实验6多态性与虚函数

[实验目的]1、了解多态性的概念；2、了解虚函数的用途及使用方法；3、了解纯虚函数和抽象类的概念和用法。

[实验要求]给出以下各实验内容的源程序代码，并把编译、运行过程中出现的问题以及解决方法填入实验报告中，按时上交。

[实验学时]2学时。

[实验内容]1、写一个程序，定义抽象基类Shape，由它派生出3个派生类：Circle(圆形)、Square(正方形)、Rectangle(矩形)。

利用指针、虚函数printArea()分别输出以上三者的面积，3个图形的数据在定义对象时给定。

[源程序]#include<iostream>using namespace std;class Shape{public:virtual float area()const=0;virtual void display()const=0;};class Circle:public Shape{public:Circle(double a):r(a){}virtual float area()const{return 3.14*r*r;}virtual void display()const{cout<<"圆面积"<<area()<<endl;}private:double r;};class Rectangle:public Shape{public:Rectangle(double a,double b):l(a),w(b){}virtual float area()const{return l*w;}virtual void display()const{cout<<"矩形面积"<<area()<<endl;}private:double l;double w;};class Square:public Shape{public:Square(double a):a1(a){}virtual float area()const{return a1*a1;}virtual void display()const{cout<<"正方形面积"<<area()<<endl;}private:double a1;};int main(){Circle c1(5);Rectangle r1(5,8);Square s1(2.5);Shape *p[3]={&c1,&r1,&s1};int i;double m=0.0;for (i=0;i<3;i++){p[i]->display();m=m+p[i]->area();}cout<<"总面积:"<<m<<endl;}2、定义Point(点)类，由Point类派生出Circle(圆)类，再由Circle类派生出Cylinder(圆柱体)类。

将类的定义部分分别作为3个头文件(.h文件)，对它们的成员函数的声明部分分别作为3个源文件(.cpp文件)，在主函数(.cpp 文件)中用#include命令把它们包含进来，形成一个完整的程序，并上机运行。

[源程序]//Point.hclass Point{public:Point(float a=0,float b=0);void display();protected:float x,y;};//Point.cpp#include<iostream.h>#include"Point.h"Point::Point(float a,float b){x=a;y=b;}void Point::display(){cout<<"Point:"<<endl<<"x="<<x<<endl<<"y="<<y<<endl;}//Circle.hclass Circle:public Point{public:Circle(float x=0,float y=0,float r=0);void display();protected:float radius;};//Circle.cpp#include<iostream.h>#include"Point.h"#include"Circle.h"Circle::Circle(float a,float b,float r):Point(a,b),radius(r){}void Circle::display(){cout<<"Circle:"<<endl;cout<<"x="<<x<<endl;cout<<"y="<<y<<endl;cout<<"radius="<<radius<<endl;cout<<"area="<<radius*radius*3.14<<endl;cout<<endl;}//Cylinder.hclass Cylinder:public Circle{public:Cylinder (float x=0,float y=0,float r=0,float h=0);void display();protected:float height;};//Cylinder.cpp#include<iostream.h>#include"Point.h"#include"Circle.h"#include"Cylinder.h"Cylinder::Cylinder(float a,float b,float r,float h):Circle(a,b,r),height(h){} void Cylinder::display(){cout<<"Cylinder:"<<endl;cout<<"x="<<x<<endl;cout<<"y="<<y<<endl;cout<<"radius="<<radius<<endl;cout<<"height="<<height<<endl;cout<<"area="<<2*radius*radius*3.14+2*3.14*radius*height<<endl;cout<<"volume="<<radius*radius*3.14*height<<endl;cout<<endl;}//Main.cpp#include <iostream.h>#include"Point.h"#include"Circle.h"#include"Cylinder.h"int main(){Point p(2.0,4.0);p.display();Circle c(4.0,5.0,6.0);c.display();Cylinder cy(7.0,8.0,10.0,11.0);cy.display();return 0;}3、要求正方体、球、圆柱的表面积，可以抽象出一个公共的基类Container 为抽象类，在其中定义一个公共的数据成员radius(此数据可以作为正方形的边长、球的半径、圆柱体底面圆半径)，以及求表面积的纯虚函数area()。

由此抽象类派生出要描述的三个类，利用基类指针和虚函数，分别计算三种图形的表面积。

[源程序]#include <math.h>#include <iostream.h>#define PI 3.14class Cshape{double radius,height;double area,vol;int name;public:Cshape(double r,double h){radius = r;height = h;name = 3;}Cshape(double r){radius = r;name = 1;}void DisAttr(){if(name == 1)cout<<"球体信息"<<endl;if(name ==2)cout<<"正方形信息"<<endl;cout<<"表面积是："<<area<<endl;}void DisAttr(int flag){cout<<"圆柱信息"<<endl;cout<<"表面积是："<<area<<endl;}void Sarea(){area = 4*PI*pow(radius,2);}void Sarea(int cube){area = 6*pow(radius,2);}void Sarea(double cube){name = 3;area = 2*PI*pow(radius,2)+2*PI*radius*height; }};int main(){Cshape yuanqiu(3); yuanqiu.Sarea(); yuanqiu.DisAttr(); Cshape zhengfangxing(3); zhengfangxing.Sarea(1); zhengfangxing.DisAttr(); Cshape yuanzhu(3,4); yuanzhu.Sarea(12.3); yuanzhu.DisAttr(1); return 0;}。