[Year 12 SofDev] Sample Exam Questions

[Mark KELLY]

Thanks for the bone, Mike.  Woof!  It finally let me work out the many
assumptions underlying the question: and after all that, I'm not wagging my
tail.

I think the question is far from clear, and I doubt students would make much
of it in a real exam.

- It does not, for example, say that the stack is zero-based.  If one
assumes (as I did) that the stack indexing starts at 1, the whole thing
changes and nothing makes sense.
- It does not indicate what the mysterious bolding of the bottom 2 items is
meant to represent.  If the examiners invent their own conventions, they
should explain them to us.
- It does not tell us that the stack pointer in updated *before* a push/pop
instead of being changed afterwards, as often happens.  Again, this changes
everything.
- One has to realise that the stack is expanding from the bottom and not
from the top. Stacks are often represented growing in either direction.

When it comes to real-world stack implementation, there are so many
different options such as these that I found the question mind-boggling
while I went through the permutations of possible readings.

Grrr.

On 21 April 2011 14:45, Mike Brookes <mikebr at tpg.com.au> wrote:

>  Hi Mark et Al
>
> For the question to make sense one has to make the assumption that the
> stack positions start at the bottom with position zero and go up to position
> 4 which is the top of the stack. At the start the bottom two (in bold on the
> PDF) are valid, hence the top of stack pointer showing 1.
>
> Below is the completed table and the stack at the start and after each
> step:
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>  Stack at start and after each step  Step Function Top Output
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>  Start Step 1 Step 2 Step 3 Step 4 Step 5 Step 6  1 Push (23) 2 Item added
> (23)
>  Stack position 4 92 92 92 92 92 92 92  2 Push (18)   Item added (18)
>  3 75 75 18 18 75 75 75  3 Pop 2 Item removed (18)
>  2 23 23 23 23 23 23 23  4 Push (75)   Item added (75)
>  1 83 83 83 83 83 83 83  5 Push (92) 4 Item added (92)
>  0 52 52 52 52 52 52 52  6 Push (47)   Stack full
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>  Top 1 2 3 2 3 4 4
> Mike Brookes
> Semi retired gentleman from Copperfield College
>
>
> On 21/04/2011 1:35 PM, Mark KELLY wrote:
>
> Would someone be kind enough to throw me a bone about the stack question -
> Q3?
>
> I thought I knew stack implementation from my assembly language days with
> Z80... this question feels like walking into someone's half-finished thought
> process.  I'm really confused about this.After half an hour of conjecture,
> I’ve tried four times to ask a series of sensible questions to make sense of
> it, and have failed every time.
>
>
>  The only apparent answer involves time travel, reversed arrays,
> irrelevant stack pointers and bogus bolding of stack items.  The
> relationship between the stack and the table is only the beginning of the
> problem...
>
>
>  I’d be delighted if anyone could walk me through this...
>
>
>  Regards
>
> Mark
>
>
>
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-- 
Mark Kelly
Manager of ICT, Reporting, IT Learning Area
McKinnon Secondary College
McKinnon Rd McKinnon 3204, Victoria, Australia
Direct line / Voicemail: +613 8520 9085, Fax +613 9578 9253
kel at mckinnonsc.vic.edu.au
VCE IT Lecture Notes: http://vceit.com
Moderator: IT Applications Edulist

All generalisations are false, except this one.
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