You can't use an exe to return a value like in a function, but there are some workarounds, for instance, you can let your program do some processing and write something to a textfile, and let the calling program read that textfile (easiest solution).
You can also use shared memory or send messages to the calling program (the hard way...)
Please be more specific about what you want, maybe you can make an ActiveX exe to do what you want.