Changing Figure Numbering depending on how many occur in an \item

Question

While trying to typeset examination papers in LaTeX, I've become the victim of shifting figure numbering standards laid down by my institution.

The old way required figures to be numbered like this:

\renewcommand{\thefigure}{\theenumi\ifnum\value{figure}>1/\Alph{figure}\fi}

which is to say Figure Q1, Figure Q1/B, Figure Q1/C, etc. (the A omitted on the first figure). Now we have to put the '/A' on the first figure, but if there's only one figure per question, leave the '/A' out all together. Questions are in an enumerated list at the top level; hence the \theenumi above.

So now, if Q2 had one figure, it would be Figure Q2. If it were followed by Q3 with two figures, they would be Figure Q3/A and Figure Q3/B.

Answer 1

Here's one possible way to achieve this:

\def\@multiqprefix{@MultiFig}
\def\@multiq#1{\gdef\expandafter\noexpand\csname\@multiqprefix#1\endcsname{multifig}}
\def\@ifNotMultiQ#1{\expandafter\if#1\relax}
\def\@subfigpart#1#2{\@ifNotMultiQ{\csname\@multiqprefix\Roman{#1}\endcsname}\else{/\Alph{#2}}\fi}
\renewcommand{\thefigure}{\theenumi\@subfigpart{enumi}{figure}}
\AtEndEnvironment{figure}{
  \ifnum\value{figure}=2\immediate\write\@auxout{\@multiq{\Roman{enumi}}}\fi
}

It works by subverting the figure environment. When a second figure is supplied for a given question (the figure counter is used per question in this context, so I'm testing for its value being 2), a control sequence gets written in the aux file of the form

\gdef @MultiFigI {multifig}

where the trailing I corresponds to the question number in roman numeral form. Arabic numerals make it harder because they aren't normally allowed in control sequences, and there would no doubt be a load of \csnames all over the place if I went that way. {multifig} is a placeholder. Its value is never used, but it might come in handy one day.

\thefigure is overridden to test whether the current question is in fact a multi-figure one, and if it is, supplies the trailing \A, \B etc for all of the figures in the question.

My biggest hang-up was getting \@multiq right. Without the \expandafter\noexpand, the file would read first but on the second pass, you'd get items in the aux file like

\gdef multifig {multifig}

because the \@MultiFig would get expanded as it was written.

This solution has the following issues:

• It adds etoolbox as a required package
• It means you need three passes of the latex file to get the references right (but the tool I use to build the document, Kile, sorts this out automatically)