C++ LANGUAGE BASIC AND DERIVED CLASSES

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C++ LANGUAGE BASIC AND DERIVED CLASSES

Base & Derived Classes 


One of the most important concepts in object-oriented programming 
is that of inheritance. Inheritance allows us to define a class in 
terms of another class, which makes it easier to create and maintain 
an application. This also provides an opportunity to reuse the code 
functionality and fast implementation time. 

When creating a class, instead of writing completely new data 
members and member functions, the programmer can designate that 
the new class should inherit the members of an existing class. 
This existing class is called the base class, and the new class 
is referred to as the derived class. 

The idea of inheritance implements the is a relationship. 
For example, mammal IS-A animal, dog IS-A mammal hence dog 
IS-A animal as well and so on. 


Base & Derived Classes 


A class can be derived from more than one classes, which means 
it can inherit data and functions from multiple base classes. 
To define a derived class, we use a class derivation list to 
specify the base class(es). A class derivation list names one 

or more base classes and has the form: 

class derived-class: access-specifier base-class 

Where access-specifier is one of public, protected, or private, 
and base-class is the name of a previously defined class. 
If the access-specifier is not used, then it is private by default. 

Consider a base class Shape and its derived class Rectangle as follows:
 
#include <iostream> 
  
using namespace std; 
 
// Base class 
class Shape  
{ 
   public: 
      void setWidth(int w) 
      { 
         width = w; 
24. INHERITANCE 
      } 
      void setHeight(int h) 
      { 
         height = h; 
      } 
   protected: 
      int width; 
      int height; 
}; 
 
// Derived class 
class Rectangle: public Shape 
{ 
   public: 
      int getArea() 
      {  
         return (width * height);  
      } 
}; 
 
int main(void) 
{ 
   Rectangle Rect; 
  
   Rect.setWidth(5); 
   Rect.setHeight(7); 
 
   // Print the area of the object. 
   cout << "Total area: " << Rect.getArea() << endl; 
 
   return 0; 
} 
 
When the above code is compiled and executed, it produces the following result: 
Total area: 35