Dynamically created program listing

Question

Is there a way to have a easy to change value in program listing? Something along these lines:

\newcommand{\variable}{2}

And then having somewhere

\begin{lstlisting}
...
i *= \variable;
...
\end{lstlisting}

I would like to keep the format, so I don't want to end and start another listing.

Answer 1

Yes. You should use the mathescape option provided by listings:

\begin{lstlisting}[mathescape=true]
...
i *= $\variable$;
...
\end{lstlisting}

This escapes back to LaTeX, where \variable has a different meaning than inside lstlisting. Here's a complete MWE showing the use:

\documentclass{article}
\usepackage{listings}% http://ctan.org/pkg/listings
\newcommand{\variable}{2}
\begin{document}
\begin{lstlisting}
...
i *= \variable;
...
\end{lstlisting}
\begin{lstlisting}[mathescape=true]
...
i *= $\variable$;
...
\end{lstlisting}
\end{document}