classes and objects

1 . STRUCTURE 2 . CLASS 3 . CLASS DECLARATION 4 . CLASS MEMBERS 5 . ARRAY OF OBJECTS 6 . PASSING OBJECTS TO FUNCTION

Classes And Objects

Compiled By: Kamal Acharya

STRUCTURE

It is the collection of different types of data under the common name.

Syntax:

struct StructureName

{

dataType var1;

dataType var2;

………………….;

dataType varN;

};


Example: struct Student

{

int Roll;

char Name[20];

} ;


Declaring Variables

StructureName variableName;

StructureName variableName[10];

Example

Student ram;

Student s[5];


Intialization:

StructureName VariableName ={ val1, val2,.........,valN};

Example:

Student Ram={11,”Ram”};


Processing Structure

#include<iostream.h>

#include<conio.h>

struct student

{

int roll;

char name[20];

};

void main()

{

student s1;

clrscr();

cout<<"Enter Roll Number"<<endl;

cin>>s1.roll;

cout<<"Enter Your Name"<<endl;

cin>>s1.name;

cout<<"Your Name is "<<s1.name<<endl;

cout<<"Your Roll Number is "<<s1.roll;

getch();

}


Output


Passing Structure to Function


#include<conio.h>

struct student

{

int roll;

char name[20];

};

void display(struct student s);

void main()

{

student s1={12,"Sita"};

clrscr();

display(s1);

getch();

}

void display(struct student s1)

{

cout<<"Your Name is "<<s1.name<<endl;

cout<<"Your Roll Number is "<<s1.roll;

}


Output


LIMITATION OF STRUCTURES

Struct data type can’t be treated as the built in type.

Example:

struct complex

{

int real;

int img;

}c1,c2,c3;

c3= c1+c2; //Illegal


Do not permit data hiding. Structure members can be directly accessed by structure variables by any function any where

Example

complex c1;

c1.real= 20;

c1.img=70;


CLASSES

C++ incorporates all the features of structure while avoiding the drawbacks in new user defined data types called Class.

Classes can hold both data and the functions

Classes members are private by default.


Class Declaration

Syntax:

class className

{

private:

variables declaration;

functions declaration;

public:

variables declaration;

functions declaration;

}; Compiled By: Kamal Acharya

Creating Objects

Example

class item

{

int number;

float cost;

public:

void getdata(int a , float b);

void putdata();

} ;

item x; //single object

item x[5]; // array

At the time of definition also we can create objects.

class item

{

………

………..

}x,z[20];


Accessing Class Members

Syntax:

objectName.functionName(arguments);

Example

x.getdata(100,75.5);


Defining Member Function

Member Function can be defined in two places:

1. Inside the Class

Are inline by default.

2. Outside the Class

Syntax:

returnType className::functionName(arguments)

{

function body;

}


Defining member function inside the class

class item

{

int number;

float cost;

public:

void getdata(int a,float b)

{

number=a;

cost=b;

}

void putdata()

{

cout<<number;

cout<<cost;

}

};


Defining member function outside the class

class item

{

int number;

float cost;

public:

void getdata(int a,float b);

void putdata();

};

void item::getdata(int a, float b)

{

number=a;

cost=b;

}

void item::putdata()

{

cout<<number;

cout<<cost;

} Compiled By: Kamal Acharya

C++ program with class


#include<conio.h>

class item

{

int number;

float cost;

public:

void getdata(int a, float b);

void putdata()

{

cout<<"Number:"<<number<<endl;

cout<<"Cost:"<<cost<<endl;

}

};

void item::getdata(int a, float b)

{

number=a;

cost=b;

}

void main()

{

item x;

clrscr();

cout<<"Object x"<<endl;

x.getdata(10,2.9);

x.putdata();

item y;

cout<<"Object y"<<endl;

y.getdata(12,4.7);

y.putdata();

getch();

}


Output


Making Outside Function Inline

Class item

{

……….

public:

…………..

void getdata(int a, float b);

};

inline void item :: getdata(int a, float b)

{

function body;

}


Nesting of member function


#include<conio.h>

class item

{

int n,m;

public:

void getdata(int a, int b);

int largest();

void putdata();

};

void item::getdata(int a, int b)

{

n=a;

m=b;

}

void item::putdata()

{

cout<<"The largest number is " <<largest();

}

int item::largest()

{

if(n>m)

return n;

else

return m;

}

void main()

{

item x;

clrscr();

x.getdata(20,70);

x.putdata();

getch();

}


OUTPUT


Memory Allocation for Objects

• Each objects has its own separate data items and memory are allocated when the objects are created.

• Member function are created and put in the memory only once when class are defined.


Static Data Members

It is initialized to zero when first object is created.

Only one copy is created for entire class.

It is visible within the class but its life time is the entire program.

Type and scope of each static member variable must be defined outside the class definition.

They are stored separately rather than as a part of the object.


Program to show the static data members


#include<conio.h>

class item

{

static int count;

int number;

public:

void getdata(int a)

{

number=a;

count++;

}

void getcount()

{

cout<<"Count: "<<count<<endl;

}

};

int item::count; // REMEMBER THIS

void main()

{

item a,b,c;

clrscr();

cout<<"Before Reading Data" <<endl;

a.getcount();

b.getcount();

c.getcount();

a.getdata(10);

b.getdata(20);

c.getdata(30);

cout<<"After Reading Data" <<endl;

a.getcount();

b.getcount();

c.getcount();

getch();

}


OUTPUT


Static Member Function

It has access to only other static members(function or variables) declared in the same class.

To declare any function static just put the keyword static in front of the function defination.

static returnType functionName(arguments)

{

function body;

}

It can be called using the class name as follows:

className :: functionName(arguments);


Program to show the work of static function


#include<conio.h>

class item

{

static int count;

int code;

public:

void setcode()

{

code=++count;

}

void showcode()

{

cout<<"Object Number: "<<code<<endl;

}

static void showcount()

{

cout<<"Count: "<<count<<endl;

}

};

int item::count;

void main()

{

item t1,t2;

clrscr();

t1.setcode();

t2.setcode();

item::showcount();

item t3;

t3.setcode();

item::showcount();

t1.showcode();

t2.showcode();

t3.showcode();

getch();

}


OUTPUT


Remember It Won’t Work

static void showcount()

{

cout<<code; //code is not static

}


Array of Objects

We can create the array of objects as:

className variable[x];

To access the individual element we have to take the help of the dot operator.

variable[i].function(arguments);


Program to demonstrate the array of objects


#include<conio.h>

class employee

{

char name[30];

int age;

public:

void getdata();

void putdata();

};

void employee::getdata()

{

cout<<"Enter name:"<<endl;

cin>>name;

cout<<"Enter age:"<<endl;

cin>>age;

cout<<endl;

}

void employee::putdata()

{

cout<<"Name: "<<name<<endl;

cout<<"Age: "<<age<<endl;

}

void main()

{

employee manager[2];

int i;

clrscr();

for(i=0;i<2;i++)

{

cout<<"Details of manager"<<i+1<<endl;

manager[i].getdata();

}

cout<<endl;

for(i=0;i<2;i++)

{

cout<<endl<<"Manager"<<i+1<<endl;

manager[i].putdata();

}

getch();

}


OUTPUT


Passing objects to function

Two Ways to pass the objects to the function:

1. Passing by value

Entire object is passed is passed to the function.

2. Passing by reference

Only the reference to the object is passed.


Passing by value


#include<conio.h>

class test

{

int a;

public:

void getdata(int x)

{

a=x;

}

void add(test, test);

};

void test::add(test x, test y)

{

cout<<"The sum of the values is: “ <<x.a+y.a<<endl;

}

void main()

{

test t1,t2,t3;

clrscr();

t1.getdata(40);

t2.getdata(20);

t3.add(t1,t2);

getch();

}


OUTPUT


Passing By Reference


#include<conio.h>

class test

{

int a;

public:

void getdata(int x)

{

a=x;

}

void putdata()

{

cout<<"a= "<<a<<endl;

}

void change(test &, test &);

};

void test::change(test &x, test &y)

{

int temp;

temp=x.a;

x.a=y.a;

y.a=temp;

}

void main()

{

test t1,t2,t3;

clrscr();

t1.getdata(40);

t2.getdata(20);

cout<<"Before Swapping"<<endl;

cout<<"In t1"<<endl;

t1.putdata();


t2.putdata();

t3.change(t1,t2);

cout<<"After Swapping"<<endl;


t1.putdata();


t2.putdata();

getch();

}


OUTPUT


classes and objects

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