Custom "compile" loop

I have a custom compiler that I need to run on a set of files in a 
directory.  This is a straightforward process where aaaaa.src ---> 
aaaaa.out.

I have found the examples using a FOR task to process *.src --> *.out, 
and I'm familiar with the upToDate task to check if srcDate after 
outDate.  But I can't  find any examples where these both are used 
together.  The upToDate task doesn't seem to work in a loop.

I'm looking for an example of how to compile 1 src out of 100 if only 
that one src file has changed (basically exactly what javac does on 
.java-->.class compile... but I need to run an Exec task on the src 
instead of javac).

Can someone give me advice on how to code a for loop and checking 
upToDate on each file?

Thx.

Jerry