C++

1. C++ Lecture 4 Tuesday, 15 July 2003

2. Struct & Classes • Structure in C++ • Classes and data abstraction • Class scope • Constructors and destructors • Examples

3. OOP Key Concepts • OOP encapsulates data (attributes) and function (behavior) into packages called classes. • Class is like a blueprint of house. One can build many houses (of the same type) with one blueprint. • Out of a class, programmer can create object.

4. Structure Definition struct Time { int hour; int minute; int second; };

5. Declaration Time timeObject, // a variable timeArray[10], // array *timePtr, // pointer to... &timeRef = timeObject; // ref

6. Accessing Members of Structure cout << timeObject.hour; cout << timeRef.hour; timePtr = &timeObject; cout << timePtr -> hour; cout << (*timePtr).hour; // the same

7. Example Fig.6.1 • Structure - declaration and use. • Conditional expression expr ? A : B • the value is A if expr is true and B if expr is false. C.f. Fig.6.1.

8. Abstract Data Type with a Class class Time { public: Time(); // constructor void setTime(int, int, int); void printMilitary(); void printStandard(); private: int hour; int minute; int second; };

9. Declaration of Objects of Type "Time" Time sunset, // object of type Time arrayOfTimes[5], // array of Time obj *ptrToTime, // pointer to Time obj &dinnerTime = sunset; // reference

10. What is an Object? • Object is a variable, • Object is a function? • Object is data and functions • Object is an abstraction of something that has attributes (property) and operations (function calls).

11. Member Functions • Member functions of Time are defined outside the class with :: binary scope resolution operator. • E.g., void Time::setTime(int h, int m, int s) { hour = ( h>= 0 && h < 24) ? H : 0; ... }

12. Class Example Fig.6.3 • Class definition • Member function definition • Main program C.f. Fig. 6.3.

13. Class Scope • Class data members and member functions belong to that class's scope. • Within a class's scope, class members are references by name. • Outside a class's scope, class members are referenced through one of the handles on an object.

14. The Handles • Use dot (.) notation for object and references. • Use arrow (->) for pointer to the object • E.g., c.x , cpt -> x C.f. Fig. 6.4

15. Separating interface from implementations • Header files contains class declarations only • Class function definition in source file • Driver program in another file

16. Public and Private Data or Function • Public data or functions are accessible from outside • Private data or functions are not directly accessible by the user outside the class scope • Public functions are used as an interface to access or modify private data

17. Initializing Class Objects with Constructors • A constructor is a class member function with the same name as the class. • The constructor is called whenever an object of that class is created. • The constructor does not return a value (not even void).

18. Destructors • The name of the destructor for a class is the tilde (~) character followed by the class name. • Destructor is called when an object is going to disappear (out of scope).

19. When Constructors and Destructors are Called • Example of Fig. 6.15-17, constructor and destructor of a class. C.f. Fig. 6.15-17.

20. Default Constructor class Time { public: Time(); // default constructor Time(int, int, int); …. } Used as Time t, t(12, 06, 0); C.f. Fig.18-20

21. Assignment by Default Memberwise Copy • If date1 and date2 are objects of the same type, we can say date2 = date1; • The date members values are copied memberwise. C.f. Fig.6.24

22. Questions • In the class assignment example, if the member data are arrays, are the values of the array elements copied? • If it is a pointer, is the pointer value (address) copied? • If a pointer pointing to an array, are the values of array elements copied?

23. Copy Constructor • You can override what the class assignment a=b means by write a so-called copy constructor • We declare and implement a function, e.g., for the class Date Date(Date &d) C.f. an example in Fig.8.4-8.6

24. Problems • Find error(s) in each of the following and explain how to correct it. • Assuming the following prototype is declared in class Time. • void ~Time(int);

25. Problems • Find error(s) - The following is a partial definition of class Time: class Time { public: // function prototypes private: int hour = 0; int minute = 0; int second = 0; };

26. Problems • Find error(s) – Assuming the following prototype is declared in class Employee: int Employee(const char *, const char *)