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

[Michel Rouzic]

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

 

[jacob navia]

Michel Rouzic a écrit :

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

#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

 

[Mike Wahler]

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

#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

 

[David Resnick]

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

Try "%04d"

-David

 

[Ben Pfaff]

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

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

You should really get a C reference manual.

 

[Kleuskes & Moos]

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.

sprintf("%04d", some_int);

 

[Michel Rouzic]

#include <stdio.h>

int main()
{
int i = 0;

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

return 0;
}

Where's your textbook?

Thanks. Got no textbook. n869.pdf is all I got. Plus i'm learning C on
my own

 

[Michel Rouzic]

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

You should really get a C reference manual.

OK thanks. All i got is n869.pdf, otherwise I have nothing else. What
else should I get?

 

[Ben Pfaff]

OK thanks. All i got is n869.pdf, otherwise I have nothing else. What
else should I get?

n869.pdf should work fine as a C reference manual. You just need
to read it carefully.

 

[Flash Gordon]

OK thanks. All i got is n869.pdf, otherwise I have nothing else. What
else should I get?

I would recommend reading the FAQ and getting a copy of K&R2.

 

[Keith Thompson]

Ben Pfaff wrote: [snip]

You should really get a C reference manual.

OK thanks. All i got is n869.pdf, otherwise I have nothing else. What
else should I get?

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).

 

[Michel Rouzic]

n869.pdf should work fine as a C reference manual. You just need
to read it carefully.

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]

I would recommend reading the FAQ and getting a copy of K&R2.

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?

 

[Ben Pfaff]

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

You could have read the description of the fprintf function.

 

[Keith Thompson]

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?

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.

 

[Michel Rouzic]

You could have read the description of the fprintf function.

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...

 

[Michael Mair]

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...

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

 

[Arctic Fidelity]

OK thanks. All i got is n869.pdf, otherwise I have nothing else. What
else should I get?

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

 

[Malcolm]

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...

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.