C++ model - OO, OB

1. The procedural model as programmed in C, and, of course, supported within C++. An example of this is string manipulation using character arrays and the family of str* functions defined in the Standard C library:

   char boy[] = "Danny"; 
   char *p_son; 
   
   ... 
   
   p_son = new char[ strlen( boy ) + 1 ]; 
   strcpy( p_son, boy ); 
   
   ... 
   
   if ( !strcmp( p_son, boy )) 
      take_to_disneyland( boy ); 

2. The abstract data type (ADT) model in which users of the abstraction are provided with a set of operations (the public interface), while the implementation remains hidden. An example of this is a String class:

   String girl = "Anna"; 
   String daughter; 
   
   ... 
   
   // String::operator=(); 
   daughter = girl; 
   
   ... 
   
   // String::operator==(); 
   if ( girl == daughter ) 
      take_to_disneyland( girl ); 

3. The object-oriented (OO) model in which a collection of related types are encapsulated through an abstract base class providing a common interface. An example of this is a Library_materials class from which actual subtypes such as Book, Video, Compact_Disc, Puppet, and Laptop are derived:

   void 
   check_in( Library_materials *pmat ) 
   { 
      if ( pmat->late() ) 
           pmat->fine(); 
      pmat->check_in(); 
      if ( Lender *plend = pmat->reserved() ) 
           pmat->notify( plend ); 
   } 

C++ supports polymorphism through class pointers and references. This style of programming is called object-oriented.
C++ also supports a concrete ADT style of programming now called object-based (OB)—nonpolymorphic data types, such as a String class.