Get_Per()
{
    per = 2 * (length + width);

    return per;
}

double& Rect::Get_Area()
{
    area = length * width;

    return area;
}

最终的效果图