1. Constructors Member Functions Inheritance
Classes - Part II
Constructors
Member Functions
Inheritance

2. Classes
Structured Programming 256
Chapter 9

3. Class Implementation
A constructor is a special member function provided to allow initialization of variables.

4. Constructors
constructor initializes private data when a class object is created
Example TimeType(int, int, int);
Student(double, char, char, char, char);

5. Default Constructors
default constructor parameterless constructor, it initializes the variables to some default value, such as zero
Example TimeType();
Student();

6. Default Constructor Function
same
Syntax
Classname::Classname( ) {
function body } *

7. Constructor Functions
do NOT have a return type (not even void)
must have the same name as the class itself
invoked when you declare an instance of a class with a list of initial values
there should be a default constructor
* * * *

8. Default Constructor Function
Example 1
TimeType::TimeType( ) {
hrs = 0;
mins = 0;
secs = 0; }
Example 2
Student::Student( ) {
GPA = 0;
num_of_grades = 130; }
* *

9. Default Constructor Function
Example 3
Circle::Circle( radius) {
radius_of circle = radius;
x_center = 5;
y_center = -3; }
Example 4
Student::Student( ) { }
* *

10. Destructors ~Classname( )
A default do-nothing destructor is provided by the compiler.
Only one destructor per function class
No arguments - no return values

11. Some Terminology OOP C++ object class object or class instance
instance variable private data member
method public member function
message passing function call (to a public member function)

12. Review - In Specification File
default constructor Classname(); Track();
constructor Classname(type para, type para , ...); Track(int disc, double hurdles);
member function type Function(type para , type para , ...); void Event(double hurdles);
h file
* * *

13. Review - In Implementation File
constructor Classname::Classname(type para, type para , ...) Track::Track(int disc, double hurdles)
member function type Function(type para , type para , ...) void Event(double hurdles)
default constructor Classname::Classname() { } Track::Track() { }
all have a body
* *

14. Review - In Client File
default constructor If NOT passed parameters - gets called when declaring an object of type Class.
constructor If passed parameters - gets called when declaring an object of type Class.
member function object.Function(para , para , ...); b_jenner.Event(double hurdles);
* * *

15. Inheritance creating new classes out of existing ones
reuse code without need for retesting and validation
speeds up programming process
simple vs. multiple

16. Inheritance - simple Circle base class: derived class: Sphere Cylinder*

17. Inheritance - multiple
base
classes:
derived
class:
Car
Truck
Minivan *

18. Constructor Function Call
Syntax Classname object(arguments);
or Classname object = Classname(arguments);
* *

19. Constructor Function Call
Example Circle big_circ(0, ); Circle big_circ = Circle(2, 2, 3.6);
Circle big_circ( ); }
Circle big_circ;
* * * *

20. Overload Constructors
Date me;
Date you(7,25,49);
Date moon(690628);
You must provide constructors for each.
Prototypes Headers
Date( ); Date::Date()
Date(int, int, int); Date::Date(int, int, int)
Date(long) ; Date::Date(long)

21. Class Implementation: Function Syntax
Example double Circle::setVal(int xx, int yy, double rr)
{ xcenter = xx; ycenter = yy; radius = rr; }
* *

22. Function Call Syntax object.function(arguments);
Example a.setVal( ); b.setVal(3, 2, 6.5); big_circ.setVal(1, 4, 8.3) sm_circ.setVal( ); k.setVal(1, 0, 5.0);
* *

23. Initialize Data Members of a Class
Student iago;
iago.ID = 12345;
double checkAmt;
checkAmt = 54.78;
* *

24. Arrays of Objects Date theDate[4]; creates the objects: theDate[0]

25. Arrays of Objects Function calls: thedate[0].showdata(); or
for(ndx=0; ndx<4; ndx++)
theDate[ndx].showdata();

26. Common Errors missing ; at end of class declaration
including a return type with constructor’s prototype
missing a return type with function prototypes
defining more than one default constructor per class

27. Common Errors missing :: and class name in header
forgetting to include the appropriate header files