Engineering Problem Solving With C++ An Object Based Approach

1. Engineering Problem Solving With C++An Object Based Approach Chapter 8 Introduction to Classes

2. Classes • The building blocks of object oriented programming • Include function members and data members • A well designed class is as easy to use as a pre-defined data type

3. Designing a Class • Desired operations • Member functions or methods • constructors • accessor functions • overloaded operators • ... • Required data members

4. Writing a Class Definition • A class definition has two parts • Class declaration • defines name of class, data members, and prototypes for member functions • Class implementation • implements the member functions

5. Class Declaration • Name of the class is specified using the key word class • Body of the class declaration includes • declaration statements for the data members • function prototypes • Keywords public, private and protectedspecify the accessibility of the class members

6. Example - Date Class Declaration #include <iostream> using namespace std; class Date { //class body public: void input(istream&); // I/O methods void print(ostream&) const; void setDate(int mo, int d, int y); int get_day() const; // access methods int get_month() const; int get_year() const; private: int day, month, year; };

7. Date Class • Name of the class is Date • Three private data members • Six public function members • Data members can only be accessed by the member functions

8. Class Implementation • Includes • Function definitions for all function members • Scope Resolution Operator (::) specifies a function as a member of a class

9. Implementation of Date Class #include “Date.h” … void Date::input(istream& in) { in >> month >> day >> year; } void Date::print(ostream& out) const; { out << month <<‘/’ <<day << ‘/’ << year; } void Date::set_date(int m, int d, int y) { month = m; day = d; year = y; }

10. Accessor Functions • Required to access private data members • Complete set should be provided • Our Date class requires 3 accessor functions int get_day() const; int get_month() const; int get_year() const; • const should be placed at the end of any function that is not intended to modify the calling object.

11. Initializing Objects • Constructorfunctions are used to initialize objects at the time they are declared • Called automatically • Same name as the class name • No return value, not even void

12. Constructors for the Date Class • Default Constructor • constructor with no parameters • Prototype: Date(); • Constructor with Parameters • Prototype: Date(int m, int d, int y);

13. Default Constructor • Definition: Date::Date() : month(1), day(1), year(2002) { } • or Date::Date() { month = 1; day = 1; year = 2000; } • First definition is preferred.

14. Constructors With Parameters • Definition Date::Date(int m, int d, int y):month(m), day(d), year(y) { } • or Date::Date(int m, int d, int y) { month = m; day = d; year = y; }

15. Using Programmer Defined Classes • Separate Compilation • Class declaration is saved in a file named classname.h • Class implementation is saved in a file named classname.cpp(or whatever extension your compiler expects) • .h file is included in user program and implementation file • User program is linked to implementation file

16. Using the Date Class #include “Date.h” int main() { Date today(4,6,2002), birthday; //member functions are called using the dot operator birthday.input(cin); today.print(cout); birthday.print(cout); if(today.get_day() == birthday.get_day() && today.get_month() == birthday.get_month() ) cout << “happy birthday!”

17. Practice! Given this definition of a class for a rational number implement the default constructor, parameterized constructor, and the input function. class rational { private: int num, denom; public: rational( ); // initialize to 1/1 rational(int n, int d); void input (istream & istr ) const; void output (ostream & ostr); // write as num/denom bool improper() const; // true if num >= denom };

18. Answer to practice! #include "rational.h" rational::rational( ):num(1),denom(1) { } rational::rational(int n, int d):num(n),denom(d) { } void rational::input (istream & istr ) { istr >> num >> denom; }

19. Operators • Assignment operator is defined for objects of the same type Date d1, d2; d1.input(cin); d2 = d1; • Other operators are not predefined, but can be overloaded in the class definition(see chapter 10) • arithmetic, relational, logical, input and output

20. Helper Functions • Member functions • Called by other member functions • Usually specified as private

21. Example • Design a class to implement a unit vector. A vector object will be represented by an anchor point (the base of the arrow), and an orientation(always between 0 and 360 degrees).  There are 2 manipulations that you can perform on a vector without changing its length. • translate (slide) the vector in the plane, changing its position but not its orientation. • rotate a vector, changing its orientation

22. Translation - change position but not orientation

23. Rotation - change orientation around anchor point

24. Class Declaration class UnitVector { public: UnitVector(); // contstructors UnitVector(double init_x, double init_y, double init_orientation); void rotate(double d_orient);     // rotate the vector void translate(double dx, double dy); // translate the // vector. private: //helper function     void fix_orientation();   // Calculate a legal orientation      double x, y;                   // The anchor point of the object.      int orientation; //orientation };

25. Class Implementation //Constructor functions UnitVector::UnitVector(double initial_x, double initial_y, double initial_orientation) : x(initial_x), y(initial_y), orientation(initial_orientation) { fix_orientation(); } UnitVector::UnitVector( ): x(0), y(0), orientation = 0; { }

26. Member Function Definitions // rotate the calling vector void UnitVector::rotate(double d_orient)       { orientation += d_orient; fix_orientation(); } // translate the calling vector void UnitVector::translate(double dx, double dy) { x += dx; y += dy; }

27. Helper Function Definition //This function adjusts the orientation value //Original orientation may be < 0 or >= 360) //Adjusted orientation is 0<=orientation < 360. void UnitVector::fix_orientation()   { if(orientation < 0) orientation = 360 + orientation%360; else orientation = orientation%360; }

28. Passing Objects To Functions • Objects may be passed either "by value" or "by reference" • Example: bool UnitVector::ShareBasePoint(UnitVector v)const ( if (x == v.x && y == v.y) return true; else return false; }

29. Practice! Which of the statements on the right is valid within a main program which contains an include for this header file. class rational { private: int num, denom; int LCD( ); public: rational( ); rational(int n, int d); void input (istream & istr ); void output (ostream & ostr) const; void reduce ( ); }; • rational A; • rational B(5, 9); • input(A); • B.output(cout); • int div=B.LCD(); • A.denom = 3; • B.reduce;    