A constructor is a special member function that is called whenever an object of its class is created. It initializes the objects of its class. The constructor has the same name as the class and is automatically called when an object is instantiated. Constructors can be default (taking no parameters) or parameterized (taking parameters). Constructors initialize the data members of objects and can allocate memory dynamically. Copy constructors are used to initialize one object using another object of the same class.

2.  A constructor is a “special” member function whose
task to initialize the objects of its class.
 Its special because Its name is the same as the class
name.
 The constructor is invoked whenever an object of its
associated class is created.
 It is called constructor.

3.  //class with a constructor
Class integer
{
int m,n;
Public:
Integer(void); //constructor declared
……………..
…………..
};
Integer::integer(void) //constructor defined
{
m=0;n=0;
}

4. #include<iostream.h>
Class line
{
Public:
Void setlength(void);
Void getlength(void);
Line();
Private:
Double length;
};

5. Line::line(void)
{
Cout<<“object is being created”;
}
Void line::setlength(void)
{
Double l=getlength();
Cout<<“length”<<l;
}

6. Double line::getlength(void)
{
Cout<<“enter length”;
Cin>>length;
Return length;
}
int main()
{
Line ln;
Ln.setlength();
Return 0;
}

8.  A constructor that accepts no parameters is called
default constructor.
 The default constructor for class A is A::A().
 If no such constructor is defined then the compiler
supplies a default constructor.

9.  They should be declared in the public section
 They are invoked automatically when the object are
created
 They do not have return types ,not even void and there
for and they cannot return value
 We cannot refer to the addresses.

10.  The constructor integer (),defined above initializes the
data members of all the objects to zero
 To initialize the various data elements of different
object and different values are created
 The constructors that can take arguments are called
parameterized constructors.

11.  Class integer
{
Int m,n;
Public:
Integer (int x,int y);
……….
};
Integer::integer(int x,int y);
{
M=x;n=y;
}

12. #include<iostream.h>
Class line
{
Public:
Void setlength(void);
Double getlength(void);
Line(double len)
Private:
Double length;
};

13. Line::line(double len)
{
Cout<<“object is being created,length=“<<len;
}
Void line::setlength(void)
{
Double l;
L=grtlength();
Cout<<“length:”<<l;
}

14. Double line::getlength(void)
{
Cout<<“enter length:”;
Cin>>length;
Return length;
}
Int main()
{
Line line(10.0);
Line .setlength(6.0);
}

15.  Two ways:
 By calling the constructor explicitly
Integer int1=integer(0,100);
The statement create on integer object int 1 and passes
the values 0 and 100
by calling the constructor implicitly
integer int 1 (0,100);

16.  A reference variable has been used as an argument to
the copy constructor. we cannot argument by value to a
copy constructor Integer (integer & i);
 A copy constructor is used to declare and initialize an
object from another object
Integer i2(i1);
the object i2 and the same time initialize to the value of
i1
Integer i2 =i1;

17. #include<iostream.h>
Class code
{
Int id;
Public:
Code()
{}
Code(int a)
{
id=a;
}
Code(code &x)
{Id=x.id;}

18. Void display(void)
{
Cout<<id;
}
};
Int main()
{
Code A(100);
Code B(A);
Code C=A;
Code D;

19. D=A;
cout<<“n id of A:”;
A.display();
cout<<“n id of B:”;
B.display();
cout<<“n id of C:”;
C.display();
cout<<“n id of D:”;
D.display();
Return 0;
}

20.  The constructor can also be used to allocate memory
while creating object
 To allocate the right amount of memory each object ,
the object are not of the same size in the saving
memory
 Allocation of memory to object the construction is use
known as dynamic constructor

21.  The program uses two constructors the first is on
empty constructor to declare on array of string
 The second constructor initialize the length of the
string .space allocated to hold the end of string
character”o”.

22. THANK YOU