How to left-pad an integer with zeroes to make it many digits?

Question

A minimal working sample should be give first:

\documentclass{article}
\newcounter{mynumber}
\makeatletter 
\AtEndDocument{%
    \immediate\write\@auxout{%
        \string\setcounter{mynumber}{\number\value{mynumber}}%
    }%
}
\makeatother
\AtBeginDocument{%
    \stepcounter{mynumber}
}

\begin{document}
the version number is \themynumber.
\end{document}

Compiling it with XeLateX, we will get the version number such as 1. Then my QUESTION is

• how to make 1 become 0001 and 23 become 0023 and so on (i.e., four-digit numbers)? Note that I want the format like 0001 but not 0 001 (i e., no unit, no space).

Answer 1

with package siunitx:

the version number is \num[minimum-integer-digits = 4]{\themynumber}.

and for Sans Serif

\textsf{\num[detect-family,minimum-integer-digits = 4]{\themynumber}}.

Answer 2

Perhaps the fastest (and fully expandable, if that matters) solution, without additional packages:

\zeropad{<template>}{<integer>}
% <template> string of zeros defining desired width of output

\documentclass{article}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newcommand\zeropad[2]{%
  \ifnum#2<0\relax%
    {\ensuremath-}\zeropadA{#1}{\the\numexpr#2*-1\relax}%
  \else%
    \zeropadA{#1}{#2}%
  \fi%
}
\def\zeropadA#1#2{%
  \ifnum1#2<1#1
    \zeropadA{#1}{0#2}%
  \else%
    #2%
  \fi%
}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\newcounter{mynumber}
\makeatletter
\AtEndDocument{%
  \immediate\write\@auxout{%
    \string\setcounter{mynumber}{\themynumber}%
  }%
}
\makeatother
\AtBeginDocument{%
  \stepcounter{mynumber}
}

\begin{document}
the version number is \zeropad{0000}{\themynumber}

this is a negative number: \zeropad{0000}{-\themynumber}

expandibility check: \edef\foo{\zeropad{0000}{-\themynumber}}\foo
\end{document}

Answer 3

A fully expandable version

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\NewExpandableDocumentCommand{\padinteger}{mm}
 {
  \int_compare:nNnTF { #2 } < { 0 }
   {
    - \kuttens_padinteger:nn { #1 } { -#2 }
   }
   {
    \kuttens_padinteger:nn { #1 } { #2 }
   }
 }

\cs_new:Nn \kuttens_padinteger:nn
 {
  \prg_replicate:nn { #1 - \tl_count:f { \int_to_arabic:n { #2 } } } { 0 }
  \int_to_arabic:n { #2 }
 }
\cs_generate_variant:Nn \tl_count:n { f }
\ExplSyntaxOff

% define the macro based on the number of digits you need, here four
\makeatletter
\newcommand{\padfour}[1]{\expandafter\@padfour\csname c@#1\endcsname}
\newcommand{\@padfour}[1]{\padinteger{4}{#1}}
\makeatother

\newcounter{mynumber}
\renewcommand{\themynumber}{\padfour{mynumber}}

\makeatletter 
\AtEndDocument{%
    \immediate\write\@auxout{%
        \string\setcounter{mynumber}{\themynumber}%
    }%
}
\makeatother
\AtBeginDocument{%
    \stepcounter{mynumber}
}


\begin{document}

\section{The version number}

Number: \themynumber

\section{Other tests}

\newcounter{test}

\padinteger{4}{\value{test}}

\setcounter{test}{23}

\padinteger{4}{\value{test}}

%\padinteger{4}{12345} % would raise an error

\padinteger{8}{12345}

\setcounter{test}{-123}

$\padinteger{4}{\value{test}}$

\end{document}

Answer 4

Here's a LuaLaTeX-based solution, which uses Lua's built-in string.format function and sets up a user macro called \padnum. Note that the \padnum macro is fully expandable.

The default number of padding digits is 4; this can be overridden by supplying the number of padding digits as the optional argument of \padnum. The macro handles negative numbers without any issues, and it can be executed in both text mode and math mode.

% !TEX TS-program = lualatex

%% Create an external file to contain the Lua code
\RequirePackage{filecontents}
\begin{filecontents*}{padnum.lua}
function padnum ( digits , n)
-- The "0" term in string.format ensures left-padding with zeroes, as needed:
  tex.sprint ( string.format ( "%0"..digits.."d" , n ) )
end
\end{filecontents*}

\documentclass{article}
\directlua{dofile("padnum.lua")} % load the Lua function
% "\padnum" creates 4-digit numbers by default:
\newcommand\padnum[2][4]{\directlua{padnum(#1,#2)}}

\begin{document}
\newcommand\mynum{23}
\padnum{\mynum}, \padnum[6]{1}, $\padnum[2]{-100000}$, $\padnum{-11}$
\end{document}

Answer 5

@koleygr Thank you! In fact, I have ever tried your method before you told me but failed. Now I get the right one.

\documentclass{article}
\usepackage{numprint}
\newcounter{mynumber}
\makeatletter 
\AtEndDocument{%
    \immediate\write\@auxout{%
        \string\setcounter{mynumber}{\number\value{mynumber}}%
    }%
}
\makeatother
\AtBeginDocument{%
    \stepcounter{mynumber}
}
\newcommand{\myversionnumber}{\npfourdigitnosep\nplpadding{4}\numprint{\themynumber}}

\begin{document}
the version number is \myversionnumber.
\end{document}