2.1   Specification

        Execute the following sequence of actions on a bank account:
 

1.    Read in and show the balance of a bank account.

2.    Deposit an amount, withdraw an amount, and show the balance. Read in the amounts         from the user.

3.    Add interest for one day, using an annual interest rate of 4.5%. Show the balance.

2.2   Analysis

        There is one class in this system, class ACCOUNT. The data in an account are the balance and the interest rate. The system goals are to read in and store the balance, deposit money, withdraw money, and show the balance.
 
 

2.3   Solution design

        The creation routine make contains all the code. This is not a good OO solution, but it is the only thing we can do until routines are covered in the next chapter. The client chart is unchanged from the previous part of the case study.

        A new variable named amount is used to hold the amounts to deposit and withdraw. The amount is read from the user, used to change the balance, and that value is not used again. The amount to deposit (withdraw) is not part of the state of the object; the state of the object is defined by its balance and rate. The variable amount should be local, but it has to be defined as a class attribute until routines are covered in the next chapter.
 
 

2.4   Solution code

        The listing for class ACCOUNT is given below. This is the root class for the system, with one routine named make that contains all the executable code, so the Ace file is unchanged.
 

class ACCOUNT

creation
        make

feature
        balance: REAL
        rate: REAL is 4.5
        amount: REAL

        make is
                       -- use the account
             do
                        io.new_line
                       io.putstring ("%TInitial account balance: $")
                        io.readreal
                        balance := io.lastreal
                        io.putstring ("%NThe balance is $")
                        io.putreal (balance)

                        io.putstring ("%Tamount to deposit: $")
                        io.readreal
                        amount := io.lastreal
                        balance := balance + amount

                        io.putstring ("%Tamount to withdraw: $")
                        io.readreal
                        amount := io.lastreal
                        balance := balance - amount

                        io.new_line
                        io.putstring ("%NThe balance is $")
                        io.putreal (balance)

                        balance := balance + balance * (rate / 100.0) / 365.25 -- add interest today

                        io.new_line
                        io.new_line
                        io.putstring ("%NThe balance is $")
                        io.putreal (balance)
                        io.new_line
                end -- make

end -- class ACCOUNT