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Groups > comp.lang.c > #150521
| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: How to div only once to get remainder and quotient? |
| Date | 2020-03-12 21:11 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <87o8t1s2gt.fsf@bsb.me.uk> (permalink) |
| References | <r4e5ff$t02$1@dont-email.me> |
Francis Assissi <invalid@invalid.invalid> writes:
> The following code serves to convert a decimal number to binary,
The number is already in binary when you start work on it. What your
code does is convert a binary number to a string of 0 and 1 characters.
This is not just word play. Since the number is stored as a collection
of bits, you can convert to 0/1 character without doing and divisions at
all.
> but this conversion requires dividing twice: once to get quotient,
> another to get the remainder. Is there a function to get both in a
> single operation like it is possible with Assembly?
Yes: div declared in stdlib.h.
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
>
> #define LENGTH 32
Keeping your fingers crossed that that is enough! One day you will
enhance the code to deal with, say, negative numbers and you might
forget to change this. You can use sizeof and CHAR_BIT to calculate a
size that is big enough.
> int main(void)
> {
> int number = 1234567890;
> char bin_string[LENGTH] = {0};
There's no need to set the array to all zeros. You set is all
immediately below.
> char *ptr = bin_string + LENGTH - 1;
>
> memset(bin_string, '0', LENGTH);
You can use sizeof bin_string if you want to avoid repeating LENGTH.
> *ptr = '\0';
> --ptr;
> while(number > 0 && ptr > bin_string) {
This condition is wrong. It prevents the very first position in
bin_string from being used, and you need all 32 positions just for
positive integers (31 zero/one bits and a nul at the end).
> *ptr = '0' + number % 2;
> number /= 2;
If you want to avoid division, use bit operations: number & 1 gives you
the bottom bit, and number >>= 1 shifts the bits to the right. I can
safely suggest this because your code only deals with positive numbers.
To handle negative numbers you need to take more care.
But it is very likely that the compiler will replace you % and /
operators anyway. These days, it is almost always better to write what
you mean as clearly as possible and let the compiler do its thing.
> --ptr;
> }
Here you have an interesting condition you could test for. One thing I
always do after a while loop is to ask "what do I know here?". One
thing I know here is that either number == 0 or ptr <= bin_string. If I
get here with number != 0 I know the buffer ran out of space. Since you
put both tests in while condition, you presumably though that either of
them might stop the loop. If so, you should probably take some action
here if number is not zero.
> puts(bin_string);
> exit(EXIT_SUCCESS);
> }
--
Ben.
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How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-12 20:18 +0000
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-12 20:26 +0000
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-12 20:30 +0000
Re: How to div only once to get remainder and quotient? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-03-12 20:40 -0700
Re: How to div only once to get remainder and quotient? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-03-12 16:38 -0400
Re: How to div only once to get remainder and quotient? richard@cogsci.ed.ac.uk (Richard Tobin) - 2020-03-12 20:44 +0000
Re: How to div only once to get remainder and quotient? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-03-12 17:00 -0400
Re: How to div only once to get remainder and quotient? richard@cogsci.ed.ac.uk (Richard Tobin) - 2020-03-13 09:35 +0000
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-13 11:12 +0100
Re: How to div only once to get remainder and quotient? scott@slp53.sl.home (Scott Lurndal) - 2020-03-12 22:16 +0000
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-12 22:39 +0000
Re: How to div only once to get remainder and quotient? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-03-12 19:51 -0400
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-13 00:47 +0000
Re: How to div only once to get remainder and quotient? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-03-12 23:02 -0400
Re: How to div only once to get remainder and quotient? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-03-12 20:39 -0700
Re: How to div only once to get remainder and quotient? scott@slp53.sl.home (Scott Lurndal) - 2020-03-13 15:00 +0000
Re: How to div only once to get remainder and quotient? Spiros Bousbouras <spibou@gmail.com> - 2020-03-14 08:35 +0000
Re: How to div only once to get remainder and quotient? jak <nospam@please.ty> - 2020-03-12 21:55 +0100
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-12 21:56 +0000
Re: How to div only once to get remainder and quotient? jak <nospam@please.ty> - 2020-03-12 23:26 +0100
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-12 21:11 +0000
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-12 21:57 +0000
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-12 22:23 +0000
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-13 01:05 +0000
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-13 11:33 +0100
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-13 11:03 +0000
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-13 14:31 +0100
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-13 15:12 +0000
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-13 18:03 +0100
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-13 18:01 +0000
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-13 19:06 +0100
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-13 19:12 +0000
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-13 13:34 +0000
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-13 15:00 +0000
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-13 20:34 +0000
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-13 21:41 +0000
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-14 01:47 +0000
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-14 12:24 +0000
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-14 16:35 +0000
Re: How to div only once to get remainder and quotient? Bart <bc@freeuk.com> - 2020-03-14 18:05 +0000
Re: How to div only once to get remainder and quotient? already5chosen@yahoo.com - 2020-03-13 03:52 -0700
Re: How to div only once to get remainder and quotient? Guillaume <message@bottle.org> - 2020-03-13 16:41 +0100
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-13 16:07 +0000
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-13 18:10 +0100
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-13 19:32 +0000
Re: How to div only once to get remainder and quotient? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-03-13 16:08 -0400
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-13 20:50 +0000
Re: How to div only once to get remainder and quotient? jameskuyper@stellarscience.com - 2020-03-13 16:05 -0700
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-13 23:42 +0000
Re: How to div only once to get remainder and quotient? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-03-13 19:59 -0400
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-14 00:07 +0000
Re: How to div only once to get remainder and quotient? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-03-13 20:27 -0400
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-14 01:37 +0000
Re: How to div only once to get remainder and quotient? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-04-02 07:45 -0700
Re: How to div only once to get remainder and quotient? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-04-02 08:09 -0700
Re: How to div only once to get remainder and quotient? gazelle@shell.xmission.com (Kenny McCormack) - 2020-04-02 16:03 +0000
Re: How to div only once to get remainder and quotient? Öö Tiib <ootiib@hot.ee> - 2020-04-04 04:31 -0700
Invitations (Was: How to div only once to get remainder and quotient?) gazelle@shell.xmission.com (Kenny McCormack) - 2020-04-04 17:04 +0000
Re: Invitations (Was: How to div only once to get remainder and quotient?) Öö Tiib <ootiib@hot.ee> - 2020-04-07 00:10 -0700
Re: How to div only once to get remainder and quotient? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-03-13 14:30 -0400
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-13 20:54 +0000
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-13 23:10 +0000
Re: How to div only once to get remainder and quotient? James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-03-13 20:18 -0400
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-14 00:34 +0000
Re: How to div only once to get remainder and quotient? Francis Assissi <invalid@invalid.invalid> - 2020-03-14 01:47 +0000
Re: How to div only once to get remainder and quotient? Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-03-13 14:39 -0600
Re: How to div only once to get remainder and quotient? felix@palmen-it.de (Felix Palmen) - 2020-03-13 22:10 +0100
Re: How to div only once to get remainder and quotient? Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-03-13 16:26 -0600
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-14 16:41 +0100
Re: How to div only once to get remainder and quotient? felix@palmen-it.de (Felix Palmen) - 2020-03-14 17:00 +0100
Re: How to div only once to get remainder and quotient? David Brown <david.brown@hesbynett.no> - 2020-03-15 13:39 +0100
Re: How to div only once to get remainder and quotient? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-13 23:07 +0000
Re: How to div only once to get remainder and quotient? Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-03-14 12:13 -0600
Re: How to div only once to get remainder and quotient? Bonita Montero <Bonita.Montero@gmail.com> - 2020-04-07 09:35 +0200
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