A given program is written in one or the other of these two dialects.
The program stands a chance to work on most any machine if it is
compiled with the proper dialect. It is unlikely to work at all if
compiled with the wrong dialect.
It depends on the program, and whether or not chars in the user's
character set is sign extended (ie, in the USA, you likely won't notice
a difference between the two if chars just hold character values).
You might notice if a -1 (EOF) becomes a 255 and you get an infinite
loop in return (it did bite me). Of course, this is a bug in that
outside the US a 255 character might become an EOF.
Paolo
