4%29Operator Overloading %26 Inheritance

8/6/2019 4%29Operator Overloading %26 Inheritance

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C++ ( OOP )OVERLOADING & INHERITACE

Prepared by: Mohamed Farag


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Contents

Operator Overloading Definition

Syntax

Overloading Unary Operators

Overloading Binary Operators

Data Conversion Inheritance

Definition

Base And Derived Classes

Access Specifier(Private ,Protected,public)

Constructor ,Destructor in derived class Private,Protected,Public inheritance

Example

Visual Example

15/3/2011C++ (OOP) CECE Academic Team


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Definition

Operator overloading is one of the most excitingfeatures of object-oriented programming.

In C++ the overloading principle applies not only

to functions, but to operators too.

For example, statements like

d3.addobjects(d1, d2);

d3 = d1.addobjects(d2); can be changed to the much more readable

d3 = d1 + d2;



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Syntax

Operator Overloading is often similar toOverloading a Function Using operator Keywordfollowed by the operator we want to overload.

Return Type Operator Operator_sign (Args)

{

}



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Unary operators is that operators which act on only one operand like(++,--,Minus -)

EX:-

Class Counter

{

private:

unsigned int count; //count

public:

Counter() : count(0) //constructor

{ }

unsigned int get_count() //return count

{ return count; }

void operator ++ () //increment (prefix) {

++count;

}

};



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int main()

{

Counter c1; //define and initialize

cout


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Overloading Return Value:-

EX: -

Counter operator ++ () //increment count

{

++count; //increment count

Counter temp; //make a temporary Counter

temp.count = count; //give it same value as this obj return temp; //return the copy

}



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Nameless Temporary Objects:-

Ex:-

Counter operator ++ () //increment count

{

++count; // increment count, then return

return Counter(count); // an unnamed temporary object

} // initialized to this count



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Binary operators can be overloaded just as easily asunary operators .Arithmatic operators, comparisonoperators, and arithmetic assignment operators.

Ex:- Distance Addition

Distance operator +(Distance C)

{ Meters+=C.Meters;

CMs+=C.CMs;

If(CMs>=100)

{Meters++;CMs-=100;}

Return *this;//this is a pointer to the created object itself

}



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Ex:- Distance Comparison

bool operator


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Ex:- Arithmetic Assignment Operator

void operator += (Distance C)

{

Meters+= C.Meters; //add the Meters

CMs += C.CMs; //add the CMs

if(CMs >= 100) //if total exceeds 100,

{ //then decrease CMs

CMs -= 100; //by 100 and

Meters++; //increase Meters by 1

}

}



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Data Conversion

Basic Type Data Conversion:- Ex:-

Int x=5;

float y=x; ///or float y = float(x); or y=static_cast=x;

Conversion Between Basic Types and Objects:- Ex:-

Operator float()

{ float x=Meters+CMs/100; return x;

}



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Exercise

Write a program that uses += operator for the overloadedfor concatenation and should allow statements like

s1 += s2;

where s2 is added (concatenated) to s1 and the result is left ins1.

The operator should also permit the results of the operation tobe used in other calculations, as in

s3 = s1 += s2;



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Solution


class String //user-defined string type

{

private:

enum { SZ = 80 }; //size of String objects

char str[SZ]; //holds a C-string

public:

String() //no-arg constructor

{ strcpy(str, ); }

String( char s[] ) //1-arg constructor

{ strcpy(str, s); }

void display() //display the String { cout


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Break :D



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Inheritance

Definition


Access Specifier(Private ,Protected,public)

Constructor ,Destructor in derived class

Private,Protected,Public inheritance

Example

Visual Example



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Definition

Inheritance is probably the most powerful feature of

object-oriented programming, after classes

themselves.

Inheritance is a mechanism of reusing and extendingexisting classes without modifying them, thus

producing hierarchical relationships between them.

Its big payoff is that it permits code reusability

Inheritance can also help in the original

conceptualization of a programming problem, and in

the overall design of the program.



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Example

Rem:Counter Example in Operator Overloading

class Counter //base class(Parent)

{

protected: //NOTE: not private

unsigned int count; //count

public: Counter() : count(0) //no-arg constructor

{ }

Counter(int c) : count(c) //1-arg constructor

{ }

unsigned int get_count() const //return count

{ return count; } Counter operator ++ () //incr count (prefix)

{ return Counter(++count); }

};



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Example


class CountDn : public Counter //derived class(Child)

//setup the relationship between Counter and CountDn

{

public: Counter operator -- () //decr count (prefix)

{ return Counter(--count); } //unnamed Temp Class

};

Note : Members of Derived class can't access members of baseclass Unless they are public or protected


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Example(Access specifiers)



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Constructor and Destructor in Derived Class


We knew that the constructor is called by defaultwhen you Declare an Object

If this Object declared from a derived class,then the

constructor of the base class must be called too orthe Data member must be initilized ,so

What is the solution????


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Constructor and Destructor in Derived Class


The solution is to invoke its direct base class'sconstructor either

explicitly (via a base-class member initializer) or

implicitly (calling the base class's defaultconstructor)


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Private , Protected, Public inheritance


Base-class member

access specifier

Type of inheritance

( derived class access )

Derived class member

Public Private Private

Protected Private Private

Private Private Inaccessible

Public Protected Protected

Protected Protected Protected

Private Protected InaccessiblePublic Public Public

Protected Public Protected

Private Public Inaccessible


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Visual Example


Counter Example

Accessing Base Class Members

Substituting Base Class Constructors

Substituting Base Class Member Functions Derived Class Constructors

Overriding Member Functions


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Steps for writing a Program


1. File->new->Project->win32->win32 console

application

2. Write project name->OK->next

3. Choose console application-uncheck Precompiled

4. Check empty project->ok

5. You will find the solution explorer like

That in the picture on the left hand side.


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Steps for Writing a program


To add header files and Source files Right click on header files->add->new

Write class name then choose header file (.h)

Note:the structure of header file

#ifndef CLASSNAME_H

#define CLASSNAME_H

Class Classname

{ };

#endif


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Steps for Writing a program


To add Source Files(.cpp) Right click on source files->add->new item

Write the name of cpp file

Choose C++ FILE(.cpp)

Note:- Each header file has a .CPP file for writing the

implementation of the Function in a separate file. Dont forget to include the class in the main cpp file.

Dont forget to include the Base Class in Derived Classes .


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Exercise


In counter Example, It can increment or decrement a

counter, but only using prefix notation.

Using inheritance, add the ability to use postfix

notation for both incrementing and decrementing.


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References

WWW.CProgramming.com

Object-Oriented Programming in C++ by Lafore

Email:[email protected]

http://www.cprogramming.com/http://www.cprogramming.com/


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THANK YOU!

P d b M h d F13/3/2011

C++ (OOP) CECE Academic Team

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4%29Operator Overloading %26 Inheritance