What is copy constructor?

Question

We define copy constructor using
A(const A & obj)

Why reference (&) is needed?
Why we are not allowed to use.

A(const A obj)

Answer 1

Copy Constructor is also a constructor whose main aim is to initialize the variable indirectly.
but here in copy constructor we are passing an object of the same class as a argument.
so, we can copy the value of that object into other one.

class sample
{
  int a;

  public:
    sample()
    {
        a = 10;
    }

    sample(&obj)
    {
        a = obj.a;
    }

    void show()
    {
        cout<<a;
    }
};

main()
{
  sample o1,o2;
  o1.show();
  o2.show();
}

in both it will print 10 on output screen;

Answer 2

Copy constructor is being used to create an object from an object of same class type. If a class has pointer variable as data member then copy constructor should be defined.
Default syntax to create an object as follows:

Class_Name(const Class_Name & obj)
{
// body of constructor
}