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Re: Program to compute elapsed time, learning structures and functions

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Alla _ <modelling.data@gmail.com> writes:
> Long time after I created this thread, I have corrected the 
> program, and it works now. Thank you for your help!
>
> // Program to computed elapsed time between two times
> #include <stdio.h>
>
> struct time
> {
>     int hour;
>     int minutes;
>     int seconds;
> };
>
> struct time elapsed_time (struct time time_1, struct time time_2);
[snip]

You're doing something to handle wraparound from one day to the next,
but I don't think you're doing it consistently.  This also interacts
oddly with out-of-order input.  For example:

 1:00:00  3:00:00 -->  02:00:00
 3:00:00  1:00:00 -->  22:00:00
49:00:00 00:00:00 --> -25:00:00
00:00:00 49:00:00 -->  49:00:00

You need a consistent definition of how the program should behave in
these corner cases -- which includes defining just what you mean by
"elapsed time".  Restricting the permitted input values (and aborting
with an error message when the restrictions are violated) is a
reasonable approach if you don't want to handle bizarre inputs.

You have a great deal of code in your elapsed_time function that
deals with the hour, minutes, and seconds fields separately.
An alternative approach (one that I'd probably use) is to convert
the "struct time" value to a raw number of seconds, compute the
difference, and then convert back to a "struct time" result.

Encapsulating the struct time <--> raw seconds conversions into their
own functions would IMHO make the code easier to read and understand.

There might be some concern for overflow, if
    3600*hour + 60*minute + seconds
might exceed INT_MAX, but storing raw seconds in a long or even
a long long would avoid that for any "reasonable" time intervals.
Storing a number of seconds in a "long" covers an interval of at
least 68 years.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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Program to compute elapsed time, learning structures and functions Alla _ <modelling.data@gmail.com> - 2015-10-09 02:36 -0700
  Re: Program to compute elapsed time, learning structures and functions Bartc <bc@freeuk.com> - 2015-10-09 10:48 +0100
    Re: Program to compute elapsed time, learning structures and functions Alla _ <modelling.data@gmail.com> - 2015-10-09 03:06 -0700
  Re: Program to compute elapsed time, learning structures and functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-09 11:01 +0100
    Re: Program to compute elapsed time, learning structures and functions Alla _ <modelling.data@gmail.com> - 2015-10-09 03:07 -0700
  Re: Program to compute elapsed time, learning structures and functions Richard Heathfield <rjh@cpax.org.uk> - 2015-10-09 13:26 +0100
    Re: Program to compute elapsed time, learning structures and functions Alla _ <modelling.data@gmail.com> - 2015-10-09 06:49 -0700
      Re: Program to compute elapsed time, learning structures and functions Bartc <bc@freeuk.com> - 2015-10-09 16:20 +0100
        Re: Program to compute elapsed time, learning structures and functions Alla _ <modelling.data@gmail.com> - 2015-10-09 09:27 -0700
        Re: Program to compute elapsed time, learning structures and functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-09 19:29 +0100
        Re: Program to compute elapsed time, learning structures and functions Keith Thompson <kst-u@mib.org> - 2015-10-09 14:06 -0700
          Re: Program to compute elapsed time, learning structures and functions Bartc <bc@freeuk.com> - 2015-10-09 22:24 +0100
            Re: Program to compute elapsed time, learning structures and functions Keith Thompson <kst-u@mib.org> - 2015-10-09 15:51 -0700
      Re: Program to compute elapsed time, learning structures and functions Richard Heathfield <rjh@cpax.org.uk> - 2015-10-09 18:26 +0100
        Re: Program to compute elapsed time, learning structures and functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-09 19:24 +0100
          Re: Program to compute elapsed time, learning structures and functions Richard Heathfield <rjh@cpax.org.uk> - 2015-10-09 19:50 +0100
            Re: Program to compute elapsed time, learning structures and functions Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-10-09 15:56 -0400
      Re: Program to compute elapsed time, learning structures and functions James Kuyper <jameskuyper@verizon.net> - 2015-10-09 15:31 -0400
      Re: Program to compute elapsed time, learning structures and functions Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-10 06:57 -0700
        Re: Program to compute elapsed time, learning structures and functions Bartc <bc@freeuk.com> - 2015-10-10 17:25 +0100
          Re: Program to compute elapsed time, learning structures and functions Bartc <bc@freeuk.com> - 2015-10-10 19:12 +0100
          Re: Program to compute elapsed time, learning structures and functions Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-10 20:56 +0100
            Re: Program to compute elapsed time, learning structures and functions Bartc <bc@freeuk.com> - 2015-10-10 21:52 +0100
          Re: Program to compute elapsed time, learning structures and functions Keith Thompson <kst-u@mib.org> - 2015-10-10 17:57 -0700
            Re: Program to compute elapsed time, learning structures and functions raltbos@xs4all.nl (Richard Bos) - 2015-10-11 10:09 +0000
            Re: Program to compute elapsed time, learning structures and functions Bartc <bc@freeuk.com> - 2015-10-11 11:26 +0100
              Re: Program to compute elapsed time, learning structures and functions Keith Thompson <kst-u@mib.org> - 2015-10-11 14:12 -0700
            Re: Program to compute elapsed time, learning structures and functions Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-15 10:51 -0700
              Re: Program to compute elapsed time, learning structures and functions Keith Thompson <kst-u@mib.org> - 2015-10-15 11:25 -0700
                Re: Program to compute elapsed time, learning structures and functions Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-16 05:34 -0700
                Re: Program to compute elapsed time, learning structures and functions Keith Thompson <kst-u@mib.org> - 2015-10-16 08:52 -0700
          Re: Program to compute elapsed time, learning structures and functions Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-15 10:46 -0700
            Re: Program to compute elapsed time, learning structures and functions Bartc <bc@freeuk.com> - 2015-10-15 19:06 +0100
              Re: Program to compute elapsed time, learning structures and functions Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-16 05:24 -0700
          Re: Program to compute elapsed time, learning structures and functions glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-17 00:10 +0000
      Re: Program to compute elapsed time, learning structures and functions Barry Schwarz <schwarzb@dqel.com> - 2015-10-18 09:52 -0700
  Re: Program to compute elapsed time, learning structures and functions Alla _ <modelling.data@gmail.com> - 2015-10-09 06:52 -0700
    Re: Program to compute elapsed time, learning structures and functions Barry Schwarz <schwarzb@dqel.com> - 2015-10-18 10:21 -0700
      Re: Program to compute elapsed time, learning structures and functions Alla _ <modelling.data@gmail.com> - 2015-11-05 00:56 -0800
        Re: Program to compute elapsed time, learning structures and functions Barry Schwarz <schwarzb@dqel.com> - 2015-11-05 01:55 -0800
          Re: Program to compute elapsed time, learning structures and functions Alla _ <modelling.data@gmail.com> - 2015-11-05 02:55 -0800
          Re: Program to compute elapsed time, learning structures and functions Alla _ <modelling.data@gmail.com> - 2015-11-05 03:01 -0800
            Re: Program to compute elapsed time, learning structures and functions Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-05 03:41 -0800
              Re: Program to compute elapsed time, learning structures and functions Alla _ <modelling.data@gmail.com> - 2015-11-05 06:55 -0800
          Re: Program to compute elapsed time, learning structures and functions Alla _ <modelling.data@gmail.com> - 2015-11-05 03:03 -0800
            Re: Program to compute elapsed time, learning structures and functions Richard Heathfield <rjh@cpax.org.uk> - 2015-11-05 13:27 +0000
              Re: Program to compute elapsed time, learning structures and functions Alla _ <modelling.data@gmail.com> - 2015-11-05 06:54 -0800
        Re: Program to compute elapsed time, learning structures and functions Keith Thompson <kst-u@mib.org> - 2015-11-05 12:42 -0800
          Re: Program to compute elapsed time, learning structures and functions Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-05 15:50 -0800

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