Solved

c++ polymorphism function

Posted on 2006-11-30
3
198 Views
Last Modified: 2010-04-01
Hello, I found the following code from one of the experts here, but I don't understand a lot of it.  Could someone please help me understand what the program is doing?  I understand the basics, but need help with understanding these lines.  I am not sure what teh ~ means.  Please help me understand.  

class Shape
{
public:
     Shape() {};
     virtual ~Shape() {};
     virtual void DrawShape() = 0;
};

class Circle : public Shape
{
public:
     Circle() {};
     virtual ~Circle() {};
     virtual void DrawShape() { cout << "This is a circle" << endl; }
};




-----------------------------------------------
Here's the code someone wrote:
-----------------------------------------------
#include <iostream>

using namespace std;

class Shape
{
public:
     Shape() {};
     virtual ~Shape() {};
     virtual void DrawShape() = 0;
};

class Circle : public Shape
{
public:
     Circle() {};
     virtual ~Circle() {};
     virtual void DrawShape() { cout << "This is a circle" << endl; }
};

class Triangle : public Shape
{
public:
     Triangle() {};
     virtual ~Triangle() {};
     virtual void DrawShape() { cout << "This is a triangle" << endl; }
};

class Rectangle : public Shape
{
public:
     Rectangle() {};
     virtual ~Rectangle() {};
     virtual void DrawShape() { cout << "This is a rectangle" << endl; }
};

int main()
{
     Shape* pShape = 0;
     int ask = 0;
     cout <<"=============================================="<<endl;
     cout << "Do you want to display (type 1,2,or 3):" <<endl;
     cout << "1. Circle"                                             <<endl;
     cout << "2. Triangle"                                   <<endl;
     cout << "3. Rectangle"                                             <<endl;
     cout <<"----------------------------------------------"<<endl;
     cin >> ask;
       cin.get();
     
     switch (ask)
     {    
     case 1:
          pShape = new Circle;
          break;
              cin.get();
     case 2:
          pShape = new Triangle;
          break;
              cin.get();
     case 3:
          pShape = new Rectangle;
          break;
              cin.get();
     default:
          cout << "Invalid choice.  Good-bye!" << endl;
              cin.get();
          return -1;
             
     }
     pShape->DrawShape();
     delete pShape;
       cin.get();

     return 0;
}
0
Comment
Question by:meaar
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
3 Comments
 
LVL 45

Accepted Solution

by:
sunnycoder earned 500 total points
ID: 18051859
Hi meaar,

~<functionName>
Where functionName is same as class name signifies destructor ...

Class Shape has 3 members ... a constructor which is empty and does nothing ...
A virtual destructor .... why we need a virtual destructor
http://blogs.msdn.com/oldnewthing/archive/2004/05/07/127826.aspx
http://www.codersource.net/cpp_virtual_destructors.html

And third member is a pure virtual function DrawShape() .. Note the =0. Pure virtual function is one whose implementation is mandatory for every class that derives from Shape class ...

Class Circle derives from Shape ... again an empty constructor and a virtual destructor ...
Since it derives from Shape, it provides an implementation for DrawShape - the pure virtual function in parent class ..

Now if you have
Shape * ptr;
Circle obj1;

ptr = &obj1;
ptr->DrawShape(); //this call will print "this is a circle"

Cheers!
sunnycoder
0
 

Author Comment

by:meaar
ID: 18051874
sunnycoder, your answer was nice you had to send it twice. :)
0
 
LVL 45

Expert Comment

by:sunnycoder
ID: 18051974
:) ...

It reported failure on first attempt which as I discovered later was successful.

Deleted the duplicate post.

sunnycoder
Page Editor
0

Featured Post

Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Written by John Humphreys C++ Threading and the POSIX Library This article will cover the basic information that you need to know in order to make use of the POSIX threading library available for C and C++ on UNIX and most Linux systems.   [s…
This article will show you some of the more useful Standard Template Library (STL) algorithms through the use of working examples.  You will learn about how these algorithms fit into the STL architecture, how they work with STL containers, and why t…
The viewer will learn how to use the return statement in functions in C++. The video will also teach the user how to pass data to a function and have the function return data back for further processing.
The viewer will be introduced to the technique of using vectors in C++. The video will cover how to define a vector, store values in the vector and retrieve data from the values stored in the vector.

696 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question