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Lesson 2 Object-oriented programming
Objective Basic concepts behind object-oriented programming.

Object-Oriented Programming in C++

Object-oriented programming (OOP) is a balanced approach to writing software in which data and behavior are packaged together. This encapsulation creates user-defined types, extending and interacting with the native types of the language.

The term OOP refers to a collection of concepts, including the following:
  1. User-defined types can be easily created and used.
  2. Implementation details of user-defined types are hidden.

With OOP, the programming task is frequently more difficult than normal procedural programming, such as in C.
There is at least one extra design step before you get to the coding of algorithms. This extra step involves the design of types that are appropriate for the problem at hand. Frequently, you must solve a problem more generally than is strictly necessary.
The belief is that this will pay dividends in several ways:
  1. The solution will be more self-contained and thus, more robust and easier to maintain and change.
  2. The solution will be more reusable.

Classes and Object-Oriented Programming

You define a new data type by defining a class, but before I get into the language, syntax, and programming techniques of classes, I will explain how your existing knowledge relates to the concept of object-oriented programming. Almost everything you have seen up to now has been procedural programming, which involves programming a solution in terms of fundamental data types. The essence of object-oriented programming (commonly abbreviated to OOP) is that you write programs in terms of objects in the domain of the problem you are trying to solve, so part of the program development process involves designing a set of types to suit the problem context. If you are writing a program to keep track of your bank account, you will probably need to have data types such as Account and Transaction. For a program to analyze baseball scores, you may have types such as Player and Team. The variables of the fundamental types do not allow you to model real-world objects very well. It is not possible to model a baseball player realistically in terms of just an int or double, value or any other fundamental data type. You need several values of a variety of types for any meaningful representation of a baseball player. Classes provide a solution. A class type can be
  1. a composite of variables of other types of fundamental types or
  2. of other class types.
A class can also have functions as an integral part of its definition. You could define a class type called Box that contains variables that store a length, a width, and a height to represent boxes. You could then define variables of type Box, just as you define variables of fundamental types. Each Box object would contain its own length, width and height dimensions and you could create and manipulate as many Box objects as you need in a program.