Introduction and Basics in

1. Introduction and Basics in Object Oriented programming

2. Object Oriented Paradigm • Centers on the idea of all programs can be made up of separate entities (Objects) team up to exact units (Classes) .. WHY!!!! • Student (class): Sara, Amal, Nora, and Nada (objects) • Course (class): CS140, CS141, and CS 202 (objects) • Way of refereeing to the related collection of data within a unit (class) by a single variable name (object) • Sara (object): name (data 1), ID (data 2) and GPA (data 3) • Which is the unit here?

3. Class • A user-defined data type that combine data and operations in a single unit • Encapsulation • Considered as an object factory which can be generate a number of similar objects • Share the same meaning, attributes (state) and operations (behavior) • Syntax: ClassclassNameIdentifier { //member functions //data members };

4. Class Members • Can be data or functions • Each class member has a visibility • Indicated by access specifiers • Private: members of a class not accessible outside that class • Perform data hiding • By default, all members in a class are private • Public: members of a class accessible outside that class

5. Class Members - Data • Known as attributes; declared like any other variables but can’t be initialized in the definition • Can be built-in data types or user-defined data types • Hold information for each object • Each object has its own copy of data members • Exist throughout the life of the object • Have the same name in all object but might have different values • Example: Class Student { // ---here member functions--- private: string name; int ID; double GPA; };

6. Class Members - Functions • Known as methods; any function belong to class definition • Must be declared inside a class definition but can be defined outside that class definition • Outside class: by tide function name with class name via scope resolution operator (::) • Syntax: //Outside class returnType className::funName(parameters list) {body} • Follow the same regulations of functions in structured programming .. List them!!!

7. Class Members - Functions • Types • Access functions: mutators, accessors and predicate functions • Mutators and accessors allow to interact with private data members either inside or out side class scope • Mutators may perform validation .. WHY here!!! • Utility functions • Local variable • Declared in a member function definition's body • Used only inside a member function • Its value lost when a member function terminates • When have the same name of data members • Precede data members with scope resolution operator (::)

8. Class Members - Functions (Cont.) • Example: Class Student { public: //Accessors string getName(); int getID(); double getGPA(); //Mutators void setName(string name); void setID(int m=0); void setGPA(double g); //predicate bool isRegistered(); //Utility bool validateName(string n); private: string name; int ID; double GPA; };

9. Class Members - Functions (Cont.) • Example: //File scope string Student::getName() { return name; } int Student::getID() { return ID; } double Student::getGPA() { return GPA; } void Student::setName(string name) { if(validateName(name)) ::name=name; else ::name= “”; } void Student::setID(double m=0) { ID=m; } void Student::setGPA(double g ) { GPA=g; } bool Student::isRegistered() { if( ID != 0 ) return true; elsereturn false; } bool Student::validateName(string n); { if( n.length() > 15 ) return false; elsereturn true; }

10. Object • An object is a unique instance of a class Student Class Sara Amal name sara name amal ID ID 43011 43012 4.8 3.12 GPA GPA

11. Object (Cont.) • Can’t use any class members until create an object of that class • To access an object’s public members by using • Dot operator (.) • Used with an object’s name or with a reference to an object • Example: //main function Student Sara; Sara.setID();

12. Constructor • Special member function used to initialize an object’s data once created • It has: • The same name of a class • No return type; not even void • Can be overloaded • Syntax: public:className( parameter list) {constructor body}

13. Default Constructor • Has no parameters • Two ways to provide a default constructor • By programmer; defines a default constructor explicitly • By compiler; generate a default constructor implicitly, if no constructors are provided for a class • Only initialize string data members to null string • Example: public: Student(){name=“N/A”; ID=0; GPA=0.0;}

14. Parameterized Constructor • Allow to create a new object of a class while concurrently passing arguments to that object • Must supply the arguments to the constructor if no default arguments are provided • Example: public: Student(string n, int m, double g=0.0) {name=n; ID=m; GPA=g;}

15. Do Use each access specifier only once in class definition Perform least privilege .. !!! Don’t Define a function inside another function Define a function parameter again as a local variable Initialize a data member of a class explicitly Do .. Don’t - Common errors

16. Exercise -1 Write a class called Pen, which has two attributes: inkLevel, and color. A new pen always comes with inkLevel of 10, while the color is different from one pen to another. In addition to the constructor, a pen has a method called write which reduces the level of the ink the pen by 1, then returns the current inkLevel. A refill method sets the inkLevel to 10. Finally, a display method prints on the screen the details of the pen (its color and inkLevel).

17. Exercise -2 Write a WebPage class which includes: • The following integer data members: • Number of hits on the page • Number of messages posted on the page • Number of downloads from the page • The following member functions • Default constructor initializes all data members to zero • Parameterized constructor initializes all data members to received values • An increment function for each data members to increase them by 1 • Activity() function that return total activity of webpage: hits + messages + downloads • Write a main function that declare and initialize imamUnivPage object. • Write the statements that increase number of hits by 2, messages by 3, and downloads by 1. • Display the number of hits, messages, and downloads for the page as well as the total activity.