You can declare class members

• Whether they are data items or member functions
  • Either in the public or the private section of a class

 


But because one of the main precepts of OOP is to hide the data

• Data items normally go into the private section

 


The member functions that constitute the class interface

• Go into the public section
  • Otherwise, you can’t call those functions from a program

You can also put member functions

• In the private section
  • You can’t call such functions directly from a program, but the public methods can use them
    • Typically, you use private member functions to handle implementation details that don’t form part of the public interface

You don’t have to use the keyword private in class declarations

• Because that is the default access control for class objects (A-1):
  • However, I will explicitly use the private label in order to emphasize the concept of data hiding

 


Example of (A-1)

class World
{
	float mass; // private by default
	char name[20]; // private by default
public:
	void tellall(void);
	...
};

Classes and Structures

Class descriptions look much like structure declarations

• With the addition of member functions
• And the public and private visibility labels
• In fact, C++ extends to structures the same features classes have

The only difference is that

• The default access type for a structure is public
• Whereas the default type for a class is private

C++ programmers commonly use

• Classes to implement class descriptions while restricting structures to representing pure data objects
• Or, occasionally, classes with no private components