ppindent.el

Download ppindent from
http://www.emacswiki.org/cgi-bin/emacs/ppindent.el

Example:

        #ifdef WOO
        ....
        #if defined(X) && !defined(Y)
        #ifdef Q8
        ...
        #else
        ...
        ....
        #elif defined (Z)
        ....
        #endif
        #endif
        #endif

After "M-x ppindent-c" becomes:

        #ifdef WOO
        ....
        #  if defined(X) && !defined(Y)
        #    ifdef Q8
        ...
        #    else
        ...
        ....
        #    elif defined (Z)
        ....
        #    endif
        #  endif
        #endif