[YTU]_2477( C++习题 抽象基类)

题目描述

编写一个程序，声明抽象基类Shape，由它派生出3个派生类： Circle(圆形)、Rectangle(矩形)、Triangle(三角形)，用一个函数printArea分别输出以上三者的面积（结果保留两位小数），3个图形的数据在定义对象时给定。

输入

圆的半径
矩形的边长
三角形的底与高

输出

圆的面积
矩形的面积
三角形的面积

样例输入

12.6
4.5 8.4
4.5 8.4

样例输出

area of circle = 498.76
area of rectangle = 37.80
area of triangle = 18.90
#include <iostream>
#include <iomanip>
using namespace std;
class Shape
{
public:
    virtual float area()=0;
};
class Circle:public Shape
{
public:
    Circle(float r):radius(r){}
    float area() {return radius*radius*3.1415926;}
private:
    float radius;
};
 
class Rectangle:public Shape
{
public:
    Rectangle(float a1,float b1):chang(a1),kuan(b1){}
    float area(){return chang*kuan;}
private:
    float chang,kuan;
};
 
class Triangle:public Shape
{
public:
    Triangle(float d,float g):di(d),gao(g){}
    float area(){return di*gao*0.5;}
private:
    float di,gao;
};
void printArea(Shape &s)
{
    cout<<s.area()<<endl;
}
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;
}