Format page numbers

Question

How can I control look of the page numbers? For example, in the MWE below:

\documentclass[12pt]{article}
\usepackage[backend=biber]{biblatex}
\usepackage{fancyhdr}
\usepackage[top=2.54cm,bottom=2.54cm,left=3.81cm,right=2.54cm]{geometry}
\usepackage{setspace}
\doublespacing
\pagenumbering{roman}
\setcounter{page}{11}

\begin{document}
\begin{flushright}
    \begin{singlespace}
        John Doe \\
        March 2012 \\
        Department of Computer Science \\
    \end{singlespace}
\end{flushright}
\begin{center}
    Some Generic Title \\
\bigskip
    \textbf{\underline{Abstract}}
\end{center}
\vspace{-13pt}
Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah
Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah
Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah.

Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah
Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah
Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah.

Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah
Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah
Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah.

\end{document}}

I would like to have the page number look like:

-xi-

instead of:

xi

Answer 1

In your example, replace (loaded before geometry)

\usepackage{fancyhdr}

with (loaded after geometry)

\usepackage{fancyhdr}
\pagestyle{fancy}
\fancyfoot[C]{--~\thepage~--}

\fancyfoot[C]{--~\thepage~--} ("C" stands for "centered") will change the formatting of the page number in the footer as desired. (\pagestyle{fancy} is simply necessary to activate the features of the fancyhdr package; loading fancyhdr after geometry is needed to make fancyhdr recognize the margin changes effected by geometry.)

Note that redefining \thepage itself by, e.g., writing

\renewcommand*{\thepage}{--~\roman{page}~--}

is a bad idea because this will also affect the page number format in, e.g., cross-references.

\documentclass[12pt]{article}
% \usepackage[backend=biber]{biblatex}
\usepackage[top=2.54cm,bottom=2.54cm,left=3.81cm,right=2.54cm]{geometry}
\usepackage{fancyhdr}
\pagestyle{fancy}
\fancyfoot[C]{--~\thepage~--}
\usepackage{setspace}
\doublespacing
\pagenumbering{roman}
\setcounter{page}{11}

\begin{document}
\begin{flushright}
    \begin{singlespace}
        John Doe \\
        March 2012 \\
        Department of Computer Science \\
    \end{singlespace}
\end{flushright}
\begin{center}
    Some Generic Title \\
\bigskip
    \textbf{\underline{Abstract}}
\end{center}
\vspace{-13pt}
Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah
Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah
Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah.

Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah
Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah
Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah.

Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah
Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah
Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah Blah.

\end{document}