Pascal language (pointer) problem - Printable Version
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Pascal language (pointer) problem - sealfin - Oct 2, 2012 05:27 AM
Greetings, as part of a (sub-degree level) course I'm studying I'm revising Pascal (having last touched the language in, I think, 2001...), as the examinations which are part of the course often present questions – or expect questions to be answered – in a Pascal-esque language. I'd been working through the programming exercises in TURBO Pascal : An Introduction to the Art and Science of Programming (Second Edition) by Walter J. Savitch without issue, but I've now encountered a programming exercise which has revealed a gap in my understanding of pointers in Pascal:
On page 688 Walter J. Savitch Wrote:12. Write a procedure that takes a (singly) linked list and reverses the order of the nodes in the linked list. For concreteness, make it a linked list of characters.
So I threw together a solution to the programming exercise:
But when the procedure p_ReverseLinkedList is passed a linked list containing the sequence "Mark", the linked list becomes just "k". After a frustrating time trying (and failing) to identify the error in my logic, I threw together a C (rough) equivalent of my solution to the programming exercise to test my logic:
The function p_ReverseLinkedList works without error – when passed a linked list containing the sequence "Mark", the linked list becomes "kraM" – so it looks like my logic is correct.
And... I don't understand why my original Pascal solution to the programming exercise fails to function as expected; it looks like whilst p_current is treated as a variable parameter (correct), the m_next attribute of p_current is treated as a value parameter (incorrect); could somebody more fluent in Pascal please suggest where I'm going wrong...?
Nb. I'm using CodeWarrior.
RE: Pascal language problem - Skorche - Oct 2, 2012 08:38 AM
Hmm. I can't seem to find where the user list went to in the redesign.
You should search out Ingemar. He's a bit of a Pascal wiz. Still uses Free Pascal last I heard.
RE: Pascal language problem - sealfin - Nov 26, 2012 09:18 AM
Just to add a tiny elaboration: I'm not sure if it is relevant, but the project settings have two deviations from the default ANS Console 68k project settings: ANS Conformance is turned off and the IO Model is set to Turbo Pascal.
RE: Pascal language (pointer) problem - sealfin - Nov 27, 2012 04:38 AM
Huzzah, thanks to jareds of the xkcd forums I know now where I was going wrong