Object-oriented Software in Ada 95

The main body of the program processes the option selected by the user.
Packages as classes 89
begin
loop
Menu( Screen, "Deposit", "Withdraw", "Balance", "" );
case Event( Screen ) is
when M_1 =>
--Deposit
Dialog( Screen, "Amount to deposit", Cash );
if Cash
--Withdraw
Dialog( Screen, "Amount to withdraw", Cash );
if Cash
--Exit
return;
when others =>
--Not used
end case;
end loop;
end Main;
6.12 Class TUI
Message( Screen, "Program error");
The full specification for the class TUI is:
--oops
package Class_TUI is
type Menu_Item is ( M_1, M_2, M_3, M_4, M_Quit );
type TUI is private;
procedure Menu( The:in out TUI; M1,M2,M3,M4:in String );
function Event( The:in TUI ) return Menu_Item;
procedure Message( The:in TUI; Mes:in String );
procedure Dialog(The:in TUI; Mes:in String; Res:out Float);
procedure Dialog(The:in TUI; Mes:in String; Res:out Integer);
private
type TUI is record
Selection : Menu_Item := M_Quit;
end record;
end Class_TUI;
In the implementation of the class TUI the most complex method is menu. This method is implemented as a
procedure that writes out the menu for the TUI and reads the user’s response. It will only complete when a valid
response has been received from the user. In the implementation of the procedure the technique of procedural
decomposition is used to simplify the code.
In procedural decomposition, a large body of code is split into several procedures or functions. This helps to
reduce complexity making construction and maintenance easier.
© M A Smith - May not be reproduced without permission