Object-oriented Software in Ada 95

A Text user interface 315
with Class_Window;
use Class_Window;
package Pack_Program is
procedure Main;
private
P_Result : P_Window;
end Pack_Program;
The call-back function User_Input is executed when a user has entering the distance in miles and then
pressed Enter. This entered distance is converted to a floating point number using the procedure get in
Ada.Float_Text_Io to convert a string into an instance of a Float. If the number is not valid or an error in
the calculation occurs, then an appropriate message is displayed to the user.
with Ada.Text_Io, Ada.Float_Text_Io;
use Ada.Text_Io, Ada.Float_Text_Io;
with Class_Input_Manager, Class_Window, Class_Dialog;
use Class_Input_Manager, Class_Window, Class_Dialog;
package body Pack_Program is
function User_Input( Cb_Mes:in String ) return String is
Miles : Float; --Miles input by user
Last : Positive; --
Str_Kms: String( 1 .. 10 ); --As a string in Kms
Str_Mls: String( 1 .. 10 ); --As a string in Miles
Begin
begin
Get( Cb_Mes & ".", Miles, Last );
Put( Str_Kms, Miles * 1.609_344, Aft=>2, Exp=>0 );
Put( Str_Mls, Miles, Aft=>2, Exp=>0 );
Put( P_Result.all, "Distance in Miles = " );
Put( P_Result.all, Str_Mls ); New_Line( P_Result.all );
Put( P_Result.all, "Distance in Kms = " );
Put( P_Result.all, Str_Kms ); New_Line( P_Result.all );
exception
when Data_Error =>
Put( P_Result.all, " Not a valid number" );
New_Line( P_Result.all );
when others =>
Put( P_Result.all, " [Calculation error]" );
New_Line( P_Result.all );
end;
return "";
end User_Input;
Note:
The call-back function returns a string as its result. This provides a mechanism for returning
information to the environment which called it. In this particular case, no information is returned.
.A decimal point (.0) is appended to the user's input to allow a user to enter an integer value and still
have the number processed correctly.
The package Ada.Text_Io is required for the exception Data_Error.
In the procedure Main the three windows that will be displayed are declared. Then the call-back function
User_Input is associated with dialog window and the program executes and waits for a user interaction.
© M A Smith - May not be reproduced without permission