Computer Programming II Lecture 5

Introduction to Object Oriented Programming (OOP) - There are two common programming methods : procedural programming and object-oriented programming (OOP). - Procedural programming : In a procedural program data is typically stored in a collection of variables and there is a set of functions that perform operations on the data. The data and the functions are separate entities. - Object-oriented programming : is centered around objects that encapsulate both data and the functions that operate on them.

Object Oriented Programming (OOP) There are a few principle concepts that form the foundation of object-oriented programming : 1- Abstraction : - An abstraction is a general model of something. It is a definition that includes only the general characteristics of an object without the details that characterize specific instances of the object. - An abstract data type (ADT) is a data type that specifies the values the data type can hold and the operations that can be done on them without the details of how the data type is implemented.

Object Oriented Programming (OOP) 2- Class: A class is a programmer-defined data type that describes what an object of the class will look like when it is created. It consists of a set of variables and a set of functions. 3- Objects: Objects are instances of a class. They are created with a definition statement after the class has been declared. 4- Encapsulation : Encapsulation is placing the data and the functions that work on that data in the same place.

Object Oriented Programming (OOP) 5- Inheritance: - Inheritance allows to create classes which retain characteristics of the base class. - Inheritance involves a base class and a derived class. The base class is the general class and the derived class is the specialized class. The derived class is based on, or derived from, the base class. 6- Polymorphism: In programming languages, polymorphism means that some code or operations or objects behave differently in different contexts.

Classes and objects : - In C++, the class is the construct primarily used to create objects. - A class is a programmer-defined data type that describes what an object of the class will look like when it is created. It consists of a set of variables and a set of functions.

Classes and objects : Declaration: Classes are generally declared using the keyword class, with the following format: class class_name { access_specifier_1: member1; access_specifier_2: member2;... } object_names;

Classes and objects : - Where class_name is a valid identifier for the class, object_names is an optional list of names for objects of this class. The body of the declaration can contain members, that can be either data or function declarations, and optionally access specifiers. - An access specifier is one of the following three keywords: private, public or protected.

Classes and objects : - These specifiers modify the access rights that the members following them acquire: private members of a class are accessible only from within other members of the same class or from their friends. protected members are accessible from members of their same class and from their friends, but also from members of their derived classes. Finally, public members are accessible from anywhere where the object is visible.

Classes and objects : Example: class Crectangle { private: int x, y; public: void set_values (int a, int b); int area ( ); } rect;

Classes and objects : Accessing an Object’s Members: - Public members of a class object are accessed with the dot operator (.). - After the previous declarations of CRectangle and rect, we can refer within the body of the program to any of the public members of the object rect as if they were normal functions or normal variables, just by putting the object's name followed by a dot (.) operator and then the name of the member. For example : rect.set_values (3,4); myarea = rect.area();

This program is used to calculate the area of rectangle.

Classes and objects : Types of Member Functions: - Accessor, get, getter function: uses but does not modify a member variable. - A function that uses the value of a class variable but does not change it, is known as an accessor. - Mutator, set, setter function: modifies a member variable. - A function that stores a value in a member variable or changes its value, is known as a mutator.

Classes and objects : Defining Member Functions: - Member functions are part of a class declaration. Class member functions can be defined either inside or outside the class declaration. - When a class function is defined within the class declaration, it is called an inline function. Inline functions provide a convenient way to contain function information within a class declaration, but they can only be used when a function body is very short, usually a single line.

Classes and objects : - When a function body is longer, a prototype for the function should appear in the class declaration, instead of the function definition itself. The function definition is then placed outside the class declaration. - In the function definition, precede function name with class name and scope resolution operator ( :: ) - The ( : : ) symbol is called the scope resolution operator. It is needed to indicate that these are class member functions and to tell the compiler which class they belong to.

Classes and objects :

Write a C++ program to create a class called rectangle which used to calculate the area of rectangle. Note : Length and width are inserted by user. Area = Length * width.