How to get figure counter to follow theorem counter?

Question

I am trying to get my figure to counter to follow my theorem counter. I created a few different environments: lemma, example, definitions, etc. I have gotten all of them to follow my theorem counter.

The numbering goes Chapter.Section.theorem. So it will go like this:

Chapter 2 "The Second Chapter"

Section 2.1 The First Section

Definition 2.1.1 - First Definition

Theorem 2.1.2 - The First Theorem

Section 2.2 The Second Section

Chapter 3 "The Third Chapter"

etc...

However, the figures don't seem to follow the counter. The first figure (in section 2.4) is number Figure 2.3 ... So I'm trying to get it to fall in line with the rest so that it would look like:

Example 3.2.5 - The Example

Figure 3.2.6 - The Figure for Example 3.2.5

Any suggestions? I put all the code that I think is applicable below. Let me know if you need more/something else...

\documentclass{thesis} %This is my school's self-made document class

\newtheorem{theorem}{Theorem}[section]
\newtheorem{corollary}[theorem]{Corollary}
\newtheorem{definition}[theorem]{Definition}
\newtheorem{lemma}[theorem]{Lemma}
\newtheorem{proposition}[theorem]{Proposition}

\theoremstyle{definition}   %Added by me
\newtheorem{example}[theorem]{Example}

%\makeatletter  %Added by me
%\let\c@theorem\c@figure
%\makeatother

\begin{document}

\begin{figure}
\caption{The Figure}
\end{figure}

\end{document}

I've attempted the \let\c@theorem\c@figure but that doesn't seem to work.

Answer 1

A proposition:

1. Don't use floating figures, remove \begin{figure}...\end{figure} around the graphics and caption
2. Use caption package and \captionof{figure}{foo text} instead of standard \caption command
3. Redefine the figure output command \thefigure to obtain the \thetheorem.\arabic{figure} output
4. (Optional) Use a resetting of figure counter by theorem, i.e. @addtoreset{figure}{theorem} If this is not wanted, just comment that line

---

\documentclass{book} % can't use thesis.cls here, since unknown!!!

\usepackage{caption}%
\usepackage[demo]{graphicx}%
\usepackage{amsthm}%

\newtheorem{theorem}{Theorem}[section]
\newtheorem{corollary}[theorem]{Corollary}
\newtheorem{definition}[theorem]{Definition}
\newtheorem{lemma}[theorem]{Lemma}
\newtheorem{proposition}[theorem]{Proposition}

\theoremstyle{definition}   %Added by me
\newtheorem{example}[theorem]{Example}

%\makeatletter  %Added by me
%\let\c@theorem\c@figure
%\makeatother

\makeatletter
\@addtoreset{figure}{theorem}
\makeatother

\let\StandardTheFigure\thefigure
\renewcommand{\thefigure}{\thetheorem.\arabic{figure}}

\begin{document}

\chapter{My first chapter}

\section{The very first section}%

\begin{theorem}
\( E = m c^2 \)
\end{theorem}

\begin{center}
\includegraphics{somefig}
\captionof{figure}{The Figure}
\end{center}

\begin{theorem}
\( E^2 = p^2 c^2 + \left({m c^2}\right)^2 \)
\end{theorem}

\begin{center}
\includegraphics{somefig}
\captionof{figure}{Another figure}%
\end{center}


\end{document}

Answer 2

I was searching for the same thing and the answer is a bit simpler I think. With my Method it doesn't matter if you use the figure environment or not.

1. You need to overwrite of the figure Counter to be a theorem counter:
   \renewcommand{\thefigure}{\thesection.\arabic{theorem}}
2. you need to raise the theorem counter by one before you use captionof or caption: \stepcounter{theorem} or \addtocounter{theorem}{1} \

\thefigure is calling on the figure counter and you basically overwrite the counter. \thesection is there for the 1.1, because the theorem counter is also displayed that way, and the \arabic{theorem} ist just printing the theorem counter. if you use a \begin{theorem} the counter automatically raises itself but it doesn't with figures, when you just call upon it, that's why you have to raise it yourself, when you use a figure. so in total:

\documentclass{book} % can't use thesis.cls here, since unknown!!!

\usepackage{caption}%
\usepackage[demo]{graphicx}%
\usepackage{amsthm}%

\newtheorem{theorem}{Theorem}[section]
\newtheorem{corollary}[theorem]{Corollary}
\newtheorem{definition}[theorem]{Definition}
\newtheorem{lemma}[theorem]{Lemma}
\newtheorem{proposition}[theorem]{Proposition}

\theoremstyle{definition}   %Added by me
\newtheorem{example}[theorem]{Example}

\renewcommand{\thefigure}{\thesection.\arabic{theorem}}%IMPORTANT

\begin{document}

\chapter{My first chapter}

\section{The very first section}%

\begin{theorem}
\( E = m c^2 \)
\end{theorem}

\begin{figure}[h]
\centering
\stepcounter{theorem}%IMPORTANT
\includegraphics{somefig}
\caption{The Figure}
\end{figure}

\begin{theorem}
\( E^2 = p^2 c^2 + \left({m c^2}\right)^2 \)
\end{theorem}

\begin{center}
\stepcounter{theorem}%IMPORTANT
\includegraphics{somefig}
\captionof{figure}{Another figure}%
\end{center}


\end{document}