C,C++,C#

What is the difference between class and structure?

Structure: Initially (in C) a structure was used to bundle different type of data types together to perform a particular functionality. But C++ extended the structure to contain functions also. The major difference is that all declarations inside a structure are by default public.
Class: Class is a successor of Structure. By default all the members inside the class are private.


What is RTTI?

Runtime type identification (RTTI) lets you find the dynamic type of an object when you have only a pointer or a reference to the base type. RTTI is the official way in standard C++ to discover the type of an object and to convert the type of a pointer or reference (that is, dynamic typing). The need came from practical experience with C++. RTTI replaces many homegrown versions with a solid, consistent approach.


What is encapsulation?

Packaging an object’s variables within its methods is called encapsulation.


Explain term POLIMORPHISM and give an example using eg. SHAPE object: If I have a base class SHAPE, how would I define DRAW methods for two objects CIRCLE and SQUARE

Answer1

POLYMORPHISM : A phenomenon which enables an object to react differently to the same function call.
in C++ it is attained by using a keyword virtual

Example

public class SHAPE
{
public virtual void SHAPE::DRAW()=0;
}
Note here the function DRAW() is pure virtual which means the sub classes must implement the DRAW() method and SHAPE cannot be instatiated

public class CIRCLE::public SHAPE
{
public void CIRCLE::DRAW()
{
// TODO drawing circle
}
}
public class SQUARE::public SHAPE
{
public void SQUARE::DRAW()
{
// TODO drawing square
}
}
now from the user class the calls would be like
globally
SHAPE *newShape;

When user action is to draw
public void MENU::OnClickDrawCircle(){
newShape = new CIRCLE();
}

public void MENU::OnClickDrawCircle(){
newShape = new SQUARE();
}

the when user actually draws
public void CANVAS::OnMouseOperations(){
newShape->DRAW();
}

Answer2

class SHAPE{
public virtual Draw() = 0; //abstract class with a pure virtual method
};

class CIRCLE{
public int r;
public virtual Draw() { this->drawCircle(0,0,r); }
};

class SQURE
public int a;
public virtual Draw() { this->drawRectangular(0,0,a,a); }
};

Each object is driven down from SHAPE implementing Draw() function in its own way.