Class and Constructor

What is Class?

A class is like a blueprint for an object. It is a user defined data type, which holds its own data members and member functions, which can be accessed and used by creating an instance of that class.

What is Constructor?

A constructor is a member function of a class which initializes objects of a class. In C++, Constructor is automatically called when object(instance of class) create. It is special member function of the class.

How constructors are different from a normal member function?

A constructor is different from normal functions in following ways:

• Constructor has same name as the class itself
• Constructors don’t have return type
• A constructor is automatically called when an object is created.
• If we do not specify a constructor, C++ compiler generates a default constructor for us (expects no parameters and has an empty body).

Note: Class and Constructor name must be same.

//simple code
#include<iostream>
using namespace std;
class Rectangle
{
   private : int length,breadth;
   public :
         Rectangle(){                                    //constructor
                length=breadth=1;
         }
                          Rectangle(int l,int b)                              //function overloading
                                   int area();                                         //accessor
                                    int perimeter();                               //accesor
                        int getLength(){                                  //accessor
                               return length;
                           }
                     void setLength(int l){                                    //mutator
                            length=l;
                            ~Rectangle();                                //destructor
                     }
       Rectangle :: area()
            {
                  return length * breadth;
                }
int Rectangle :: perimeter()
{
return 2* (length + breadth);
}
Rectangle :: Rectangle(int l,int b)
{
length =l;
breadth=b;
}
Rectangle :: ~Rectangle()
{}
}
int main()
{
Rectangle r(10,5);
cout<<r.area();
cout<<r.perimeter();
r.setLength(20);
cout<<r.getLength();
}

Once’s the main function end destructor will automatically call because object is going outside scope.