Replacing dots with comma in `fp` result

Question

I am using fp to add a few values in LaTeX. How can I replace the . in \erg with a comma (In Germany the comma is used as decimal mark).

\documentclass{minimal}
\usepackage{fp}

\begin{document}

\FPset\erg{0} 
\FPadd\erg{\erg}{23.20} 
\FPadd\erg{\erg}{38.46}
\FPadd\erg{\erg}{22.36}
\FPadd\erg{\erg}{22.00}
\FPadd\erg{\erg}{15.00}
\FPclip\erg\erg

The sum is  \erg\

\end{document}

Answer 1

I'd use siunitx for the printing and the LaTeX3 FPU for the sums:

\documentclass{article}
\usepackage{siunitx}
\sisetup{locale = DE}

\ExplSyntaxOn
\newcommand*{\fpeval}[1]{\fp_eval:n {#1}}
\newcommand*{\addto}[2]{\fp_set:Nn #1 { #1 + (#2) }}
\ExplSyntaxOff
\begin{document}

\newcommand*{\erg}{0} 
\addto{\erg}{23.20}
\addto{\erg}{38.46}
\addto{\erg}{22.36}
\addto{\erg}{22.00}
\addto{\erg}{15.00}

The sum is  \num{\fpeval{\erg}}

\end{document}

Answer 2

\documentclass[preview,border=12pt,varwidth]{standalone}% change this line back to your own document class
\usepackage[nomessages]{fp}

\usepackage{siunitx}
\sisetup{output-decimal-marker={,}}

\begin{document}

\FPset\erg{0} 
\FPadd\erg{\erg}{23.20} 
\FPadd\erg{\erg}{38.46}
\FPadd\erg{\erg}{22.36}
\FPadd\erg{\erg}{22.00}
\FPadd\erg{\erg}{15.00}
\FPclip\erg\erg

The sum is  \num{\erg}

\end{document}