【问题描述】 定义一个图形类(figure),其中有保护类型的成员数据：高度(height)和宽度(width)，一个公有的构造函数。由该图形类建立两个派生类：矩形类(rectangle)和等腰三角形类(triangle)。在每个派生类中都包含一个函数area（），分别用来计算矩形和等腰三角形的面积. 还有display()函数,显示对象的信息. 主函数如下: int main() { double width,height; cin>>width>>height; triangle tri(width,height); rectangle rect(width,height); tri.display(); cout<<"The area is "<<tri.area()<<endl; rect.display(); cout<<"The area is "<<rect.area()<<endl; return 0; } 【输入形式】宽度和高度 【输出形式】主函数输出，注意标点、空格 按主函数输出 【样例输入】3 4 【样例输出】 I am a triangle. The value of width is 3, the height is 4.The area is 6 I am a rectangle. The value of width is 3, the height is 4.The area is 12 【样例说明】 【评分标准】

以下是具体实现，其中要注意调用基类的构造函数来初始化高度和宽度：

#include <iostream>
using namespace std;

class figure {
protected:
    double height;
    double width;
public:
    figure(double h, double w): height(h), width(w) {}
    virtual double area() = 0;
    virtual void display() = 0;
};

class rectangle: public figure {
public:
    rectangle(double h, double w): figure(h, w) {}
    double area() {
        return height * width; 
    }
    void display() {
        cout << "I am a rectangle. The value of width is " << width << ", the height is " << height << ".";
    }
};

class triangle: public figure {
public:
    triangle(double h, double w): figure(h, w) {}
    double area() {
        return height * width / 2;
    }
    void display() {
        cout << "I am a triangle. The value of width is " << width << ", the height is " << height << ".";
    }
};

int main() {
    double width, height;
    cin >> width >> height;
    triangle tri(width, height);
    rectangle rect(width, height);
    tri.display();
    cout << " The area is " << tri.area() << endl;
    rect.display();
    cout << " The area is " << rect.area() << endl;
    return 0;
}