Mca 2nd sem u-2 classes & objects

UNIT-2
Classes and Object, Dynamic
Memory Management,
Constructor & Destructor
MCA-2nd
Sem

Member Functions
 The program defines person as a new data of type
class.
 The class person include two basic data type items
and two function to operate on that data. it’s call
Member function.
 There are two type:
1 Outside the class definition
2 Inside the class definition

Outside the class Defination
 The member functions of a class can be defied outside
the class definitions. It is only declared inside the class
but defined outside the class. The general form of
member function definition outside the class definition
is:
 Return_typeClass_name::function_name(argumentlist)
{
Functionbody
}
 Where symbol :: is a supe resolution operator.

Inside the class definition
 The member function of a class can be
declared and defined inside the class
definition.
EX.
Class item
{
int number;
float cost;

Inside the class definition
Public:
Void getdata(int a, float b);
Void putdata(void)
{
cout<< number<<“n”;
cout<<cost<<“n”;
}
};

Data Member
 Data member depends on access control of data
member.
 If it’s public then data member can be easily accessed
using the direct member access operator with the
object of that class.
 If the data member is defined as private or protected
then we can not access the data variables directly.

Data Member
Type of data Member
1.Public
2.Private
3.protected

Data member type
#include <iostream>
using namespace std;
class alpha{
private:
int id;
static int count;
public:
alpha(){count++;
id=count;}}

Data member type
void print(){
cout<<"My id is"<<id;
cout<<"countis"<<count;} };
int alpha : :count=0;
void main (){
alpha a1,a2,a3;
a1.print();
a2.print();
a3.print();}

Friend Function
 A friend function of a class is defined outside that
class' scope but it has the right to access all private
and protected members of the class.
 Even though the prototypes for friend functions
appear in the class definition, friends are not member
functions.

Friend Function
Example:
class Box
{
double width;
public: double length;
friend void printWidth( Box box );
voidsetWidth(doublewid);
};

Friend Function Property
1) Friend of the class can be member of some other
class.
2) Friend of one class can be friend of another class or
all the classes in one program, such a friend is
known as GLOBAL FRIEND.
3) Friend can access the private or protected members
of the class in which they are declared to be friend,
but they can use the members for a specific object.

Friend Function Property
4) Friends are non-members hence do not get “this”
pointer.
5) Friends, can be friend of more than one class, hence
they can be used for message passing between the
classes.
6) Friend can be declared anywhere (in public,
protected or private section) in the class.

Friend Class
 A class can also be declared to be the friend of some
other class.
 When we create a friend class then all the member
functions of the friend class also become the friend of
the other class.
 This requires the condition that the friend becoming
class must be first declared or defined (forward
declaration).

Friend Class Example
#include <iostream>
class MyClass{
friend class SecondClass;
public: MyClass() : Secret(0){}
void printMember()
{ cout << Secret << endl;}
private: int Secret; };
}

Friend Class Example
class SecondClass{
public: void change( MyClass& yourclass, int x ){
yourclass.Secret = x;} };
void main()
{
MyClass my_class;
SecondClass sec_class;
my_class.printMember();
sec_class.change( my_class, 5 );
my_class.printMember();}

Array of object
class A
{
int* myArray;
A()
{
myArray = 0;
}
A(int size)
{

Array of object
myArray = new int[size];
}
~A()
{
delete []
myArray;
}
}

Returning Objects from
Functions
#include <iostream>
class Complex{
private: int real;
int imag;
public: Complex():
real(0), imag(0){ }
void Read() {

Returning Objects from Functions
cout<<"Enter real and imaginary number
respectively:"<<endl;
cin>>real>>imag;
}
Complex Add(Complex comp2)
{
Complex temp;
temp.real=real+comp2.real;
temp.imag=imag+comp2.imag;
return temp;

}
void Display()
{
cout<<"Sum="<<real<<"+"<<imag<<"i";
}
};
int main()
{

Complex c1,c2,c3;
c1.Read();
c2.Read();
c3=c1.Add(c2);
c3.Display();
return 0; }

Nested Classes
A class can be declared within the scope of another
class. Such a class is called a "nested class.
" Nested classes are considered to be within the scope
of the enclosing class and are available for use within
that scope.
 To refer to a nested class from a scope other than its
immediate enclosing scope, you must use a fully
qualified name.

Nested Classes Example
#include <iostream.h>
class Nest
{
public: class Display
{
private: int s;
public:
void sum( int a, int b)
{

Nested Classes Example
s =a+b; }
void show( )
{
cout << "nSum of a and b is:: " << s;
} };
};
void main() {
Nest::Display x; x.sum(12, 10);
x.show();
}

Namespaces
 Namespace is a new concept introduced by the ANSI
C++ standards committee.
 This defines a scope for the identifiers that are used in
a program.
 For using the identifier defined in the namespace
scope we must include the using directive, like
 Using namespace std;

Namespaces
 Here, std is the namespace where ANSI C++ standard
class libraries are defined.
 All ANSI C++ programs must include this directive.
 This will bring all the identifiers defined in std to the
current global scope. Using and namespace are the
new keyword of C++.

Constructor
 A constructor (having the same name as that of the
class) is a member function which is automatically
used to initialize the objects of the class type with
legal initial values.

Characteristics of Constructor
(i) These are called automatically when the objects are
created.
(ii) All objects of the class having a constructor are
initialized before some use.
(iii) These should be declared in the public section for
availability to all the functions.

(iv) Return type (not even void) cannot be specified for
constructors.
(v) These cannot be inherited, but a derived class can
call the base class constructor.
(vi) These cannot be static.

(x) An object of a class with a constructor cannot be
used as a member of a union.
(xi) A constructor can call member functions of its
class.
(xii) We can use a constructor to create new objects of
its class type by using the syntax

(vii) Default and copy constructors are generated by the
compiler wherever required. Generated constructors
are public.
(viii) These can have default arguments as other C++
functions.
(ix) A constructor can call member functions of its
class.

Types of Constructor
1 Overloaded Constructors
2 Copy Constructor
3 Dynamic Initialization of Objects
4 Constructors and Primitive Types
5 Constructor with Default Arguments

1.Overloaded Constructors
 Besides performing the role of member data
initialization, constructors are no different from other
functions.
 This included overloading also. In fact, it is very
common to find overloaded constructors.
 For example, consider the following program with
overloaded constructors for the figure class :

#include<iostream.h>
#include<conio.h>
#include<math.h>
#include<string.h> //for strcpy()
Class figure
{
Private:
Float radius, side1,side2,side3;

Figure (float s1, floats2, float s3)
{
ide1=s1;
side2=s2;
side3=s3;
radius=0.0;
strcpy(shape,”triangle”);
}
Char shape[10];
Public:
figure(float r)

{
radius=r;
strcpy (shape, “circle”);
}
void area()
{
float ar,s;
if(radius==0.0)
{
a

if (side3==0.0)
ar=side1*side2;
else
ar=3.14*radius*radius;
cout<<”nnArea of the
“<<shape<<”is :”<<ar<<”sq.unitsn”;
} };
Void main()
{
Clrscr();

Figure circle(10.0); /
Figure rectangle15.0,20.6);
Figure Triangle(3.0, 4.0, 5.0);
Rectangle.area();
Triangle.area();
Getch();//freeze the monitror
}

2.Copy Constructor
 It is of the form classname (classname &) and used
for the initialization of an object form another object
of same type. For example,

2.Copy Constructor
Class fun {
Float x,y;
Public:
Fun (floata,float b)
{
x = a;
y = b;
}
Fun (fun &f)
{

2.Copy Constructor
cout<<”ncopy constructor at workn”;
X = f.x;
Y = f.y;
}
Void display (void)
{
{
Cout<<””<<y<<end1;
}
};

3.Dynamic Initialization of Objects
 The class objects can be initialized at run time
(dynamically).
 We have the flexibility of providing initial values at
execution time.

#include <iostream.h>
#include <conio.h>
Class employee {
Int empl_no;
Float salary;
Public:
Employee() {}
Employee(int empno,float s) {
Empl_no=empno;
Salary=s; }

Employee (employee &emp)
{
Cout<<”ncopy constructor workingn”;
Empl_no=emp.empl_no;
Salary=emp.salary;
}
Void display (void)
{
Cout<<”nEmp.No:”<<empl_no<<”salary:”<<salary<<
end1; }

3.Dynamic Initialization of
Objects
};
Void main()
{ int eno;
float sal;
clrscr();
cout<<”Enter the employee number and salaryn”;
cin>>eno>>sal;
employee obj1(eno,sal);

cout<<”nEnter the employee number and salaryn”;
cin>eno>>sal;
employee obj2(eno,sal);
obj1.display();
employee obj3=obj2;
obj3.display();
getch();
}

4.Constructors and Primitive Types
 In C++, like derived type, i.e. class, primitive types
(fundamental types) also have their constructors.
 Default constructor is used when no values are given
but when we given initial values, the initialization
take place for newly created instance.
 Example:
 float x,y;
 int a(10), b(20);
 float i(2.5), j(7.8);

4.Constructors and Primitive Types
Class add
{
Private:
Int num1, num2,num3;
Public:
Add(int=0,int=0);
Void enter (int,int);
Void sum();
Void display();
};

4.Constructor with Default Arguments
add::add(int n1, int n2)
{
num1=n1;
num2=n2;
num3=n0; }
Void add ::sum()
{
Num3=num1+num2;
}
Void add::display () {
Cout<<”nThe sum of two numbers is “<<num3<<end1;
}

Destructor
 The syntax for declaring a destructor is :
-name_of_the_class()
{
}
 It does not take any parameter nor does it return any
value. Overloading a destructor is not possible and
can be explicitly invoked. I
 n other words, a class can have only one destructor. A
destructor can be defined outside the class. The
following program illustrates this concept :

Destructor
#include<iostream.h>
#include<conio.h>
class add {
private :
int num1,num2,num3;
public :
add(int=0, int=0);
void sum();
void display();
~ add(void); };

Destructor
Add:: ~add(void)
{
Num1=num2=num3=0;
Cout<<”nAfter the final execution, me, the object has
entered in the”
<<”ndestructor to destroy myselfn”;
}
Add::add(int n1,int n2)
{
num1=n1;
num2=n2;
num3=0;
}

Destructor
Void add::sum() {
num3=num1+num2;
}
Void add::display () {
Cout<<”nThe sum of two numbers is “<<num3<<end1;
}
void main()
{

Destructor
Addobj1,obj2(5),obj3(10,20):
Obj1.sum();
Obj2.sum();
Obj3.sum();
cout<<”nUsing obj1 n”;
obj1.display();
obj2.display();
obj3.display();
}

Characteristics of Destructors
(i) These are called automatically when the objects are
destroyed.
(ii) Destructor functions follow the usual access rules
as other member functions.
(iii) These de-initialize each object before the object
goes out of scope.
(iv) No argument and return type (even void) permitted
with destructors.

Characteristics of Destructors
(v) These cannot be inherited.
(vi) Static destructors are not allowed.
(vii) Address of a destructor cannot be taken.
(viii) A destructor can call member functions of its
class.
(ix) An object of a class having a destructor cannot be a
member of a union.

REFRENCES
• Learn Programming in C++ By Anshuman
Sharma, Anurag Gupta, Dr.Hardeep Singh,
Vikram Sharma

Mca 2nd sem u-2 classes & objects

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Mca 2nd sem u-2 classes & objects