Just for fun, I have set up a code generator web page.  You put in an infix
expression like This*(That+23) and it writes PIC code to evaluate the
expression.  It's only 8 bits at this time.

http://niobrara.com/mks/evaluate8.html

If you want to see the previously discussed 2's complement in action, try, for
instance:

-(A+B)

I won't apologize here for the inefficiency of the generated code.  There's
enough of that on the web page ;)  Do let  me know if it actually generates
incorrect results.

- Mark Sullivan -