Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 07

8/13/2019 Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 07

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Object oriented programming(OOP)

Lecture No. 7


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Class

Class is a tool to realize objects

Class is a tool for defining a new type


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Example

Lion is an object

Student is an object

Both has some attributes and somebehaviors


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Uses

The problem becomes easy to understand

Interactions can be easily modeled


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Type in C++

Mechanism for user defined types are

Structures

Classes

Built-in types are like int, float and double

User defined type can be

Student in student management system Circle in a drawing software


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Abstraction

Only include details in the system that arerequired for making a functional system

Student

Name

Address

Sibling

Father Business

Relevant to our problem

Not relevant to our problem


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Defining a New User Defined Type

class ClassName

{

DataTypeMemberVariable;

ReturnTypeMemberFunction();

};

Syntax

Syntax


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Example

class Student

{

int rollNo;

char *name;

float CGPA;

char *address;

void setName(char *newName);

void setRollNo(int newRollNo);

};

Member variablesMembe

rFunctions


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Why Member Function

They model the behaviors of an object

Objects can make their data invisible

Object remains in consistent state


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Example

Student aStudent;

aStudent.rollNo = 514;

aStudent.rollNo = -514; //Error


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Object and Class

Object is an instantiation of a user definedtype or a class


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Declaring class variables

Variables of classes (objects) are declaredjust like variables of structures and built-indata types

TypeName VaraibaleName;

intvar

;Student aStudent;


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Accessing members

Members of an object can be accessedusing

dot operator (.) to access via the variable name

arrow operator (->) to access via a pointer toan object

Member variables and member functions

are accessed in a similar fashion


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Example

class Student{

int rollNo;

void setRollNo(int

aNo);};

Student aStudent;

aStudent.rollNo;

Error


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Access specifiers


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Access specifiers

There are three access specifiers

public is used to tell that member can beaccessed whenever you have access to the

objectprivate is used to tell that member can only be

accessed from a member function

protected to be discussed when we coverinheritance


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Example

class Student{

private:

char * name;

int rollNo;public:

void setName(char *);

void setRollNo(int);

...

};

Cannot be accessed outside class

Can be

accessed

outside class


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Example

class Student{

...

int rollNo;

public:void setRollNo(int aNo);

};

int main(){

Student aStudent;aStudent.SetRollNo(1);

}


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Default access specifiers

When no access specifier is mentioned thenby default the member is considered privatemember


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Example

class Student

{

char * name;

int RollNo;

};

class Student

{

private:

char * name;

int RollNo;

};


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Example

class Student

{

char * name;int RollNo;

void SetName(char *);

};Student aStudent;

aStudent.SetName(Ali);

Error


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Example

class Student

{

char * name;

int RollNo;public:

void setName(char *);

};Student aStudent;

aStudent.SetName(Ali);

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Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 07

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