14. Constructing a derived class example

• 
  // Base
  class Account {
  public:
      Account( int bal );
  };// class Account
  
  
  // Derived
  class GoldAccount : public Account {
  public:
      GoldAccount( int bal );
  private:
      int m_margin_balance;
  };// class GoldAccount
  
  
  // Derived constructor invokes base constructor:
  GoldAccount::GoldAccount( int bal )
  : Account( bal ),
    m_margin_balance( 0 )
  {
  }