56纯虚函数与抽象类

#include <iostream>
using namespace std;
 
// 抽象类 Shape
class Shape {
public:
    virtual double area() = 0; // 纯虚函数
};
 
// 派生类 Rectangle
class Rectangle: public Shape {
public:
    double width;
    double height;
    Rectangle(double w, double h): width(w), height(h) {}
    double area() override { return width * height; } // 重写虚函数
};
 
// 派生类 Circle
class Circle: public Shape {
public:
    double radius;
    Circle(double r): radius(r) {}
    double area() override { return 3.14 * radius * radius; } // 重写虚函数
};