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| 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 | 2015-10-26 11:22 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <87pp01lvr0.fsf@bsb.me.uk> (permalink) |
| References | <ba14ded1-d9f7-477e-a00f-cc47104c31f6@googlegroups.com> <aef31ddb-e264-43ac-a5db-64b881eca5bf@googlegroups.com> <75tp2bt23h0o4e81r8j4pvf0aqpafc5kis@4ax.com> <df0a7329-be47-4e24-80b0-35f6053400b3@googlegroups.com> <n0j8ha$du9$1@dont-email.me> |
Richard Heathfield <rjh@cpax.org.uk> writes:
<snip>
> You have already covered enough features of the language to enable you
> to write some quite powerful programs. There's still much to learn,
> but this might be a good time to take stock of what you have learned
> so far, and spend a couple of weeks just writing programs, rather than
> trying to learn new features.
>
> For example:
>
> Write a program that displays only the first n lines of its input.
Part of the trouble with so many books teaching programming is that they
insist in interactive input. The students write program that prompt for
input, the program reads is off it goes. That seems to be the case
here.
Your exercises (and they are otherwise very well chosen) don't work so
well in that context. For example, the "n" above has to come from the
same place as data whose lines are being read. And then the output
clutters up the screen as the user types more input. I think that in
order to set up and motivate this sort of exercise, the student needs to
know
(1) How to run programs (not write them) taking input from a file or a
pipe.[1]
(2) How to get simple data (like your n) from command-line arguments.
The first is easy though not always easy for a self-learning student.
The second is not hard, but will involve a degree of hand-waving about
arrays and pointers at the start but you can process simple command-line
arguments using standard boilerplate code anyway. The end result is
that the student can write tools that be combined in genuinely useful
ways. After writing
line-count -- count the number of input lines
head n -- output only the first n lines of input
match string -- output only lines that contain the given string
reverse -- reverse the order of the lines in the input
pick i j k... -- output only the numbered columns from each input line
sort -- sort the input by line
(all good exercises on their own) the student can then use these tools
to solve real problems.
> Write a program that displays only the /last/ n lines of its
> input. (Harder.)
I'd say that's a significant understatement unless you constrain the
problem with some fixed limits.
My preference was to use the "software tools" idea here too by asking
for a program to reverse the order of the input lines. The last 10
lines can then obtained by
<data reverse | head 10 | reverse
These exercises also build well one on another. For example, if you
implement reverse by reading the whole file (this is where you introduce
dynamic allocation), sort becomes a very simple extension to that.
> Write a program that displays only the leftmost n characters of each
> input line.
>
> Write a program that displays only the rightmost n characters of each
> input line. (Harder!)
>
> Write a program that displays only characters in columns x to y of
> each input line.
My preference here would be to concentrate on "columns" -- parts of a
line separated by one or more spaces. This lets the student build
slightly more useful programs.
<data | pick 2 1 | sort | pick 1 2
sorts by the second column an then puts the two columns back in order.
<snip other good exercises that are in a different vein>
[1] The most annoying thing in student programs -- including a hard-
wired input file name, or prompting for the name of the file to use!
--
Ben.
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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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