Using an IF statement to concatenate a string and a number

I'm working with a LaTeX screenplay documentclass document that has a slide counter in a newcommand that I wrote"

\newcommand{\slide}[1]{ \stepcounter{slidecounter} \newpage \begin{center} \underline{\textbf{Slide \arabic{slidecounter}}} \end{center} \rule{6in}{0.01in} \par
#1 }

This works perfectly for my purposes. But now I'd like to modify it so that it is something like:

\newcommand{\slide}[1]{ \stepcounter{slidecounter} \newpage \begin{center} \underline{\textbf{Slide \arabic{slidecounter}}} \end{center} \rule{6in}{0.01in} %% If slidecounter < 10 then "00" + slidecounter = ctr Else if slidecounter >= 10 & slidecounter < 100 then ctr = "0" + slidecounter Else ctr = slidecounter %% \par\bigskip \begin{center} \fbox{\includegraphics[scale=0.50]{"Page_"ctr.png}} \end{center}
\par
#1 }

The "Page_###.png" is a numbering scheme for identifying image files such as Page_010.png, Page_099.png, Page_109.png.

How do I write the If clause to accomplish this?

Thanks,

Walt Paczkowski