Computer Notes - Class

8/3/2019 Computer Notes - Class

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ClassClass

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ClassClass

Class is a tool toClass is a tool to reSmithzereSmithze objectsobjects

Class is a tool for defining a new typeClass is a tool for defining a new type



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ExampleExample

Lion is an objectLion is an object

Student is an objectStudent is an object

Both has some attributes and some behaviorsBoth has some attributes and some behaviors



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UsesUses

The problem becomes easy to understandThe problem becomes easy to understand

Interactions can be easily modeledInteractions can be easily modeled



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Type in C++Type in C++

Mechanism for user defined types areMechanism for user defined types are

StructuresStructures

ClassesClasses

BuiltBuilt--in types are likein types are like intint, float and double, float and doubleUser defined type can beUser defined type can be

Student in student management systemStudent in student management system

Circle in a drawing softwareCircle in a drawing software



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AbstractionAbstraction

Only include details in the system that areOnly include details in the system that are

required for making a functional systemrequired for making a functional system

StudentStudent

NameNameAddressAddress

SiblingSibling

Father BusinessFather Business

Relevant to our problem

Not relevant to our problem



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Defining a New User Defined TypeDefining a New User Defined Type

classclass ClassNameClassName

{{

DataTypeDataType MemberVariableMemberVariable;;

ReturnTypeReturnType MemberFunctionMemberFunction();();

};};

Syntax

Syntax



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ExampleExampleclass Studentclass Student

{{intint rollNorollNo;;

char *name;char *name;

float CGPA;float CGPA;

char *address;char *address;

voidvoidsetName(charsetName(char **newNamenewName););

voidvoidsetRollNo(intsetRollNo(int newRollNonewRollNo););

};};

Member variables

Member

Functions



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Why Member FunctionWhy Member Function

They model the behaviors of an objectThey model the behaviors of an object

Objects can make their data invisibleObjects can make their data invisible

Object remains in consistent stateObject remains in consistent state



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ExampleExample

StudentStudent aStudentaStudent;;

aStudent.rollNoaStudent.rollNo = 514;= 514;

aStudent.rollNoaStudent.rollNo == --514;514; //Error//Error



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Object and ClassObject and Class

Object is an instantiation of a user defined typeObject is an instantiation of a user defined type

or a classor a class



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Declaring class variablesDeclaring class variables

Variables of classes (objects) are declared justVariables of classes (objects) are declared just

like variables of structures and builtlike variables of structures and built--in datain datatypestypes

TypeNameTypeNameVaraibaleNameVaraibaleName;;

intint varvar;;




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Accessing membersAccessing members

Members of an object can be accessed usingMembers of an object can be accessed using

dot operator (.) to access via the variable namedot operator (.) to access via the variable name

arrow operator (arrow operator (-->) to access via a pointer to an>) to access via a pointer to an

objectobject

Member variables and member functions areMember variables and member functions are

accessed in a similar fashionaccessed in a similar fashion



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ExampleExampleclass Student{class Student{

intint rollNorollNo;;voidvoidsetRollNo(intsetRollNo(int

aNoaNo););

};};


aStudent.rollNoaStudent.rollNo;;

Error



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Access specifiersAccess specifiers



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Access specifiersAccess specifiersThere are three access specifiersThere are three access specifiers

publicpublicis used to tell that member can be accessedis used to tell that member can be accessedwhenever you have access to the objectwhenever you have access to the object

privateprivateis used to tell that member can only beis used to tell that member can only be

accessed from a member functionaccessed from a member function

protectedprotectedto be discussed when we coverto be discussed when we cover

inheritanceinheritance



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private:private:char * name;char * name;

intint rollNorollNo;;

public:public:voidvoidsetName(charsetName(char *);*);

voidvoidsetRollNo(intsetRollNo(int););

......

};};

Cannot be accessed outside class

Can be accessed

outside class



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......intint rollNorollNo;;

public:public:

voidvoidsetRollNo(intsetRollNo(int aNoaNo););

};};

intint main(){main(){


aStudent.SetRollNo(1);aStudent.SetRollNo(1);

}}



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Default access specifiersDefault access specifiersWhen no access specifier is mentioned then byWhen no access specifier is mentioned then by

default the member is considered privatedefault the member is considered privatemembermember



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{{

char * name;char * name;

intint RollNoRollNo;;

};};

class Studentclass Student

{{

private:private:



};};



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{{


intint RollNoRollNo;;voidvoidSetName(charSetName(char *);*);

};};


aStudent.SetName(Smith);aStudent.SetName(Smith);

Error


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{{char * name;char * name;


public:public:

voidvoidsetName(charsetName(char *);*);

};};


aStudent.SetName(aStudent.SetName(SmithSmith););


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