[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

12.63.54.5 8.42.0 4.5 3.24.5 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;}