Computer Notes - Functions & Constructor

8/3/2019 Computer Notes - Functions & Constructor

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Functions & ConstructorFunctions & Constructor

http://ecomputernotes.com


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ReviewReview

ClassClass

ConceptConcept

DefinitionDefinition

Data membersData membersMember FunctionsMember Functions

Access specifierAccess specifier



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Member FunctionsMember Functions

Member functions are the functions that operateMember functions are the functions that operate

on the data encapsulated in the classon the data encapsulated in the class

Public member functions are the interface to thePublic member functions are the interface to the

classclass



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Member Functions (contd.)Member Functions (contd.)

Define member function inside the classDefine member function inside the class

definitiondefinition

OROR

Define member function outside the classDefine member function outside the classdefinitiondefinition

But they must be declared inside class definitionBut they must be declared inside class definition



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Function Inside Class BodyFunction Inside Class Body

classclass ClassNameClassName {{

public:public:

ReturnTypeReturnType FunctionNameFunctionName() {() {

}}};};



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ExampleExample

Define a class of student that hasDefine a class of student that hasa roll number. This class shoulda roll number. This class should

have a function that can be usedhave a function that can be usedto set the roll numberto set the roll number



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ExampleExampleclass Student{class Student{

intint rollNorollNo;;

public:public:

voidvoidsetRollNo(intsetRollNo(int aRollNoaRollNo){){rollNorollNo == aRollNoaRollNo;;

}}

};};



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Function Outside Class BodyFunction Outside Class Bodyclassclass ClassNameClassName{{

public:public:

ReturnTypeReturnType FunctionNameFunctionName();();

};};

ReturnTypeReturnType ClassNameClassName::::FunctionNameFunctionName()()

{{

}}Scope resolution

operator


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intint rollNorollNo;;

public:public:

voidvoidsetRollNo(intsetRollNo(int aRollNoaRollNo););};};

voidvoidStudent::setRollNo(intStudent::setRollNo(int aRollNoaRollNo){){

rollNorollNo == aRollNoaRollNo;;

}}



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Inline FunctionsInline Functions

Instead of calling an inline function compilerInstead of calling an inline function compiler

replaces the code at the function call pointreplaces the code at the function call point

KeywordKeywordinlineinlineis used to request compiler tois used to request compiler to

make a function inlinemake a function inlineIt is a request and not a commandIt is a request and not a command



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ExampleExampleinlineinline intintArea(intArea(int lenlen,, intint hi)hi)

{{returnreturn lenlen * hi;* hi;

}}

intintmain()main()

{{

coutcout


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Inline FunctionsInline Functions

If we define the function inside the class bodyIf we define the function inside the class body

then the function is by default an inline functionthen the function is by default an inline function

In case function is defined outside the classIn case function is defined outside the class

body then we must use the keywordbody then we must use the keywordinlineinlinetotomake a function inlinemake a function inline



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intint rollNorollNo;;public:public:

voidvoid

setRollNo(intsetRollNo(int

aRollNoaRollNo

){){


}}};};



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public:public:

inline voidinline voidsetRollNo(intsetRollNo(int aRollNoaRollNo););

};};

voidvoidStudent::setRollNo(intStudent::setRollNo(int aRollNoaRollNo){){


}}



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public:public:

voidvoidsetRollNo(intsetRollNo(int aRollNoaRollNo););

};};inline voidinline voidStudent::setRollNo(intStudent::setRollNo(int

aRollNoaRollNo){){


}}



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public:public:

inline voidinline voidsetRollNo(intsetRollNo(int aRollNoaRollNo););

};};inline voidinline voidStudent::setRollNo(intStudent::setRollNo(int

aRollNoaRollNo){){


}}



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ConstructorConstructor



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ConstructorConstructorConstructor is used to initialize the objects of aConstructor is used to initialize the objects of a

classclassConstructor is used to ensure that object is inConstructor is used to ensure that object is in

well defined state at the time of creationwell defined state at the time of creation

Constructor is automatically called when theConstructor is automatically called when the

object is createdobject is created

Constructor are not usually called explicitlyConstructor are not usually called explicitly



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Constructor (contd.)Constructor (contd.)Constructor is a special function having sameConstructor is a special function having same

name as the class namename as the class nameConstructor does not have return typeConstructor does not have return type

Constructors are commonly public membersConstructors are commonly public members



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public:public:

Student(){Student(){

rollNorollNo = 0;= 0;

}}};};



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ExampleExampleintintmain()main()

{{

StudentStudent aStudentaStudent;;

/*constructor is implicitly called/*constructor is implicitly calledat this point*/at this point*/

}}



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Default ConstructorDefault ConstructorConstructor without any argument is calledConstructor without any argument is called

default constructordefault constructorIf we do not define a default constructor theIf we do not define a default constructor the

compiler will generate a default constructorcompiler will generate a default constructor

This compiler generated default constructorThis compiler generated default constructor

initialize the data members to their defaultinitialize the data members to their default

valuesvalues



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ExampleExampleclass Studentclass Student

{{intint rollNorollNo;;

char *name;char *name;

float GPA;float GPA;

public:public:

//no constructors//no constructors};};



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ExampleExample

Compiler generated default constructorCompiler generated default constructor

{{


GPA = 0.0;GPA = 0.0;

name = NULL;name = NULL;

}}



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Constructor OverloadingConstructor OverloadingConstructors can have parametersConstructors can have parameters

These parameters are used to initialize the dataThese parameters are used to initialize the datamembers with user supplied datamembers with user supplied data



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public:public:

Student();Student();

Student(char *Student(char * aNameaName););Student(char *Student(char * aNameaName,, intint aRollNoaRollNo););

Student(intStudent(int aRollNoaRollNo,, intint aRollNoaRollNo, float, float

aGPAaGPA););};};



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ExampleExampleStudent::Student(Student::Student(intint aRollNoaRollNo,,

char *char * aNameaName){){if(aRollNoif(aRollNo< 0){< 0){


}}else {else {


}}

}}



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ExampleExampleintintmain()main()

{{

Student student1;Student student1;

Student student2(Student student2(NameName););Student student3(Student student3(NameName, 1);, 1);

Student student4(Student student4(NameName,1,4.0);,1,4.0);

}}



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Constructor OverloadingConstructor OverloadingUse default parameter value to reduce theUse default parameter value to reduce the

writing effortwriting effort



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ExampleExampleStudent::Student(Student::Student( char *char * aNameaName = NULL,= NULL,

intint aRollNoaRollNo= 0,= 0,

floatfloat aGPAaGPA= 0.0){= 0.0){

}}

Is equivalent toIs equivalent toStudent();Student();

Student(char *Student(char * aNameaName););

Student(char *Student(char * aNameaName,, intint aRollNoaRollNo););Student(char * Name,Student(char * Name, intint aRollNoaRollNo, float, float aGPAaGPA););



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Copy ConstructorCopy ConstructorCopy constructor are used when:Copy constructor are used when:

Initializing an object at the time of creationInitializing an object at the time of creation

When an object is passed by value to a functionWhen an object is passed by value to a function



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ExampleExamplevoid func1(Student student){void func1(Student student){

}}

intintmain(){main(){

StudentStudent studentAstudentA;;

StudentStudent studentBstudentB == studentAstudentA;;

func1(studentA);func1(studentA);}}



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Copy Constructor (Syntax)Copy Constructor (Syntax)Student::Student(Student::Student(

const Student &const Student &objobj){){rollNorollNo == obj.rollNoobj.rollNo;;

name =name = obj.nameobj.name;;

GPA =GPA = obj.GPAobj.GPA;;

}}



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Shallow CopyShallow CopyWhen we initialize one object with another thenWhen we initialize one object with another then

the compiler copies state of one object to thethe compiler copies state of one object to theotherother

This kind of copying is called shallow copyingThis kind of copying is called shallow copying



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ExampleExample

Student studentA;

Student studentB = studentA;

Name

GPA

RollNo

studentA

Name

GPA

RollNo

studentBA

H

M

AD

Memory


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Copy Constructor (contd.)Copy Constructor (contd.)Student::Student(Student::Student(

const Student &const Student & objobj){){intint lenlen == strlen(obj.namestrlen(obj.name););

name = new char[len+1]name = new char[len+1]

strcpy(namestrcpy(name,, obj.nameobj.name););

//copy rest of the data members//copy rest of the data members

}}



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Copy Constructor (contd.)Copy Constructor (contd.)Copy constructor is normally used to performCopy constructor is normally used to perform

deep copydeep copyIf we do not make a copy constructor then theIf we do not make a copy constructor then the

compiler performs shallow copycompiler performs shallow copy



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ExampleExample

Name

GPARollNo

A

Name

GPARollNo

B

AH

M

AD

Memory

A

HM

A

D

Student studentA;Student studentB = studentA;

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Computer Notes - Functions & Constructor