Help with implicit rule used in various directory compiling

[Nick Ng]

Hi there:

I have some simple questions on how to use GNU make to browse through
various sub-directory to compile using one and only one implicit rule.
I have a directory tree in my development env. like:
        src -
                prg1
                prg2
                prg3

Where all of source file (C) are stored in 3 different sub-dirs. If I
defined the implicit rule like:

%.o : %.c
        $(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@

Can anyone please tell me how to ask make to browse through each of these
sub-dirs and apply the implicit rule on it. I understood a PHONY target can
be a good starting point to kick off multiple target build. Any help is
appreciated :) :) !