text: #pragma once
  class Account {
   public:
      Account();
  
      Account(int id, int balance);
    virtual ~Account();
  
    // Virtual to test.
    virtual int GetBalance() const;
  
    // Virtual to test.
    virtual void ChangeBalance(int diff);
  
    // Virtual to test.
    virtual void Lock();
  
    // Virtual to test.
    virtual void Unlock();
    int id() const { return id_; }
  
   private:
    int id_;
    int balance_;
    bool is_locked_;
  };
  