CMSC 202 Computer Science II for Majors

CMSC 202UMBC Topics Objects and Classes Project 2 description

CMSC 202UMBC Objects What are objects ?  Real-world objects E.g. Car, Fruit A real-world object is an entity in the world  An object is an entity in an OO system  OO programming approach Programming problem is in terms of objects and communication between them

CMSC 202UMBC Class A Class is a user-defined data type whose instances are objects Objects are variables of type class Thus, class is an abstraction of objects of similar type E.g. automobile is a class whose objects could be Bob’s car, Mary’s car etc.

CMSC 202UMBC Class … cont One important feature of class is Data hiding or Encapsulation A class wraps data and functions into a single unit Thus data is typically not accessible to outside world Member functions provide an interface between object’s data and program

CMSC 202UMBC Class … cont Object User of objects Member Functions Member Variables ( Data ) An Interface

CMSC 202UMBC Class … cont Syntax class class-name { access-specifier : data and functions access-specifier : data and functions access-specifier : data and functions … } ;

CMSC 202UMBC Class … cont Access – specifier  private : Private to class  public : Accessible to other parts of program  protected : Needed in inheritance (later) By default, all members are private

CMSC 202UMBC Class … cont E.g. of a class named Date class Date { public : // public member functions Date (int month=1, int day=1, int year=2003); void Print ( void ) const; private : // private data members int m_month; int m_day; int m_year; };

CMSC 202UMBC Class … cont Defining constructor & member functions Date :: Date (int month, int day, int year) { m_month = month; m_day = day; m_year = year; } void Date :: Print ( void ) const { cout << month << “-” << day << “-” << year; }

CMSC 202UMBC Class … cont In C++, you can add new features to existing structure of object / class Suppose we need to add a member function called NextDay  NextDay increments day by 1  Where do we make changes in the class ?

CMSC 202UMBC Class … cont class Date { public : // public member functions Date (int month=1, int day=1, int year=2003); void Print ( void ) const; void NextDay( void ); private : // private data members int m_month; int m_day; int m_year; };

CMSC 202UMBC Class … cont Defining NextDay member function void Date :: NextDay ( void ) {..// logic to increment date..// Also need to consider incrementing to next // month and next year }

CMSC 202UMBC Class … cont Declaring an object as data member of another class  A class is a data-type, a class can use an object as a data member  This is known as aggregation or composition  Consider adding a Time object in our Date class  Exercise 6.10 on page 466

CMSC 202UMBC Class … cont class Time { public : // Constructor and all member function will come // here // Function to increment time by one second void Increment ( void ); private : int m_hour; int m_minute; int m_second; };

CMSC 202UMBC Class … cont class Date { public : // Constructor and all member function will come // here // Add member function Tick which calls Increment void Tick ( void ); private : Time currentTime; // Declare Time object in Date // other data members };

CMSC 202UMBC Class … cont How is the Tick() member function defined ? void Date :: Tick ( void ) {..// logic to increment date // This is how we make use of Increment function of Time class currentTime.Increment(); } But you still cannot access private members of Time class from Date class - Encapsulation

CMSC 202UMBC Class … cont m_month m_day m_year m_hour m_minute m_second Date Object Time Object User Member Functions Member Func

CMSC 202UMBC Project 2 Objective  To implement and use objects  To understand aggregation  To practice formatted output, makefiles Given a quadrilateral, it can be a  Parallelogram  Rectangle  Square  Trapezoid  Irregular

CMSC 202UMBC Project 2 … cont Classes  A Point class Encapsulates x and y co-ordinates of a point  A Quadrilateral class Encapsulates a quadrilateral Uses Point class for each of its four corners The corners are referred as ‘UpperRight’, ‘UpperLeft’, ‘LowerLeft’ and ‘LowerRight’

CMSC 202UMBC Project 2 … cont What you need to do ?  Accept x and y co-ordinates of four corners  Classify the quadrilateral as one of the five types  Compute and display its area and perimeter Assume  Co-ordinate values are integers  Base is parallel to x axis  Area of irregular quadrilateral is

CMSC 202UMBC Project 2 … cont Sample run (taken from Project 2 description) linux3[3]% Proj2 This is my optional greeting Please enter x- and y-coordinates of the UpperLeft corner: 6 4 Please enter x- and y-coordinates of the LowerLeft corner: 9 1 Please enter x- and y-coordinates of the LowerRight corner: 16 1 Please enter x- and y-coordinates of the UpperRight corner: 13 4 The Quadrilateral's Corners Upper Left: ( 6, 4) Upper Right: (13, 4) Lower Left: ( 9, 1) Lower Right: (16, 1) This Quadrilateral is a Parallelogram Area: Perimeter: linux3[4]%