虚函数-计算图形面积

Problem B: C++习题 虚函数-计算图形面积

Description

编写一个程序，定义抽象基类Shape，由它派生出5个派生类： Circle(圆形)、Square(正方形)、Rectangle(矩形)、Trapezoid(梯形)、Triangle(三角形)。

用虚函数分别计算几种图形面积，并求它们之和。

要求用基类指针数组，使它每一个元素指向一个派生类对象。

Input

圆的半径

正方形的边长

矩形的边长

梯形的上底和下底，高

三角形的底与高

Output

所有图形面积之和（结果保留两位小数）

Sample Input

12.6
3.5
4.5 8.4
2.0 4.5 3.2
4.5 8.4

Sample Output

total of all areas=574.11

HINT

#include <iostream>
#include <iomanip>
using namespace std;
class Shape
{
public:
    virtual double area() const=0;
}; 

class Circle:public Shape
{
public:
Circle(double r):radius(r){}
virtual double area() const{return 3.14159*radius*radius;}
protected:
    double radius;
}; 

class Rectangle:public Shape
{
public:
Rectangle(double r,double l):width(r),height(l){}
virtual double area() const{return width*height;}
protected:
    double width;
    double height;
}; 

class Triangle:public Shape
{
public:
Triangle(double r,double l):width(r),heigth(l){}
virtual double area() const{return 0.5*width*heigth;}
protected:
    double width;
    double heigth;
}; 

class Trapezoid:public Shape
{
public:
Trapezoid(double r,double l,double k):top(r),bottom(l),height(k){}
virtual double area() const{return 0.5*(top+bottom)*height;}
protected:
    double top;
    double bottom;
    double height;
}; 

class Square:public Shape
{
public:
Square(double r):side(r){}
virtual double area() const{return side*side;}
protected:
    double side;
}; 

int main()
{
    float r,a,b,w1,w2,w,h;
    cout<<fixed<<setprecision(2);
    cin>>r;
    Circle circle(r);
    cin>>a;
    Square square(a);
    cin>>a>>b;
    Rectangle rectangle(a,b);
    cin>>w1>>w2>>h;
    Trapezoid trapezoid(w1,w1,h);
    cin>>w>>h;
    Triangle triangle(w,h);
    Shape *pt[5]= {&circle,&square,&rectangle,&trapezoid,&triangle};
    double areas=0.0;
    for(int i=0; i<5; i++)
        areas=areas+pt[i]->area();
    cout<<"total of all areas="<<areas<<endl;
    return 0;
} 

虚函数-计算图形面积