Computer Notes - Class II

8/3/2019 Computer Notes - Class II

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Class IIClass II

http://ecomputernotes.com


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ReviewReview

this Pointerthis Pointer

Separation of interface and implementationSeparation of interface and implementation

Constant member functionsConstant member functions



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ProblemProblem

Change the class Student suchChange the class Student suchthat a student is given a rollthat a student is given a roll

number when the object is creatednumber when the object is createdand cannot be changed afterwardsand cannot be changed afterwards



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Student ClassStudent Classclass Student{class Student{

intint rollNorollNo;;

public:public:

Student(intStudent(int aNoaNo););intint getRollNogetRollNo();();

voidvoidsetRollNo(intsetRollNo(int aNoaNo););

};};



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Modified Student ClassModified Student Classclass Student{class Student{

constconst intint rollNorollNo;;

public:public:

Student(intStudent(int aNoaNo););intint getRollNogetRollNo();();

voidvoidsetRollNo(intsetRollNo(int aNoaNo););

};};



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ExampleExample

Student::Student(intStudent::Student(int aRollNoaRollNo))

{{

rollNorollNo == aRollNoaRollNo;;

/*error: cannot modify a/*error: cannot modify a

constant data member*/constant data member*/

}}



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ExampleExamplevoidvoidStudent::SetRollNo(intStudent::SetRollNo(int i)i)

{{

rollNorollNo = i;= i;

/*error: cannot modify a constant/*error: cannot modify a constantdata member*/data member*/

}}



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Member Initializer ListMember Initializer List

A member initializer list is a mechanism toA member initializer list is a mechanism to

initialize data membersinitialize data members

It is given after closing parenthesis ofIt is given after closing parenthesis of

parameter list of constructorparameter list of constructorIn case of more then one member useIn case of more then one member use

comma separated listcomma separated list



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ExampleExampleclass Student{class Student{

const intconst int rollNorollNo;;char *name;char *name;

float GPA;float GPA;

public:public:

Student(intStudent(int aRollNoaRollNo))

:: rollNo(aRollNorollNo(aRollNo), name(Null), GPA(0.0){), name(Null), GPA(0.0){

}}

};};



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Order of InitializationOrder of Initialization

Data member are initialized in order they areData member are initialized in order they are

declareddeclared

Order in member initializer list is not significantOrder in member initializer list is not significant

at allat all



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ExampleExampleclass ABC{class ABC{

intint x;x;

intint y;y;

intint z;z;public:public:

ABC();ABC();};};



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ExampleExampleABC::ABC():y(10),x(y),z(y)ABC::ABC():y(10),x(y),z(y)

{{

}}/*/* x = Junk valuex = Junk value

y = 10y = 10z = 10z = 10 */*/



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constconst ObjectsObjects

Objects can be declared constantObjects can be declared constantwith the use of const keywordwith the use of const keyword

Constant objects cannot changeConstant objects cannot changetheir statetheir state



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ExampleExampleintintmain()main()

{{const Studentconst Student aStudentaStudent;;

return 0;return 0;

}}



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public:public:

intint getRollNogetRollNo(){(){

returnreturn rollNorollNo;;

}}};};



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ExampleExampleintintmain(){main(){

const Studentconst Student aStudentaStudent;;intint a =a = aStudent.getRollNoaStudent.getRollNo();();

//error//error

}}



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constconst ObjectsObjects

constconst objects cannot accessobjects cannot accessnonnon

constconstmember functionmember function

Chances of unintentionalChances of unintentionalmodification are eliminatedmodification are eliminated



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public:public:

intint getRollNo()constgetRollNo()const{{

returnreturn rollNorollNo;;

}}};};



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ExampleExampleintintmain(){main(){

const Studentconst Student aStudentaStudent;;

intint a =a = aStudent.getRollNoaStudent.getRollNo();();

}}



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Constant data membersConstant data members

Make all functions that donMake all functions that dont change the state oft change the state of

the object constantthe object constantThis will enable constant objects to access moreThis will enable constant objects to access more

member functionsmember functions



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Static VariablesStatic Variables

Lifetime of static variable isLifetime of static variable is

throughout the program lifethroughout the program life

If static variables are not explicitlyIf static variables are not explicitly

initialized then they are initialized to 0initialized then they are initialized to 0

of appropriate typeof appropriate type



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ExampleExamplevoid func1(int i){void func1(int i){

static intstatic int staticIntstaticInt = i;= i;cout


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Static Data MemberStatic Data Member

DefinitionDefinition

A variable that is part of a class,A variable that is part of a class,

yet is not part of an object of thatyet is not part of an object of thatclass, is called static data memberclass, is called static data member



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Static Data MemberStatic Data Member

They are shared by all instances ofThey are shared by all instances of

the classthe class

They do not belong to anyThey do not belong to anyparticular instance of a classparticular instance of a class



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Class vs. Instance VariableClass vs. Instance Variable

Student sStudent s11,, s2s2,, s3s3;;

Class Space

s1(rollNo,)

s2(rollNo,)

s3(rollNo,)

Instance VariableClass

Variable


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Static Data Member (Syntax)Static Data Member (Syntax)

Keyword static is used to make aKeyword static is used to make adata member staticdata member static

classclass ClassNameClassName{{

staticstatic DataTypeDataTypeVariableNameVariableName;;

};};http://ecomputernotes.com


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Defining Static Data MemberDefining Static Data Member

Static data member is declaredStatic data member is declared

inside the classinside the class

But they are defined outside theBut they are defined outside the

classclass



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Defining Static Data MemberDefining Static Data Memberclassclass ClassNameClassName{{

staticstatic DataTypeDataTypeVariableNameVariableName;;

};};

DataTypeDataType ClassName::VariableNameClassName::VariableName;;



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Initializing Static Data MemberInitializing Static Data Member

Static data members should beStatic data members should be

initialized once at file scopeinitialized once at file scope

They are initialized at the time ofThey are initialized at the time ofdefinitiondefinition



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private:private:static intstatic int noOfStudentsnoOfStudents;;

public:public:

};};

intint Student::noOfStudentsStudent::noOfStudents = 0;= 0;

/*private static member cannot be accessed/*private static member cannot be accessedoutside the class except foroutside the class except forinitialization*/initialization*/



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Initializing Static Data MemberInitializing Static Data Member

If static data members are notIf static data members are not

explicitly initialized at the time ofexplicitly initialized at the time of

definition then they are initializeddefinition then they are initialized

to 0to 0



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ExampleExampleintint Student::noOfStudentsStudent::noOfStudents;;

is equivalent tois equivalent to

intint Student::noOfStudentsStudent::noOfStudents=0;=0;


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Computer Notes - Class II