嘻唰唰第五批之三抽象基类

最新推荐文章于 2015-07-21 18:32:36 发布

原创最新推荐文章于 2015-07-21 18:32:36 发布 · 468 阅读

0 ·

CC 4.0 BY-SA版权

本文详细介绍了如何使用C++类模板和友元函数来实现不同几何形状（矩形、圆、三角形）的面积计算，并通过输入参数动态选择计算对象类型。重点展示了指针作为参数时的错误案例以及使用引用解决的方法。

问题及代码

#include <iostream>
#include<iomanip>
using namespace std;
class Shape
{
public:
    virtual void area() {}
};
class Rectangle:public Shape
{
    float a,b;
public:
    Rectangle(double i,double j):a(i),b(j) {}
    friend Shape printArea(Shape&p);
    void area()
    {
        cout<<a*b<<endl;
    }
};
class Circle:public Shape
{
    float r;
public:
    Circle(float i):r(i) {}
    friend Shape printArea(Shape&p);
    void area()
    {
        cout<<3.1415926*r*r<<endl;
    }
};
class Triangle:public Shape
{
    float w,h;
public:
    Triangle(double i,double j):w(i),h(j) {}
    friend Shape printArea(Shape&p);
    void area()
    {
        cout<<w*h/2<<endl;
    }
};
Shape printArea(Shape &p)
{
    p.area();
}
int main()
{
    float r,a,b,w,h;
    cout<<fixed<<setprecision(2);
    cin>>r;
    Circle circle(r);
    cout<<"area of circle = ";
    printArea(circle);
    cin>>a>>b;
    Rectangle rectangle(a,b);
    cout<<"area of rectangle = ";
    printArea(rectangle);
    cin>>w>>h;
    Triangle triangle(w,h);
    cout<<"area of triangle = ";
    printArea(triangle);
    return 0;
}