# Convert numbers in string to string

I store some strings in a variable \def\nomVAR{A12Z4E} and I want to create some other command using the content of \nomVAR. LaTeX doesn't accept to declare variable with number in its name. So the idea will be to convert all the number in the string using \numberstringnum command (fmtcount package). The xstring can extract some specific string in a string but I have to precise the position of each one.

Do you think it is possible to write a function to convert each number to a string in a string and to rebuilt it?

Thus A12Z4E will become AonetwoZfourE.

MNWE

\documentclass{minimal}

\usepackage{xstring}
\usepackage{fmtcount}

\begin{document}

\def\nomVAR {A12Z4E}

\nomVAR

\numberstringnum{1}

\numberstringnum{\nomVAR} %not working

\end{document}


SOLUTION (thanks egreg)

\documentclass{minimal}

\usepackage{xstring}

\begin{document}

\def\nomVAR {A12Z4E}

\nomVAR

\numberstringnum{1}

\newcommand{\changestep}[2]{%
\expandafter\StrSubstitute\expandafter{\x}{#1}{#2}[\x]%
}
\newcommand{\changeall}[1]{
% suppress expansions made by xstring
\StrSubstitute{#1}{0}{zero}[\x]%
\x
\noexpandarg
\changestep{1}{one}
\changestep{2}{two}
\changestep{3}{three}
\changestep{4}{four}
\changestep{5}{five}
\changestep{6}{six}
\changestep{7}{seven}
\changestep{8}{eight}
\changestep{9}{nine}
\x
}

\changeall{\nomVAR}

\end{document}

• With xstring it's easy to replace each 1 with one and so on. But I'm not seeing what's the aim of this. – egreg Nov 25 '15 at 12:56

You can do it expandably, provided the string has also alphanumeric ASCII characters:

\documentclass{article}

\makeatletter
\newcommand{\convertdigits}[1]{\expandafter\convert@digits#1\convert@digits}
\def\convert@digits#1{%
\ifx#1\convert@digits
\expandafter\@gobble
\else
\expandafter\@firstofone
\fi
{\convert@@digits#1}%
}
\def\convert@@digits#1{%
\ifnum9=9#1%
\expandafter\@gobble
\else
\expandafter\@firstofone
\fi
{\convert@@digit#1}\convert@digits
}
\def\convert@@digit#1{%
\ifcase#1%
zero\or
one\or
two\or
three\or
four\or
five\or
six\or
seven\or
eight\or
nine\fi
}
\makeatother

\begin{document}

\def\myvar{A12Z4E}

\convertdigits{A12Z4E}

\convertdigits{\myvar}

\edef\myvartext{\convertdigits{\myvar}}
\texttt{\meaning\myvartext}

\end{document}