1、實(shí)驗(yàn)三 虛函數(shù)與多態(tài)、純虛函數(shù)  一.實(shí)驗(yàn)?zāi)康?. 在掌握繼承與派生關(guān)系的基礎(chǔ)上，進(jìn)一步理解虛函數(shù)與多態(tài)性的關(guān)系，實(shí)現(xiàn)運(yùn)行時(shí)的多態(tài)。 2. 學(xué)會(huì)定義和使用純虛函數(shù) 二、實(shí)驗(yàn)內(nèi)容1范例：了解"單接口，多方法"的概念?，F(xiàn)有稱(chēng)為figure的基類(lèi)，存放了各二維對(duì)象（三角形、矩形和圓形三個(gè)類(lèi)）的各維數(shù)據(jù)，set_dim()設(shè)置數(shù)據(jù)，是標(biāo)準(zhǔn)成員函數(shù)。show_area()為虛函數(shù)，因?yàn)橛?jì)算各對(duì)象的面積的方法是不同的?！境绦颉?include < iostream > using namespace std;class figureprotected:d

2、ouble x,y;public:void set_dim(double i,double j=0) x=i; y=j; virtual void show_area() cout<<"No area computation defined for this class.n"class triangle:public figurepublic:void show_area() cout<<"Triangle with height "<< x<<" and base "<<

3、y<<" has an area of "<< x*0.5*y<< endl; ;class square:public figurepublic:void show_area() cout<<"Square with dimensions "<< x<<" and "<< y<<" has an area of "<< x*y<< endl; ;class circle:public figur

4、epublic: void show_area() cout<<"Circle with radius "<< x<<" has an area of "<<3.14159*x*x<< endl; ;int main()figure *p; triangle t; square s;circle c;p=&t;p->set_dim(10.0,5.0);p->show_area();p=&s;p->set_dim(10.0,5.0);p->show_area

5、();p=&c; p->set_dim(10.0);p->show_area(); return 0;  【要求】（1） 建立工程，錄入上述程序，調(diào)試運(yùn)行并記錄運(yùn)行結(jié)果。 （2） 修改上述程序，將virtual void show_area()中的virtual去掉，重新調(diào)試運(yùn)行觀察結(jié)果有何變化？為什么？在不使用關(guān)鍵字virtual后，基類(lèi)指針p對(duì)show-area的訪問(wèn)p->show_area()沒(méi)有針對(duì)所指對(duì)象的類(lèi)型調(diào)用不同的函數(shù)，而是直接根據(jù)p的類(lèi)型調(diào)用了基類(lèi)的成員函數(shù)show-area。（3） 修改上述程序入口函數(shù)，使其動(dòng)態(tài)建立三角形、矩形和圓形3個(gè)

6、對(duì)象，通過(guò)基類(lèi)指針訪問(wèn)這3個(gè)對(duì)象，然后釋放這3個(gè)對(duì)象。#include < iostream > using namespace std;class figureprotected:double x,y;public:void set_dim(double i,double j=0) x=i; y=j; virtual void show_area() cout<<"No area computation defined for this class.n"class triangle:public figurepublic:void show_are

7、a() cout<<"Triangle with height "<< x<<" and base "<< y<<" has an area of "<< x*0.5*y<< endl; ;class square:public figurepublic:void show_area() cout<<"Square with dimensions "<< x<<" and "&

8、lt;< y<<" has an area of "<< x*y<< endl; ;class circle:public figurepublic: void show_area() cout<<"Circle with radius "<< x<<" has an area of "<<3.14159*x*x<< endl; ;int main()figure *p;triangle *p1;square *p2;circle *

9、p3;p1=new triangle;p2=new square;p3=new circle;p=p1;p->set_dim(10.0,5.0);p->show_area();p=p2;p->set_dim(10.0,5.0);p->show_area();p=p3;p->set_dim(10.0);p->show_area();delete p1;delete p2;delete p3;（4） 修改類(lèi)定義中的析構(gòu)函數(shù)，使之適應(yīng)用戶動(dòng)態(tài)定義對(duì) 2、使用純虛函數(shù)和抽象類(lèi)對(duì)實(shí)驗(yàn)二中的題1進(jìn)行改進(jìn)。 #include < iostream >using

10、 namespace std;class figureprotected:double x,y;public:void set_dim(double i,double j=0) x=i; y=j; virtual void show_area() cout<<"No area computation defined for this class.n"/在此處將基類(lèi)的析構(gòu)函數(shù)聲明為虛析構(gòu)就OK了virtual figure()/;class triangle:public figurepublic:void show_area() cout<<&quo

11、t;Triangle with height "<< x<<" and base "<< y<<" has an area of "<< x*0.5*y<< endl; ;class square:public figurepublic:void show_area() cout<<"Square with dimensions "<< x<<" and "<< y<<&qu

12、ot; has an area of "<< x*y<< endl; ;class circle:public figurepublic: void show_area() cout<<"Circle with radius "<< x<<" has an area of "<<3.14159*x*x<< endl; ;int main()figure *p; triangle t; square s;circle c;p=&t;p->set_di

13、m(10.0,5.0);p->show_area();p=&s;p->set_dim(10.0,5.0);p->show_area();p=&c; p->set_dim(10.0);p->show_area(); return 0; 2、編程：自定義一個(gè)抽象類(lèi)Element,提供顯示、求面積等公共接口（虛函數(shù)），派生出Point、Line、Circle等圖形元素類(lèi)，并重新定義（override）這些虛函數(shù)，完成各自的任務(wù)。在這里，Element是抽象基類(lèi)，它不能提供具體的顯示操作，應(yīng)將其成員函數(shù)定義為純虛函數(shù)。只有采用指向基類(lèi)的指針或?qū)?lèi)的引用進(jìn)

14、行調(diào)用，實(shí)現(xiàn)的才是動(dòng)態(tài)綁定，完成運(yùn)行時(shí)的多態(tài)性。#include < iostream > using namespace std;const double PI=3.14159;class Elementpublic:virtual const char* Name() const =0;virtual double Area() const =0;class Point:public Elementprotected:double x,y;public:Point(double xv=0,double yv=0):x(xv),y(yv)virtual const char* N

15、ame() constreturn "Point"virtual double Area() constreturn 0;class Line:public Elementprotected:double length;public:Line(double l=0):length(l)virtual const char* Name() constreturn "Line"virtual double Area() constreturn 0;class Circle:public Elementprotected:double radius;public:Circle(double r):radius(r)virtual const char* Name() constreturn "Circle"virtual double Area() constreturn