object oriented programming (oop) - cs304 power point slides lecture 11

8/13/2019 Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 11

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Object Oriented Programming

(OOP)Lecture No. 11


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Review

this Pointer

Separation of interface and implementation

Constant member functions


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Problem

Change the class Student suchthat a student is given a roll

number when the object iscreated and cannot be changed

afterwards


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Student Class

class Student{

int rollNo;

public:Student(int aNo);

int getRollNo();

void setRollNo(int aNo);

};


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Modified Student Class

class Student{

const int rollNo;

public:Student(int aNo);

int getRollNo();

void setRollNo(int aNo);

};


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Example

Student::Student(int aRollNo)

{

rollNo = aRollNo;/*error: cannot modify a

constant data member*/

}


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Example

void Student::SetRollNo(int i)

{

rollNo = i;/*error: cannot modify a

constant data member*/

}


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Member Initializer List

A member initializer list is a mechanismto initialize data members

It is given after closing parenthesis ofparameter list of constructor

In case of more then one member use

comma separated list


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Example

class Student{

const int rollNo;

char *name;

float GPA;

public:

Student(int aRollNo)

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

}

};


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Order of Initialization

Data member are initialized in order theyare declared

Order in member initializer list is notsignificant at all


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Example

class ABC{

int x;

int y;int z;

public:

ABC();};


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Example

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

{

}

/* x = Junk value

y = 10z = 10 */


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Example

int main()

{

const Student aStudent;

return 0;

}


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Example

int main(){


int a = aStudent.getRollNo();

//error

}


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constObjects

constobjects cannot access

non constmember function

Chances of unintentionalmodification are eliminated


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Example

class Student{

int rollNo;

public:

int getRollNo()const{

return rollNo;

}

};


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Example

int main(){


int a = aStudent.getRollNo();}


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Constant data members

Make all functions that dont change thestate of the object constant

This will enable constant objects to accessmore member functions


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Static Variables

Lifetime of static variable isthroughout the program life

If static variables are not explicitlyinitialized then they are initializedto 0 of appropriate type


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Example

void func1(int i){

static int staticInt = i;

cout


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Static Data Member

Definition

A variable that is part of aclass, yet is not part of anobject of that class, is called

static data member


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Static Data Member

They are shared by allinstances of the class

They do not belong to anyparticular instance of a class


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Class vs. Instance Variable

Student s1, s2, s3;

Class Space

s1(rollNo,)

s2(rollNo,)

s3(rollNo,)

Instance VariableClassVariable


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Static Data Member (Syntax)

Keyword static is used to make adata member static

class ClassName{

static DataType VariableName;

};


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Defining Static Data Member

Static data member is declaredinside the class

But they are defined outside theclass


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Defining Static Data Member

class ClassName{

static DataType VariableName;

};

DataType ClassName::VariableName;


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Initializing Static Data Member

Static data members should beinitialized once at file scope

They are initialized at the timeof definition


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Example

class Student{

private:

static int noOfStudents;

public:

};

int Student::noOfStudents= 0;/*private static member cannot be

accessed outside the class except forinitialization*/


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Initializing Static Data Member

If static data members are notexplicitly initialized at the time

of definition then they areinitialized to 0


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Example

int Student::noOfStudents;

is equivalent to

int Student::noOfStudents=0;

object oriented programming (oop) - cs304 power point slides lecture 11

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