COSC3306: Programming Paradigms Lecture 7: Object-Oriented Programming with C

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COSC3306Programming ParadigmsLecture 7
Object-OrientedProgramming with C

• Haibin Zhu, Ph.D.
• Computer Science
• Nipissing University (C) 2003

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C

• A C program is a collection of functions.
• An object-oriented C program has only one
  function that is not part of a class. It is
  always named main and has a specific structure as
  the following.
• return_data_type main()
• ? ? body of function
• The first element of the main function is a
  returned data type, and anything within the
  braces belongs to function and therefore
  constitute the body of the function.
• A C program uses at least one class an
  application class from which an object is created
  to represent the program itself.

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Object and Class Declarations

• A class declaration has the following syntax
• class class_name
• private ? protected ? public
• definition of stored data
• public ? protected ? private
• definition of member functions

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Three sources for classes

• You can declare and implement your own classes.
  These will always be available to you as source
  code.
• You can use classes that someone else has written
  and given to you. In this case, you have source
  code for such classes or using object code for
  the implementation of the classes.
• You can use classes from the program libraries
  that accompany your C development software. The
  implementation of these classes is typically
  supplied as object code.

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Object and Class Implementations

• After a class is declared, its name can be used
  as a type name to declare variables of that class
  type known as objects or sometimes called
  instances of class. The lifetime of the object is
  determined by the scope and lifetime rules of the
  language. C object can be created in two forms
  as the following.
• Creating Objects using Static Binding.
• Creating Objects using Dynamic Binding.

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To create an object using static binding

• We define a variable whose data type is the class
  from which we want to create an object.
• AppClass s
• Age a

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To create an object using dynamic binding

• To create an object using dynamic binding, we use
  the keyword new, followed by the name of class
  from which the object is to be created and a
  parameter list that matches one of the class
  constructors. The new operator performs three
  things.
• It allocates memory for an object.
• It takes the input parameters and passes then
  into the object constructor.
• It returns a pointer to the memory location of
  the created object.

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Examples

• AppClass s
• s ? new AppClass
• Age a
• a ? new Age
• delete object_name
• delete s

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Member Functions Declarations

• return_data_type FunctionName
  (ParamterDataType1, . . . )
• void shift(int amount)
• bool is_on( ) const

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Member Functions Implementations

• class_name member_name
• Age getChild( )
• int Age getChild( ) return childAge

Ex9-1
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Constant member function

• void throttle flow( ) const
• ?? Precondition shut_off has been called at
  least once to initialize throttle.
• ?? Postcondition The value returned is the
  current flow as a proportion of the
• ?? maximum flow.
• return position ? 6.0 ?? since the throttle
  has six positions
• void throttle is_on( ) const
• ?? Precondition shut_off has been called at
  least once to initialize throttle.
• ?? Postcondition if the throttles flow is
  above 0, then the function returns
• ?? true otherwise it returns false.
• return (flow( ) ?0)

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Accessing Members of Class

•  In general, to tell an object to execute one of
  its member functions, we send a message to the
  object, and the syntax for this function call
  depends on whether you are using the static or
  dynamic bindings as follows
• When the object is created by static binding, we
  use the member access operator as dot operator
  ..
• When the object is created by dynamic binding, we
  use the member access operator as arrow operator
  ??, consisting of a minus (?) sign and a
  greater than (?) sign with no intervening spaces.

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Friend Classes and Functions

•  In the spirit of data encapsulation, the members
  of a class should be kept private so that they
  are not accessible to functions outside of the
  class.
• The C friend mechanism allows the programmer
  to bypass class access restrictions, meaning that
  eliminates data encapsulation.
• For example, consider the following segments of
  code
• class A
• friend class B
• class B
• friend class C

Ex9-2
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Inheritance

• Inheritance is a form of software reusability in
  which new classes are created from existing ones
  by taking their attributes and behavior and
  including those with capabilities the new classes
  require.
•  The declaration of derived classes must include
  the name of the class from which the new class is
  derived and the type of inheritance that is in
  effect. The derived class declaration has the
  following syntax
• class class_nameinheritance_type base_class_name
  

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inheritance_type

• The inheritance_type can be either public,
  protected or private.
• The public and protected members of a base class
  are also public and protected in a public derived
  class.
• The public and protected members of a base class
  are protected in a protected derived class.
• In a private derived class, both the public and
  protected members of the base class are private.

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An example of inheritance

• ?? POINT.H
• ifndef POINT_H
• define POINT_H
• class Point
• friend ostream operator ?? (ostream ,
  const Point )
• public
• Point(float ? 0., float ? 0.) ?? default
  constructor
• void setPoint(float, float) ?? set
  coordinates
• float GetX( ) const return X ?? get
  X coordinate
• float GetY( ) const return Y ?? get
  Y coordinate
• protected ?? accessible by derived classes
• float X, Y ?? X and Y coordinates of Point
  class
• endif

Circlemain.cpp
Ex9-3
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Polymorphism

• The quality of being able to assume different
  forms is called polymorphism.
• C allows you to give two or more different
  definitions to the same function name, which
  means you can reuse names that have strong
  intuitive appeal across a variety of situations.
• In C polymorphism is implemented via virtual
  functions, functions that must be referenced with
  a pointer (using dynamic binding). In other
  words, when a request is made through a
  base-class pointer (or reference) to use a
  virtual function, C chooses the correct
  redefined function in the appropriate derived
  class associated with the object. In this
  respect, the keyword virtual tells C to wait
  until a method is called before deciding which
  definition of that method to use.
• virtual function_type function_name
  (arguments)
• EX9-4, Ex9-5

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Summary

• OOP
• Objects (Abstraction)
• Classes (ADT)
• Inheritances (Classification)
• Overloading (Polymorphism)
• Dynamic Binding (Polymorphism)