text: // Fig. 10.3: PhoneNumber.h
  // PhoneNumber class definition
  
  #ifndef PHONENUMBER_H
  #define PHONENUMBER_H
  
  #include <iostream>
  #include <string>
  
  class PhoneNumber {
  
      friend std::ostream& operator<<(std::ostream&, const PhoneNumber&);
      friend std::istream& operator>>(std::istream&, PhoneNumber&);
  
      private:
  
          std::string areaCode; // 3-digit
          std::string exchange; // 3-digit exchange
          std::string line;     // 4-digit lines
  
  };
  
  #endif