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From: "Nasser M. Abbasi" <nma@12000.org>
Newsgroups: comp.lang.ada
Subject: Re: How do I write directly to a memory address?
Date: Tue, 08 Feb 2011 01:01:59 -0800
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Date: 2011-02-08T01:01:59-08:00
List-Id: <comp.lang.ada>

On 2/8/2011 12:04 AM, Ludovic Brenta wrote:
> Georg Bauhaus wrote:
>>> Well, I came to wonder what intentions are conveyed by "void foo (int
>>> arg)" and why modifying arg inside foo could be intentional.  Since I
>>> came up with no convincing reason (the only reasons being variants of
>>> premature optimization), I concluded that the possibility of "void foo
>>> (int arg)" as opposed to "void foo (const int arg)" was a flaw in the
>>> C language, that cost me a lot of effort.
>>
>> Ease of implementation when pushing parameters?
>>
>> void foo(int countdown)
>> {
>>    while (--countdown) {
>>      fputc('.', stdout);
>>    }
>>    fputc('\n', stdout);
>> }
>
>

>
> BTW, like I said, *every* time I look at C code,

This is funny, but I understand what you mean.

> I see a bug. In your
> case, foo has undefined behavior if countdown is negative.
>

If I remember my C, since "while" will keep running until its argument
becomes false, which in C means "zero", then this means if countdown is
negative the above code will keep decrementing countdown until it hits
-infinity? :) and the program will crash or do something else?
  
> Also, note how the Ada version of this function does not use a
> variable at all; it uses a for loop inside of which K is constant. And
> it does not have your bug:
>
> procedure Foo (Countdown : in Natural) is
> begin
>     for K in 1 .. Countdown loop
>        Put ('.');
>     end loop;
>     Next_Line;
> end Foo;
>
> So, "ease of implementation" is not a good reason.  The thing you
> implemented "easily" had a bug.
>
> --
> Ludovic Brenta.

Ada has so many nice things in it. I think its type system is one
of the best features of Ada.

--Nasser