Count number of succeeding sections within the text

Question

Writing about structure of the remainder of my article in the Introduction section, I want to dynamically get how many sections are left to the end of the manuscript.

So in case my article consists of six sections in total, I would need a command \foo once called within the body of the first section, renders to "five" and so on.

Answer 1

The following stores the value of the section counter minus 1 as a \label at the end of the document. It's then retrieved using a direct form of \ref and turned into a string using fmtcount.

\documentclass{article}

\usepackage{fmtcount,xfp}
\usepackage{lipsum}

\makeatletter
\AtEndDocument{%
  \def\@currentlabel{\inteval{\value{section}-1}}%
  \label{foolabel}%
}
\newcommand{\foo}{%
  \ifcsname r@foolabel\endcsname
    \expandafter\numberstringnum\expandafter{\expandafter\@firstoftwo\r@foolabel}%
  \else
    0%
  \fi
}
\makeatother

\begin{document}

\sloppy
\section{Introduction}
There are \foo{} remaining sections.

\section{First section}\lipsum[1-50]
\section{Second section}\lipsum[1-50]
\section{Third section}\lipsum[1-50]
\section{Fourth section}\lipsum[1-50]
\section{Fifth section}\lipsum[1-50]

\end{document}

Since it uses the \label-\ref system to extract the last sectional number, you need to compile twice with every change in the number of \sections (so the \references can settle).

---

If you're dealing with unnumbered sections and want to include them as well (typically a reference section), then you can use the following setup:

\documentclass{article}

\usepackage{fmtcount,xfp}
\usepackage{lipsum}

\newcounter{totsection}

\let\oldsection\section
\renewcommand{\section}{\stepcounter{totsection}\oldsection}

\makeatletter
\AtEndDocument{%
  \def\@currentlabel{\inteval{\value{totsection}-1}}%
  \label{foolabel}%
}


\newcommand{\foo}{%
  \ifcsname r@foolabel\endcsname
    \expandafter\numberstringnum\expandafter{\expandafter\@firstoftwo\r@foolabel}%
  \else
    0%
  \fi
}
\makeatother

\begin{document}

\sloppy
\section{Introduction}
There are \foo{} remaining sections.

\section{First section}\lipsum[1-50]
\section{Second section}\lipsum[1-50]
\section{Third section}\lipsum[1-50]
\section{Fourth section}\lipsum[1-50]
\section{Fifth section}\lipsum[1-50]
\section*{Sixth section}\lipsum[1-50]

\end{document}

It uses a different counter totsection that counts a section whether it's numbered or not.

Answer 2

EDITED to auto-calculate the number of sections in the document.

If you want the code to calculate the total number of sections, the refcount package can help. One can use an \AtEndDocument hook to set the label to capture the final section number.

\documentclass{article}
\usepackage{refcount}
\newcommand\sectionsleft{\the\numexpr 
  \getrefnumber{mylastsection}-\thesection\relax}
\AtEndDocument{\label{mylastsection}}
\begin{document}
\section{First}

My sections left are \sectionsleft.

\section{Second}

My sections left are \sectionsleft.

\section{Third}
\section{Fourth}
\section{Fifth}

My sections left are \sectionsleft.

\section{Last}

There are \sectionsleft{} sections remaining.
\end{document}

Answer 3

The package totcount does this with minimal intervention.

\documentclass{article}
\usepackage{totcount}

\regtotcounter{section}

\begin{document}

This paper consists of \total{section} sections.

\section{A}
\section{B}
\section{C}
\section{D}
\section{E}
\section{F}

\end{document}