Constructors In C ++

What is constructor? Define Constructor with example

Constructor is a special member function of a class. It is used to initialize fo an instance of the class. Constructors are automatically invoked when object is created.  It is different from all other member functions because it is used to initialize the variables of class. 

Rules for writing Constructors:

• Constructor name same as that of class name

• It is declared with no return type. Not even void

• Constructor may not be static and virtual

• It should have public or protected access within the class

General Syntax to declare Constructor:

class class_name

{

private:

__________

__________

protected:

_________

_________

public:

class_name();  // constructor

_________

_________

};

class_name::class_name()

{

___________

____________

}

Following example illustrates constructor inside of class definition

class student

{

private:

char name[20];

int rollno[20];

public:

student() //constructor

{

___________

___________

 }

void display()

{

__________

__________

}

};

Following example illustrates constructor outside of class definition

class student

{

private:

char name[20];

int rollno[20];

public:

student(); // constructor

void getdata();

void display();

};

student::student() //constructor defined outside of class

{

_________

_________ // related methods

}

C ++  program to display Fibonacci series using constructor 

// Display Fibonacci series using constructor

#include<iostream.h>

#include<conio.h>

class fibonacci

{

private:

int f0, f1, f2;

public:

fibonacci() /constructor

{

f0 = 0;

f1 = 1;

f2 = f0 + f1;

}

void  display()

{

f0 = f1;

f1 = f2 ;

f2 = f0+f1;

cout<<” Fibonacci Series is:”<<’\t’;

}

};

void main()

{

fibonacci obj;

// Fibonacci series number up to 50

for(int i=0 ; i<=50; i++)

{

obj.display();

}

}