The George Washington University
School of Engineering and Applied Science
Department of Electrical Engineering and Computer Science
CSci 51 -- Spring 2002
Project #6
Due Date: start of class, March 26, 2002

This project depends upon Chapters 1-7, and provides experience with writing loops and robust input/output.

Write a package Date_Ops2. This package will have the following specification:

WITH Ada.Calendar;
PACKAGE Date_Ops2 IS
 
 TYPE Months IS (Jan, Feb, Mar, Apr, May, Jun,
 Jul, Aug, Sep, Oct, Nov, Dec);
 
 PROCEDURE Get (MonthName: OUT Months; 
  Day: OUT Ada.Calendar.Day_Number; 
 Year: OUT Ada.Calendar.Year_Number);
 -- Pre: None
 -- Post: The 3 values MonthName, Day, Year represent a valid date
 
END Date_Op2;

In the body of this package, the procedure Get will

• use the Robust_Input package to read the day and year robustly;
• use the ideas in Robust_Input (an exception loop) to read the month robustly;
• use Ada.Calendar.Time_Error to ensure that the date is valid.

A date like Feb. 30, or even Feb. 29 in a non-leap year, is invalid. As it happens, Ada.Calendar provides a built-in way to check the validity of a date. The function Ada.Calendar.Time_Of has the specification

 FUNCTION Time_Of (Year : Year_Number;
 Month : Month_Number;
 Day : Day_Number;
 Seconds : Day_Duration:=0.0) RETURN Time;

and returns a value of type Ada.Calendar.Time, if and only if the month/day/year combination forms a valid date. Otherwise, Time_Of raises the exception Ada.Calendar.Time_Error. Let's use this to check the validity of a date in the Get procedure: declare a variable in this procedure:

TestDate: Ada.Calendar.Time;

then call Ada.Calendar.Time_Of with the 3 parameters received by Get from the user.

Test.Date :=
 Ada.Calendar.Time_Of(Month => Month, Day => Day, Year => Year);

(Of course you need to convert MonthName to a month number, but you know how to do that!)

Now, put an exception loop in the body of Get whose handler looks like

EXCEPTION
 WHEN Ada.Calendar.Time_Error =>
 -- write message to user