More about OOP and ADTs Classes

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More about OOP and ADTsClasses

• Chapter 4

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Chapter Contents

• 4.1 Procedural vs. Object-Oriented Programming
• 4.2 Classes
• 4.3 Example a First Version of Complex Class
• 4.4 Class Constructors
• 4.5 Other Class Operators

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Contrast Procedural, Object Oriented Paradigms

• Procedural
• Action-oriented concentrates on the verbs
• Programmers
• Identify basic tasks to solve problem
• Implement actions to do tasks as subprograms
  (procedures/functions/subroutines)
• Group subprograms into programs/modules/libraries,
  
• together make up a complete system for solving
  the problem

• Object-oriented
• Focuses on the nouns of problem specification
• Programmers
• Determine objects needed for problem
• Determine how they should work together to solve
  the problem.
• Create types called classes made up of
• data members
• function members to operate on the data.
• Instances of a type (class) called objects.

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Structs and Classes Similarities

• Essentially the same syntax
• Both are used to model objects with multiple
  attributes (characteristics)
• represented as data members
• also called data fields or attribute members
• Thus, both are used to process non-homogeneous
  data sets.

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Structs vs. Classes

• No classes in C
• Members public by default
• Can be specified private

• Both structs and classes in C
• Structs can have members declared private
• Class members are private by default
• Can be specified public

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Advantages in C(structs and Classes)

• C structs and classes model objects which have
• Attributes represented as data members
• Operations represented as functions (or methods)
• Leads to object oriented programming
• Objects are self contained
• "I can do it myself" mentality
• They do not pass a parameter to an external
  function (operate on them)

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Class Declaration

• Syntaxclass ClassName public
  Declarations of public members private
  Declarations of private members

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Designing a Class

• Data members normally placed in private section
  of a class
• the private members are accessible only by the
  member functions or friend functions
• Function members usually in public section
• the public members are accessible by any
  external members

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A declaration for a complex class

• class Complex
• private
• float real, imag
• public
• void assignReal(float)
• void assignImag(float)
• float getReal()
• float getImag()
• Complex add(Complex)
• Complex subtract(Complex)
• Complex multiply(Complex)
• Complex divide(Complex)

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Complex Class

• Note interface for Complex class object,
• Data members private inaccessible to users of
  the class
• Information hiding, Implementation details are
  hided to users of the class

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Class Libraries

• Class declarations placed in header file
• Given .h extension
• Contains data items and function prototypes
• Implementation file
• Same prefix name as header file
• Given .cpp extension
• Programs which use this class library called
  client programs

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Translating a Library
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Member functions in class (1)

• Ordinary member functions
• ordinary functions defined with a return type
  (or void) and parameters
• Constructors
• Have the same name as the class
• Do not return any values
• Are invoked when an object of the class is
  declared and memory allocation is done at the
  constructor
• There can be any number of overloaded
  constructors in a class (different sets of
  parameters)

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Member functions in class (2)

• Destructors
• Have the same name as the class
• They are preceded by a operator
• Are invoked when the object of a class goes out
  of scope

If a constructor/destructor is not declared, the
compiler will automatically create a default one
for each. If we dont need to initialize any data
members to point to dynamically allocated memory
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An member function implementation

• The implementation of the assignReal() member
  function would appear in the definition file as
• void ComplexassignReal(float re) real re
• The double colon operator used in this
  definition is the scope resolution operator.

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Inline function

• Problem
• the function call overhead may actually
  consume more time than the operations the
  functions are performing.
• Solution Inline function
• An inline function is declared by placing the
  keyword inline in front of the function
  declaration and definition.
• If a function is declared inline, the compiler
  attempts to replace every call of that function
  with a copy of the entire function.

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Inline function

• the assignReal() member function could be
  rewritten by placing the following definition in
  the header file for the complex class
• inline void Complexassign_real(float re) real
  re

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Inline function

• class Complex
• private
• float real, imag
• public
• inline void assignReal(float re) real re
• inline void assignImag(float im) imag im
• inline float getReal() return real
• inline float getImag() return imag
• // remaining members functions not shown
•  

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Variable declaration and others
Complex Complexadd (Complex) return
Complex(real num3.real, imag num3.imag)

• Variables of type Complex can now be declared
• Complex num1, num2, num3
• creates three objects of type Complex called
  num1, num2, and num3.
• These objects may be operated on by invoking
  their member functions.
• num1.assignReal(3.2)
• this statement uses the assignReal() member
  function to assign the value 3.2 to the member
  variable real.
• num1 num2.add(num3)
• This adds the complex numbers represented by num2
  and num3, and assigns the result to num1.

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Constructors

• Constructor specify what should happen when a new
  object is created.
• It is invoked when a class object is declared, or
  when a class object is dynamically allocated
  using the new operator
• SyntaxClassNameClassName (parameter_list)
  member_initializer_list // body of constructor
  definition

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Add Constructor in class

• class Complex
• private
• float real, imag
• public
• Complex() //default constructor
• Complex(float re,float im)
• //a constructor with initial value
• // remaining member functions not shown

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Constructor Definition

• ComplexComplex() //default constructor
• real(0), imag(0)
• ComplexComplex(float re, float im)
• realre
• imagim

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Constructor

• Constructor can be called as below.
• Complex num1 // num1.real0.0,num1.imag0.0
• Complex num2(3.2) // num2.real3.2 num2.imag0.0
• Complex num3(5.1,2.7)/num3.real5.1,
  num3.imag2.7/
• three objects of type Complex are declared and
  initialized differently depending upon how the
  constructor is called.
• (this is also an example of function overloading)

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Constructor

• If no constructor is given in a class, compiler
  will provide a default constructor, memory will
  still be allocated for each data member of an
  object by compiler (not dynamic allocation)

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Overloading Functions

• Note existence of multiple functions with the
  same nameComplex()
• Complex(float re,float im)
• Known as function overloading
• Compiler compares numbers and types of arguments
  of overloaded functions
• Checks the "signature" of the functions

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Friend Functions

• If a function declaration in a class is preceded
  by the keyword friend, then that function is said
  to be a friend of the class.
• A friend function is not an actual member of the
  class however, it is still permitted to access
  the private data members of the class.

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Friend Functions

• Note - a friend function not member function
• not qualified with class name and
• Since they are not members of any class, you
  should not call them using the dot operator.

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Pointers to Class Objects

• Possible to declare pointers to class
  objectsComplex Ptr x
• Access with Ptr-gtgetReal() or
  (Ptr).getReal()

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The this Pointer

• Every class has a keyword, this
• a pointer whose value is the address of the
  object
• Value of this would be the object itself

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The this Pointer example

• Complex Complexoperator(const Complex z)
• real z.real
• imag z.imag
• return this
• Invoke the function
• Complex c1(1.1,2.2), c2
• c2 c1