Thur, 12th Nov 2015, 23:55 Re: Programming Lab Stack Execution Question

A student writes:

> Dear Dr. Patt,
> I was working on the upcoming programming assignment earlier when I noticed
> in your instructions you noted that the status (success or failure) of the
> stack execution of the equation should be stored into R5. I can understand
> why this is a necessity, but I don't understand how to write this. Is there
> something that will be unique to a successful execution that a failed
> execution lacks or vice versa? Any clarification would be appreciated.
> Thanks!
> <<name withheld to protect the student who asks what's unique about a successful execution>>

  If you do not try the extra credit, you will assume (as we said) that all
  input strings are properly formed and you will never get a failure.  If you
  try the extra credit, then you need to detect bad strings.  If you try to
  process a bad string, the push or pop will fail to work properly.  Now a
  question for you: Why would an improper string not allow your program to
  properly evaluate it.  A simple example of an improper string should show
  you the problem.

  Good luck.

  Yale Patt