C++开闭原则实现：扩展开放，修改关闭

class Shape {
public:
    virtual ~Shape() = default;
    virtual double area() const = 0; // 纯虚函数
};

class Rectangle : public Shape {
    double width, height;
public:
    Rectangle(double w, double h) : width(w), height(h) {}
    double area() const override {
        return width * height;
    }
};
class Circle : public Shape {
double radius;
public:
Circle(double r) : radius(r) {}
double area() const override {
return 3.14159  radius  radius;
}
};

#include <iostream>
#include <vector>
void printAreas(const std::vector<Shape>& shapes) {
for (const auto s : shapes) {
std::cout << "Area: " << s->area() << "\n";
}
}
int main() {
std::vector<Shape*> shapes;
shapes.push_back(new Rectangle(4, 5));
shapes.push_back(new Circle(3));
printAreas(shapes);

// 清理资源
for (auto* s : shapes) {
    delete s;
}
return 0;
}