[YTU]_2478( C++习题 虚函数-计算图形面积)

题目描述

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。 

输入

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

输出

所有图形面积之和（结果保留两位小数）

样例输入

12.6
3.5
4.5 8.4
2.0 4.5 3.2
4.5 8.4

样例输出

total of all areas=574.11
#include <iostream>
#include <iomanip>
using namespace std;
class Shape
{
public:
    Shape(){}
    virtual float area()const=0;
};
class Circle:public Shape
{
public:
    Circle(float r):radius(r){}
virtual float area()const {return radius*radius*3.1415926;}
private:
    float radius;
};
class Square:public Shape
{
public:
    Square(float l):liang(l){}
    virtual float area() const{return liang*liang;}
private:
    float liang;
};
class Rectangle:public Shape
{
public:
    Rectangle(float a,float b):chang(a),kuan(b){}
virtual float area()const{return chang*kuan;}
private:
    float chang,kuan;
};
class Trapezoid:public Shape
{
public:
    Trapezoid(float s,float x,float g):shang(s),xia(x),gao(g){}
virtual float area()const{return (shang+xia)*gao*0.5;}
private:
    float shang,xia,gao;
};
class Triangle:public Shape
{
public:
    Triangle(float d,float g):di(d),gao(g){}
virtual float area()const{return di*gao*0.5;}
private:
    float di,gao;
};
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;
}