12. protected class members

• 
  class Account {
  public:
      Account();
      bool sell( string symbol, int shares );
      bool buy( string symbol, int shares );
      bool deposit( double amount );
      bool withdraw( double amount );
  
  protected:
      void set_cash_balance( double amount );
  
  private:
      double m_cash_balance;
      static const int SIZE = 100;
      string m_holding_symbols[ SIZE ];
      int m_holding_shares[ SIZE ];
  
  };//class Account