Introduction to Object-Oriented Programming

Programming:

Evolution of languages:

• Machine languages -- this is what is necessary for the computer, but hard for people to read
• Assembly languages -- these are symbolic translations of machine code, easier for people to read
• High-level procedural languages (like Pascal, Fortran, C)
• Object Oriented languages  (C++, Java, Smalltalk)

Computers need machine code instructions, but programmers would like to read and write programs on a higher level.  High-level languages like C and Pascal are also known as procedural languages.  They allow the writing of procedures and functions for code modularity, often dividing the work into separate actions.  High level languages are much more readable for programmers.  Since the computer still needs machine code instructions, high-level languages are usually run through a compiler, which translates high-level code into the machine's own instructions.

Object-oriented languages, like C++ and Java, take this a step further and encapsulate their data and procedures together in units called objects, which contain more than just functions (actions, often representable by verbs).  These languages make items modular as well (objects, or things representable by nouns).  Object-oriented languages are also high-level languages, more readable for people, and needing translation for the machine (by a compiler or interpreter).

C is a high-level procedural programming language.
C++ is an object-oriented programming language based on C.
 

Classes and Objects:

• Object -- an encapsulation of data and functions that act upon that data. The three aspects of an object:
  • Name -- the variable name we give it
  • Attributes (member data) -- the data that describes the what the object is
  • Behavior (member functions) -- behavior aspects of the object (functions that describe what the object does)
• Class -- a blueprint for objects. A class is a user-defined type that describes what a certain type of object will look like. A class description consists of a declaration and a definition (usually split into separate files).
• An object is a single instance of a class.
  You can create many objects from the same class type, in much the same way that you can create many houses from the same blueprint.

What's so special about objects?

• Name -- the variable name we give it
• Attributes -- data stored inside the struct

So, what's the difference?

• In C, data and functions are separate
• In C++, you can build obects that encasulate data and functions together

C++ libraries can contain useful classes of objects that store data in useful and reusable ways.  Classes become building blocks for use in other programs.