counterscross-referencing
I created a custom counter 'rtaskno' and a command '\rtask' as following:
\newcounter{rtaskno}
\newcommand{\rtask}{%
\stepcounter{rtaskno}%
\thertaskno}
I like to use them as following:
\section{Task \rtask. Blah Blah..}
\section{Task \rtask. Blah Blah..}
\section{Task \rtask. Blah Blah..}
\section{Task \rtask. Blah Blah..}
Later in the text, if I want to cross-reference 'Task 3', how can I do it? Where to put label?
With the package hyperref you can use the optional argument of \hyperref to reference a \label with arbitrary text:
\documentclass{article}
\usepackage{hyperref}
\begin{document}
\section{Hello World}
\label{sec:hello}
Reference to \hyperref[sec:hello]{this section}.
\end{document}
By default, \newcounter{hypothese} will set the numbering style of the newly created hypothese counter to arabic (1, 2, 3,...). However, the numbering style can easily be changed. For instance, to set the style to capital letters (A, B, C,...), you should insert
\renewcommand{\thehypothese}{\Alph{hypothese}}
preferably right after defining the counter in question (see my code below). Two compilations might be required to obtain the desired result.
Side note: You can save yourself some hassle by avoiding hardcoding "hypothesis". With your current approach, if you decide, at a later stage, to change all cross-reference instances of "Hypothesis" in your document to "Assumption", you're in for some tedious and error-prone search & replace. A more maintainable alternative is to use the prettyref package and its \newrefformat and \prettyref commands; for instance, if you decide to substitute "Assumption" for "Hypothesis" throughout your document at a later stage, you can simply substitute Assumption for Hypothesis in the second argument of the \newrefformat command. The change will be reflected throughout the document. An even more powerful, albeit not as straightforward to use, package for that is cleveref.
\documentclass{article}
\usepackage{csquotes}
\setlength\parindent{0pt}
\usepackage{prettyref}
\newrefformat{hypo}{Hypothesis~\ref{#1}}
\begin{document}
\newcounter{hypothese}
\renewcommand{\thehypothese}{\Alph{hypothese}}
\refstepcounter{hypothese}\label{hypo:lenght_of_words}
Hypothesis~\thehypothese\\[1em]
\refstepcounter{hypothese}\label{hypo:blue_word}
Hypothesis~\thehypothese\\
I think thant the words will be longer in this condition
(\prettyref{hypo:lenght_of_words}) and that the word \emph{blue}
will be user more frequently than in the next situation (\prettyref{hypo:blue_word}).\\
% ... statistical computing
As predicted in \prettyref{hypo:blue_word}, the word \enquote{blue} is much more
used than in the natural condition.
\end{document}
Best Answer
There are tricky timing issues in your problem. If you are going to prepare a table of contents the thing as it is now will bomb out.
Probably the best thing to do is to use a two-pass strategy:
When you want to use the task number in your section titles you'll write