Standalone program

 

Imagine a bank which maintains accounts of its customers. An object which implements such a bank account offers three operations: deposit a certain amount of money, withdraw a certain amount of money, and an operation called balance that returns the current account balance. The state of an account object consists of the current balance. The following C++ code fragment shows the class declaration for such an account object:

  class Account {
      long _current_balance;
  public:
      Account ();
      void deposit (unsigned long amount);
      void withdraw (unsigned long amount);
      long balance ();
  };

The above class declaration describes the interface and the state of an account object, the actual implementation which reflects the behavior of an account, is shown below:

  Account::Account ()
  {
      _current_balance = 0;
  }
  void Account::deposit (unsigned long amount)
  {
      _current_balance += amount;
  }
  void Account::withdraw (unsigned long amount)
  {
      _current_balance -= amount;
  }
  long Account::balance ()
  {
      return _current_balance;
  }

Here is a piece of code that makes use of a bank account:

  #include <iostream.h>

  int main (int argc, char *argv[])
  {
      Account acc;

      acc.deposit (700);
      acc.withdraw (250);
      cout << "balance is " << acc.balance() << endl;

      return 0;
  }

Since a new account has the initial balance of 0, the above code will print out ``balance is 450''.