while

With much reading and practice I have become a bit familiar with writing
autolisp routines. Things I couln't do a year ago are now becoming quite
simple.
One thing, however I'm having trouble with is using "while" for loops. Can
anyone explain the "while" function and how it works, maybe with a couple of
examples.
I'm especially baffled by how it is used to read down a data list, looking
for info. Any help would be appreciated.

 

(while (some condition exists)
(do this)
(and do this)
(and this...)
);; end while

"Some condition" can be T or nil, an equality, or whatever. For example:

(setq counter 10)
(while (> counter 0)
(princ (strcat "\n" (atoi counter)))
(setq counter (1- counter))
);; while
(princ)

As for your "data list" if it's in the form of a LISP list, you can use the
counter variable to get the "nth" element of the list, as in (setq dat (nth
datalist counter)) and so on.

If you're reading data from a file, all you have to do is to verify that
there's another element available:

(while (setq dat (read-line infile))
(do things)
(do more stuff)
)

(read-line ...) returns nil after it passes the last element of the file,
exiting the loop.
___

 

Thanks Paul. That was very simple yet concise. It will help a great deal.
Thanks again.