Re: Issues with setting variables to true or false: how does the compiler understands it

From	Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups	comp.lang.c
Subject	Re: Issues with setting variables to true or false: how does the compiler understands it
Date	2015-10-27 19:47 +0000
Organization	A noiseless patient Spider
Message-ID	<87h9lchz52.fsf@bsb.me.uk> (permalink)
References	(5 earlier) <n0mdfd$bbe$1@dont-email.me> <slrnn2urkt.5q5.grahn+nntp@frailea.sa.invalid> <n0nrhi$cdk$1@dont-email.me> <87y4eoigva.fsf@bsb.me.uk> <n0nuqi$oo3$1@dont-email.me>

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Richard Heathfield <rjh@cpax.org.uk> writes:

> On 27/10/15 13:24, Ben Bacarisse wrote:
>> Richard Heathfield <rjh@cpax.org.uk> writes:
<snip>
>>> I'd go further than that, and say that it was okay for the programmer
>>> to *assume* that lines would be no longer than a certain length, and
>>> that n (the number of lines to print) would be no higher than a
>>> certain number...
>>
>> I think that's a little odd.  That might be the Pascal way (I don't
>> recall) but it seems an odd design to force on someone learning C.  Line
>> oriented input is a pain in C and using it adds another failure mode to
>> the program.
>
> I wasn't planning on forcing that design on anyone. I'm just leaving
> it open. Not quite the same thing.

Maybe the force is the wrong word, but if you specify that limited line
length and limited n are permitted, you probably won't get many designs
other than the one you already have in your mind.

>> I'd suggest the student limit only the number of bytes to buffer since
>> the purpose of a limit is simply to avoid teaching about growing buffers
>> too soon.  There's no obvious advantage (unless I'm missing it) to
>> limiting both line length and the maximum number of lines.
>
> Well, it means you can do this:
>
> #define MAX_LINE_LENGTH 60
> #define MAX_HISTORY 10
>
> char history[MAX_HISTORY][MAX_LINE_LENGTH] = {0};
>
> and then the implementation is pretty much obvious from that point on.

Yes, I was not in doubt about that part!  I should probably not comment
further until I've written it both ways, but having only one limitation
looks better to me than having two.  Maybe maintaining a circular buffer
of characters is messier than I'm imagining.  I'll see if I have time
(and inclination) later.

>> <snip>
>>>> but if I used a tail
>>>> utility and it didn't cope with thousands of characters, I'd be
>>>> disappointed: that wouldn't be "reasonable" in that context.
>>>
>>> Yep. The key point is that a fundamental distinction must be made
>>> between throwaway academic exercises and robust software tools.
>>
>> I'm worried by that idea, as least in the way it's phrases.  I think the
>> distinction should be *minimised* wherever possible.
>
> I think that "wherever possible" should not include the very early
> stages of learning to write programs. When a kid builds his or her
> first pramwheels-and-string go-kart, it is unkind to insist that it is
> fitted with air-bags. (Proof by analogy is fraud, of course. This is
> illustration by analogy, quite a different thing.)

It's possible we agree -- I'm not really sure.  We may both simply be
putting it in terms the other can't quite accept.  I say that because:

>> That involves
>> carefully choosing exercises so that it is not necessary to make too
>> many unrealistic simplifications, and to teach, wherever possible, "best
>> practise".  That's hard to define, of course, but I mean, very roughly,
>> best practice given the fewest simplify assumptions about the program's
>> overall design.
>
> Taking that paragraph purely on its own merits without the surrounding
> context, I think I'd agree. In fact, I think the key phrase is
> "carefully choosing exercises". Looking back on my suggested list, I
> recognise that I wasn't as careful as I should have been!

To take the go-kart analogy further, the exercise is not to build a
child-safe racing vehicle -- it's to build something fun to ride, often
with only what you find lying around.  Airbags will never be part of
that.

The hard part is to come up with exercises that are fun, don't use
anything the student does not have "lying round", but that can be done
well without too many compromises.  It's only that last part that's in
dispute because your phrase about a fundamental distinction with
throwaway academic exercises suggests a difference about what
constitutes too many compromises.

>> We are probably not too far apart on this point but the way you phrase
>> it suggests you might be happy with what, for me, would be unacceptable
>> designs, because you've put a huge wall between throwaway academic
>> exercises and properly usable tools.  I believe one should try to make
>> as little distinction between these as is practical.
>
> I think there /is/ a huge wall between early learning and best
> practice.

Take a classic that drives me mad every time I see it: write a program
to convert degrees C to degrees F.  The intended solution is usually a
tedious thing that uses interactive input and does a simple calculation.
I'd prefer to teach the use of command-line arguments and a simple call
to atof or strtod because that's the sort of conversion tool I might
actually use (and it extends well for later more challenging exercises).

Now it's true that there is some noise in using argv, but it does not
need very much more in terms of explanation (and hand waving) than scanf
or fgets, and the result is, trivial though it may be, closer to "best
practice" than the usual "simple" solution.  I say "closer" because I'd
probably leave returning a useful status for later programs.  Best
practise would require one to be returned, of course, so this is simply
closer to best practice than the usual solution.

<snip>
-- 
Ben.

Thread

Issues with setting variables to true or false: how does the compiler understands it Alla _ <modelling.data@gmail.com> - 2015-10-24 02:17 -0700
  Issues with setting variables to true or false: how does the compiler understands it asetofsymbols@gmail.com - 2015-10-24 03:29 -0700
    Re: Issues with setting variables to true or false: how does the compiler understands it Alla _ <modelling.data@gmail.com> - 2015-10-24 03:38 -0700
  Re: Issues with setting variables to true or false: how does the compiler understands it Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-24 04:30 -0700
    Re: Issues with setting variables to true or false: how does the compiler understands it gazelle@shell.xmission.com (Kenny McCormack) - 2015-10-24 12:04 +0000
  Issues with setting variables to true or false: how does the compiler understands it asetofsymbols@gmail.com - 2015-10-24 04:59 -0700
    Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-24 14:28 +0100
      Re: Issues with setting variables to true or false: how does the compiler understands it asetofsymbols@gmail.com - 2015-10-24 07:26 -0700
        Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-24 17:06 +0100
  Re: Issues with setting variables to true or false: how does the compiler understands it James Kuyper <jameskuyper@verizon.net> - 2015-10-24 11:56 -0400
    Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-24 12:02 -0700
      Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-24 15:45 -0700
        Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-24 16:28 -0700
          Re: Issues with setting variables to true or false: how does the compiler understands it Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-24 16:44 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-24 19:34 -0700
          Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-24 19:30 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-24 20:33 -0700
          Re: Issues with setting variables to true or false: how does the compiler understands it Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-28 11:16 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-10-28 15:12 -0400
              Re: Issues with setting variables to true or false: how does the compiler understands it Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-29 12:18 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it raltbos@xs4all.nl (Richard Bos) - 2015-10-29 21:51 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-30 08:38 -0700
              Re: Issues with setting variables to true or false: how does the compiler understands it Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-30 05:34 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-28 14:08 -0700
              Re: Issues with setting variables to true or false: how does the compiler understands it Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-30 06:14 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-28 21:50 +0000
              Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-28 15:08 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-28 22:47 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Robert Wessel <robertwessel2@yahoo.com> - 2015-10-28 18:35 -0500
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-28 18:12 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-29 01:35 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Robert Wessel <robertwessel2@yahoo.com> - 2015-10-28 21:12 -0500
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-28 19:52 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-28 18:01 -0700
              Re: Issues with setting variables to true or false: how does the compiler understands it Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-30 03:47 -0700
  Re: Issues with setting variables to true or false: how does the compiler understands it Barry Schwarz <schwarzb@dqel.com> - 2015-10-24 09:54 -0700
  Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-24 12:13 -0700
  Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-24 21:50 +0100
  Re: Issues with setting variables to true or false: how does the compiler understands it Alla _ <modelling.data@gmail.com> - 2015-10-25 04:04 -0700
    Re: Issues with setting variables to true or false: how does the compiler understands it Barry Schwarz <schwarzb@dqel.com> - 2015-10-25 08:32 -0700
      Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-25 18:19 +0000
      Re: Issues with setting variables to true or false: how does the compiler understands it Alla _ <modelling.data@gmail.com> - 2015-10-25 11:30 -0700
        Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-25 18:56 +0000
          Re: Issues with setting variables to true or false: how does the compiler understands it Alla _ <modelling.data@gmail.com> - 2015-10-25 20:59 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it Anand Hariharan <mailto.anand.hariharan@gmail.com> - 2015-10-25 21:49 -0700
              Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-26 08:10 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Anand Hariharan <mailto.anand.hariharan@gmail.com> - 2015-10-26 16:05 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-27 00:34 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-27 09:04 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-27 21:24 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-26 18:16 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-27 02:33 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-27 09:08 -0700
          Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-26 11:22 +0000
            Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-26 11:35 +0000
              Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-26 17:00 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-26 17:59 +0000
          Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-26 07:55 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-26 17:06 +0000
            Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-26 10:56 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-26 20:14 +0000
              Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-26 17:09 -0700
          Re: Issues with setting variables to true or false: how does the compiler understands it Bartc <bc@freeuk.com> - 2015-10-26 23:39 +0000
            Re: Issues with setting variables to true or false: how does the compiler understands it Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-27 12:31 +0000
              Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-27 12:45 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-27 13:24 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-27 13:41 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-27 19:43 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-27 19:47 +0000
              Re: Issues with setting variables to true or false: how does the compiler understands it Bartc <bc@freeuk.com> - 2015-10-27 13:20 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-27 13:28 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-27 13:54 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-27 07:51 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Bartc <bc@freeuk.com> - 2015-10-27 16:46 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-27 10:52 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Bartc <bc@freeuk.com> - 2015-10-27 18:51 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-27 12:17 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Bartc <bc@freeuk.com> - 2015-10-27 19:34 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-27 13:10 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-27 13:41 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Bartc <bc@freeuk.com> - 2015-10-27 23:11 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-27 19:02 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it gazelle@shell.xmission.com (Kenny McCormack) - 2015-10-28 07:09 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-28 11:27 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-27 12:27 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-27 13:18 -0700

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