This example shows how one process can "call" another process
and have the "called" process do a calculation and then return
a result to the "calling" process.

The program use-adder.exe "calls" the adder.exe program as
if it were a kind of "external function". The use-adder process
passes parameters to the adder process by the command-line
method of inter-process communication. The adder process passes
its result back to use-adder using its standard output stream.
use-adder calls a function that lets it read as input what adder
wrote as output to its standard output stream. This is a simple
form of I/O redirection.