I am trying to combine two packages in to a new command. The problem I have come across is when trying to add an optional parameter.
I want to be able to have 2 parameters with the second parameter being invoked if I use it but otherwise LaTeX should just use the first one.
I think I need something in "[???]" below but I don't know what.
\usepackage{mhchem}
\usepackage{chemnum}
\newcommand{\cecount}[2][???]{\ce{#2} (\cmpd{#1})}
\begin{document}
Reaction of compounds \ce{H2} and \ce{O2} makes \cecount[AAA]{H2O}.
Another compound is \cecount{X}.
Reaction of compounds Na and Cl makes \cecount[B]{NaCl}.
Compound \refcmpd{AAA} dissolves compound \refcmpd{B}.
But I can also refer to \refcmpd{X}
\end{document}
This gives me an error of (??) when trying to use the \refcmpd{X} command.
