Custom numbering of listings

Question

I have a number of listings in my document, numbered 1, 2, 3 and so on. I need a table with three listings (say, three different variants of the same algorithm), that will be numbered as 2a, 2b, 2c. The very next listing would be numbered as 3.

Answer 1

you can also save the current counter value to make it independent from the current counter setting.

\documentclass{article}
\usepackage{listings}
\begin{document}

\begin{lstlisting}[caption=foo]
 foo
\end{lstlisting}

\setcounter{lstlisting}{0}
\renewcommand\thelstlisting{2.\alph{lstlisting}}
\begin{lstlisting}[caption=foo]
 foo
\end{lstlisting}
\begin{lstlisting}[caption=foo]
 foo
\end{lstlisting}
\begin{lstlisting}[caption=foo]
 foo
\end{lstlisting}

\renewcommand\thelstlisting{\arabic{lstlisting}}
\setcounter{lstlisting}{2}
\begin{lstlisting}[caption=foo]
 foo
\end{lstlisting}

\end{document}