#ifndef _Number_h_
#define _Number_h_

/* Abstract base class 'Number' (no objects can be created) */

class Number
{
  public:
  
    Number();            // default constructor
    Number(const Number &other); // copy constructor

    virtual ~Number();   // destructor
       
    virtual void read() = 0;          // read value from 'cin' (abstract method) 
    virtual void write() const = 0;   // write value to 'cout' (abstract method; object is not changed)

    static int noOfNumbers();   // return number of instances (static member function)

  private:

    static int count;   // number of instances (static var: only one instance for the whole class)
};

#endif