CS240

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CS-240

• Abstract data Types and Classes
• Dick Steflik

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Abstract Data Type

• Abstraction of a real world object as a
  mathematical entity
• Implementation independent model of the entity
• Emphasis on what not how
• Information Hiding to lower level of complexity
• Preconditions and Postconditions

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Pre and Postconditions

• Preconditions the current state of the object
• ex. The object exists and has a nonzero value
• Postconditions the new state of the object after
  the function has been performed
• ex. The object still exists and has increased in
  value by a factor of ten
• are described for every operation belonging to
  the object

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C Class

• An implementation of an ADT
• A user defined type
• Encapsulation of Data and Function
• Data and its manipulators must always be kept
  together

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Class

• Consists of
• an interface definition (fn.h header file)
• Data definition
• Definition of user interface
• an implementation (fn.cpp code file)
• code for user interface
• code for helper functions
• Could both be in same file but that would defeat
  the purpose of information hiding

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Class Interface Definition

• class statement
• class name
• private section
• data content of the class
• statements ahead of public are private
• private functions are for use of the class not
  the class user
• protected section (for base classes only)
• data content of the base class (more later...)
• public section
• prototype statements for member functions
• publishes the user interface to the class

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Using a class

• Must first instantiate an object of type class
  (ex. throttle fuel_control)
• Tell the object what you want it to do by using
  the . operator (dot operator).
• fuel_control.shut_off() (note specify the object
  and the action you want performed)
• if the object returns a value assign it
• current fuel_control.flow()

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Class Constructors

• Assign initial values to an object
• Never returns a value
• Same name as the class
• Guaranteed to be called (automatic) upon
  instantiation of an object of type class

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Default Constructor

• If no constructor is found
• a default constructor, that does no
  initialization is used when the object is defined
  (only reserves the storage defined in the private
  section)

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Object Initialization

• a single constructor may be used that assigns
  values to all private variables
• The constructor can be overloaded to provide
  flexibility to the user
• each overload must have unique signature
• Good idea to always provide a default constructor
  that assigns some value to all private variables

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Destructors

• Automatically run when an object of type class
  goes out of scope
• use to clean up after the object (return
  dynamically allocated storage to the storage
  management system
• Same name as the class, but preceded by a
• no overloading allowed
• never returns a value
• not needed for statically allocated storage

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Member Functions

• Also known as setters and getters
• provide the class behavior
• you should be a setter function and a getter
  function for each piece of private data (also
  known as state data)

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Time class definition
class Time public Time ( )
/ default constructor / Time (
unsigned H , unsigned M , char AorP )
Time ( unsigned mil) Time (const Time
oTime ) / copy constructor
/ void SetHour(unsigned H )
void SetMinute ( unsigned M)
void Setam_pm) (char C) void
SetMiltime() unsigned GetHour()
unsigned GetMinute() unsigned
Getam_pm () unsigned GetMiltime()
void Display ( ostream out)
private unsigned hours , minutes
char am_pm unsigned
miltime
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Time class implementation
TimeTime() // Constructor for the Time class
// initialize time to midnight hours 0
minutes 0 am_pm A miltime
0 TimeTime ( unsigned H , unsigned M ,
char AorP ) hours H minutes M
am_pm AorP if (am_pm P)
miltime ((hours12)100)minutes else
miltime hours100 minutes
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Time class implementation
Time Time ( unsigned mil) hours mil /
100 if (hours gt 12) hours
hours - 12 am_pm P
else am_pm A minutes mil
100 miltime mil
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Time Class Copy Constructor
TimeTime(const Time oTime) hours
oTime.hours min oTime.min am_pm
oTime.am_pm miltime oHours.miltime
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Inline Member Functions

• If a member function is simple define it inline
  in the class definition (header file) (provide
  the function body ..... inline)
• Compiler recompiles the inline code each time it
  is called and places the code inline (like a C
  macro)
• faster code
• uses more storage
• Functions may also be inlined by using the
  Inline keyword

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namespaces

• using namespace std
• The concept of namespaces was added to C in the
  last release of the specification
• namespaces allow you to assign portions of your
  program to different namspaces, variable names
  are local so they may be reused with in a program
  as long as the uses are in different namespaces
• the namespace std is a little special
• you dont have to specify the .h for all
  standard includes
• include ltiostreamgt