How to change equation numbering style

Question

Here is my MWE:

\documentclass[a4paper, 12pt]{report}
\usepackage{amssymb, amscd}
\begin{document}
    \chapter{Test}

    \begin{table}[h]
        \center
        \caption{Test}
        \begin{tabular}{l | r}
            Two & 2 \\
            Four & 4
        \end{tabular}
    \end{table}

    Test equation:
    \begin{equation}
        a+b=c^2
    \end{equation}
\end{document}

It produces this:

Now I would like to change equation numbering style. I want (1-1) instead of (1.1). How can I do that? Also, I want to preserve numbering style for tables and figures (Table 1.1:) , I don't want (Table 1-1:)

Answer 1

I was looking for some hints in the amsmath documentation and found the following trick (adapted, of course):

\usepackage{amsmath}
\renewcommand{\theequation}{\thechapter--\arabic{equation}}

If we look at the original definition of \theequation, we can find that it's more robust than our first attempt:

\long macro:->\ifnum \c@chapter >\z@ \thechapter .\fi \@arabic \c@equation

we can easily redefine it accordingly:

\makeatletter
\long\def\theequation{\ifnum \c@chapter > \z@ \thechapter --\fi \@arabic \c@equation}
\makeatother

Interestingly enough, there's another approach with the etoolbox package:

\usepackage{etoolbox}
\patchcmd{\theequation}{.}{--}{}{}

There we go. :)