實驗三虛函數(shù)與多態(tài)純虛函數(shù)

1、-. z實驗三虛函數(shù)與多態(tài)、純虛函數(shù)一.實驗?zāi)康?. 在掌握繼承與派生關(guān)系的根底上，進(jìn)一步理解虛函數(shù)與多態(tài)性的關(guān)系，實現(xiàn)運(yùn)行時的多態(tài)。2. 學(xué)會定義和使用純虛函數(shù)二、實驗容1例：了解單接口，多方法的概念?，F(xiàn)有稱為figure的基類，存放了各二維對象三角形、矩形和圓形三個類的各維數(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)，因為計算各對象的面積的方法是不同的。【程序】#include using namespace std;class figureprotected:double *,y;public:void set_dim(double i,double

2、j=0) *=i; y=j; virtual void show_area() coutNo area putation defined for this class.n;class triangle:public figurepublic:void show_area() coutTriangle with height * and base y has an area of *0.5*y endl; ;class square:public figurepublic:void show_area() coutSquare with dimensions * and y has an are

3、a of *y endl; ;class circle:public figurepublic: void show_area() coutCircle with radius * has an area of 3.14159*set_dim(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; 【要求】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。修改上述程序，將virtual void show_area()中的virtua

4、l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，基類指針p對show-area的p-show_area()沒有針對所指對象的類型調(diào)用不同的函數(shù)，而是直接根據(jù)p的類型調(diào)用了基類的成員函數(shù)show-area。修改上述程序入口函數(shù)，使其動態(tài)建立三角形、矩形和圓形3個對象，通過基類指針這3個對象，然后釋放這3個對象。#include using namespace std;class figureprotected:double *,y;public:void set_dim(double i,double j=0) *=i; y=j; virtual void show

5、_area() coutNo area putation defined for this class.n;class triangle:public figurepublic:void show_area() coutTriangle with height * and base y has an area of *0.5*y endl; ;class square:public figurepublic:void show_area() coutSquare with dimensions * and y has an area of *y endl; ;class circle:publ

6、ic figurepublic: void show_area() coutCircle with radius * has an area of 3.14159*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修改類定義中的析構(gòu)函數(shù)，使之適應(yīng)用戶動態(tài)定義對 2、使用純虛函數(shù)和抽象類對實驗二中的題1進(jìn)展改良。#include using namespace std;cla

7、ss figureprotected:double *,y;public:void set_dim(double i,double j=0) *=i; y=j; virtual void show_area() coutNo area putation defined for this class.n;/在此處將基類的析構(gòu)函數(shù)聲明為虛析構(gòu)就OK了virtual figure()/;class triangle:public figurepublic:void show_area() coutTriangle with height * and base y has an area of *0.

8、5*y endl; ;class square:public figurepublic:void show_area() coutSquare with dimensions * and y has an area of *y endl; ;class circle:public figurepublic: void show_area() coutCircle with radius * has an area of 3.14159*set_dim(10.0,5.0);p-show_area();p=&s;p-set_dim(10.0,5.0);p-show_area();p=&c; p-s

9、et_dim(10.0);p-show_area(); return 0; 2、編程：自定義一個抽象類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，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，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)。只有采用指向基類的指針或?qū)惖囊眠M(jìn)展調(diào)用，實現(xiàn)的才是動態(tài)綁定，完成運(yùn)行時的多態(tài)性。#include using namespace std;const double PI=3.14159;class Elementpublic:virtual c

10、onst char* Name() const =0;virtual double Area() const =0;class Point:public Elementprotected:double *,y;public:Point(double *v=0,double yv=0):*(*v),y(yv)virtual const char* Name() 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 doub