Question need help to complete below:

Consider the following incomplete class definitions. Fill in the missing code as described in the comments. Your solution should call the appropriate set and get functions on a Book object.

class Book{

public:

//Provide:

// - a pure virtual function to set the ISBN/eISBN

// - a pure virtual function to get the ISBN/eISBN

};

// create an EBook class that inherits from Book

{

int eISBN;

public:

void set(const int _eISBN){eISBN=_eISBN;};

int get() const{return eISBN;};

};

// create a PaperBook class that inherits from Book

{

int isbn;

public:

void set(const int _isbn){isbn=_isbn};

int get() const{return isbn;};

};

Additionally, describe in a couple of sentences the purpose of a pure virtual member function.