Latex dashed box

\documentclass[12pt]{article}

\usepackage{graphics,color}

\begin{document}

\begin{flushleft}
\begin{picture}(100,100)
\dashbox{1}(100,100){a} 
\end{picture}
\begin{picture}(200,100)
\dashbox{1}(100,100){a} 
\end{picture}

\end{flushleft}

\linebreak
\begin{tabular}{ c c }
\dashbox{1}(100,100){a} &
\dashbox{1}(100,100){a}  \\
\end{tabular}


\end{document}