声明一个Shape抽象类,在此基础上派生出矩形Rectangle和圆Circle类,二者都有GetArea( )函数计算对象的面积,GetPerim( )函数计算对象的周长。完成类的设计,其中PI取3.14159。 主程序如下(不能修改): int main() {

以下是Shape抽象类以及Rectangle和Circle类的设计：

#include <iostream>

using namespace std;

const double PI = 3.14159;

class Shape {
public:
    virtual double GetArea() = 0;
    virtual double GetPerim() = 0;
};

class Rectangle : public Shape {
public:
    Rectangle(double l, double w) : length(l), width(w) {}
    double GetArea() override {
        return length * width;
    }
    double GetPerim() override {
        return 2 * (length + width);
    }
private:
    double length;
    double width;
};

class Circle : public Shape {
public:
    Circle(double r) : radius(r) {}
    double GetArea() override {
        return PI * radius * radius;
    }
    double GetPerim() override {
        return 2 * PI * radius;
    }
private:
    double radius;
};

在主程序中，我们可以使用指向基类对象的指针，来调用不同派生类对象的同名函数，从而实现多态。

int main() {
    Shape* shape1 = new Rectangle(3, 4);
    cout << "Rectangle area: " << shape1->GetArea() << endl;
    cout << "Rectangle perimeter: " << shape1->GetPerim() << endl;
    delete shape1;

    Shape* shape2 = new Circle(5);
    cout << "Circle area: " << shape2->GetArea() << endl;
    cout << "Circle perimeter: " << shape2->GetPerim() << endl;
    delete shape2;

    return 0;
}