Fixed number of digits printing of integers (ex: 0001 to 0100)

Discussion in 'C Programming' started by Michel Rouzic, Dec 9, 2005.

  1. I can't think of a simple way to print integers with a fix number of
    digits, in order to obtain something like 0001 for 1 and 0100 for 100
    automatically just by specifying in a variable the number of desired
    digits.

    I thought about printing to a variable using for example %4d and then
    replace ' ' by '0', but I don't know if i can print to an array, and
    then I don't think I can put a variable between % and d to specify the
    number of digits I want.

    I thought that maybe there would be some already existing and easy way
    to do it that I don't know of, otherwise i'd like to know how people
    usually deal with that problem, thanks
     
    Michel Rouzic, Dec 9, 2005
    #1
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  2. Michel Rouzic

    jacob navia Guest

    Michel Rouzic a écrit :
    #include <stdio.h>
    int main(void)
    {
    for (int i=4; i<10;i++)
    printf("%05d\n",i*100);
    int width=6;
    printf("%0*d\n",width,746);
    }

    Output
    00400
    00500
    00600
    00700
    00800
    00900
    000746
     
    jacob navia, Dec 9, 2005
    #2
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  3. Michel Rouzic

    Mike Wahler Guest

    #include <stdio.h>

    int main()
    {
    int i = 0;

    for(i = 1; i < 101; ++i)
    printf("%04d\n", i);

    return 0;
    }

    Where's your textbook?

    -Mike
     
    Mike Wahler, Dec 9, 2005
    #3
  4. Try "%04d"

    -David
     
    David Resnick, Dec 9, 2005
    #4
  5. Michel Rouzic

    Ben Pfaff Guest

    int num_digits = 4;
    int value = ...whatever...;
    printf("%0*d\n", num_digits, value);

    You should really get a C reference manual.
     
    Ben Pfaff, Dec 9, 2005
    #5
  6. sprintf("%04d", some_int);
     
    Kleuskes & Moos, Dec 9, 2005
    #6
  7. Thanks. Got no textbook. n869.pdf is all I got. Plus i'm learning C on
    my own
     
    Michel Rouzic, Dec 9, 2005
    #7
  8. OK thanks. All i got is n869.pdf, otherwise I have nothing else. What
    else should I get?
     
    Michel Rouzic, Dec 9, 2005
    #8
  9. Michel Rouzic

    Ben Pfaff Guest

    n869.pdf should work fine as a C reference manual. You just need
    to read it carefully.
     
    Ben Pfaff, Dec 9, 2005
    #9
  10. Michel Rouzic

    Flash Gordon Guest

    I would recommend reading the FAQ and getting a copy of K&R2.
     
    Flash Gordon, Dec 9, 2005
    #10
  11. A good tutorial is K&R2 (Kernighan & Ritchie_, _The C Programming
    Language_, 2nd Edition). A good reference is H&S5 (Harbison & Steele,
    _C: A Reference Manual_, 5th Edition).
     
    Keith Thompson, Dec 9, 2005
    #11
  12. yes it's good, I mostly search in it for descriptions of functions,
    but for such a thing as %0*d, I have no idea how I could have found it
    in it
     
    Michel Rouzic, Dec 9, 2005
    #12
  13. I see that the K&R2 is from 1988. Isn't it a bit outdated, since I tend
    to stick to C99, as it was made even before the C89?
     
    Michel Rouzic, Dec 9, 2005
    #13
  14. Michel Rouzic

    Ben Pfaff Guest

    You could have read the description of the fprintf function.
     
    Ben Pfaff, Dec 9, 2005
    #14
  15. K&R2 is based on a draft of what became the C90 standard.
    You should also read the errata list at
    <http://cm.bell-labs.com/cm/cs/cbook/2ediffs.html>.

    It doesn't cover C99, but then most compilers don't either. A number
    of compilers support *some* of the C99 extensions, but very few
    support all of them. It's up to you to decide whether a given C99
    feature is useful enough that you can risk the possible
    non-portability.

    C99 is very nearly upward compatible with C90 (even more so with
    well-written C90 that avoids things like implicit int) , so if you
    stick to what K&R2 tells you, your code should work with any C90 or
    C99 compiler.
     
    Keith Thompson, Dec 9, 2005
    #15
  16. well, I just looked the whole description of this function (which cover
    several pages) and couldn't even find it, although I knew precisely
    what I was looking for. You know when you're looking for such an info
    it's not obvious to tell yourself "How am I gonna find out how to print
    that? i know! i'm gonna read the 7 pages of the fprintf function, the
    answer will surely be there" well of course you can read those pages
    just by curiosity and find that out but when you're looking for
    something precise you won't do that...
     
    Michel Rouzic, Dec 10, 2005
    #16
  17. Michel Rouzic

    Michael Mair Guest

    Well, the text tells you about flags, precision, fieldwidth, length
    modifiers, and conversion specifiers. The latter are mandatory.
    So, once again: Is 0 a flag? Yes
    Next one: Is * in this case a fieldwidth or a precision? You can answer
    that one yourself. As there is no length modifier and the d conversion
    specifier, you should be able to figure out what it does.
    If you are not, you may be more happy with the C99 library reference
    provided to the public by dinkumware.com (this is a resource
    I appreciate very much) -- there is no shame in this; you have to
    understand "Standardese" and know C and the capabilities of the
    library to some extent to make full use of N869 or one of the other
    public drafts.

    If this is not enough, get a paper reference book. Maybe others can
    give you the title of a book appropriate to your needs.

    Another way is searching the clc archives. I/O, especially the
    formatted variety, comes up around here very often.


    Cheers
    Michael
     
    Michael Mair, Dec 10, 2005
    #17
  18. I for quick reference on the fly when I am looking for certain
    functionality, I find O'Reilly's Pocket C Reference Guide to be very
    useful.

    - Arctic
     
    Arctic Fidelity, Dec 10, 2005
    #18
  19. Michel Rouzic

    Malcolm Guest

    Some computer documentation is appalling.
    What the computer wants and needs is some sort of formal grammatical
    description of the printf string (maybe a regular expression or a yacc
    grammar).

    Some people think that, therefore, it is also appropriate to provide the
    user with such a description. Of course the computer and the human
    understanding of the function are two different things. Humans can easily
    extrapolate from examples of usage to the grammar, whilst computers find
    this very difficult.
     
    Malcolm, Dec 10, 2005
    #19
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