IsLeapYear (was: Konvalina/Wileman exercises)

"Richard Heathfield" <rjh@[EMAIL PROTECTED]
> wrote in message 
news:4NmdnVQw8NGTJLHbnZ2dnUVZ8vmdnZ2d@[EMAIL PROTECTED]
>I recently picked up "Programming with Pascal", by Konvalina and
> Wileman, McGraw-Hill, 1987 (ISBN 0-07-100536-6). I have no idea whether
> this book is considered good by the Pascal community, but it seems
> reasonably well-written, at least.
>
> By chapter 3, the authors are ready to start setting exercises for which
> the solution is a complete Pascal program. There are eleven such
> exercises at the end of that chapter.
>
> I have coded solutions for these exercises, which include the problem
> specification in the introductory comment for each exercise.
>
> Since my home unaccountably lacks a resident Pascal expert, I would
> appreciate feedback on whether these are good answers.
>
> All eleven of them may be found here:
>
> http://www.cpax.org.uk/prg/****table/pascal/pwp/exercises/ch03/index.php
>
> (Could you please direct any responses to this newsgroup rather than to
> email, so that they can be peer-reviewed? Thanks.)
>

The isleapyear function in example 10 is implemented as:

  function isleapyear(year:integer):boolean;
  var leap:boolean;
  begin
    leap := false;
    if year mod 4 = 0 then
    begin
      leap := true;
      if year mod 100 = 0 then
      begin
        leap := false;
        if year mod 400 = 0 then
        begin
          leap := true;
        end
      end
    end;
    isleapyear := leap;
  end;

This could be alternatively implemented as follows:

function IsLeapYear(year: integer): boolean;
begin
   IsLeapYear := (year mod 4 = 0) and ((year mod 100 <> 0) or (year mod
400 
= 0))
end;

By way of explanation, consider this hypothetical Pascal example
(logically 
correct, but exaggerated to illustrate the point):

var
   a, b: boolean;
....
....
if (a <> true) then
   begin
      b := true
   end
else begin
  if a = true then
    begin
      b := false
    end
end;

This simplifies to:

  if a then b := false else b := true;

which further simplifies to:

  b := not a;

--
Chris Burrows
CFB Software
http://www.cfbsoftware.com/gpcp