[Year 12 SofDev] Sample Exam Questions

Tue May 3 16:04:39 EST 2011

I join Andrew in being glad that I am not teaching SD this year. Hope we
get some real guidance before the end of the year. I know and appreciate
all that Paula does and am sure that Claudia will do as well but we are
getting into all kinds of excessive details and relatively new things.
My training predates UCD's so I had never heard of them before the study
design.

John

From: Andrew Shortell [mailto:shortell at get2me.net] 
Sent: Sunday, 1 May 2011 7:02 PM
To: Year 12 Software Development Teachers' Mailing List
Subject: Re: [Year 12 SofDev] Sample Exam Questions

Hi Y'all

I really believe this indicated the teaching (and understanding of the
teaching) that goes on in classrooms.

At what point are we satisfied that teachers actually understand what
they are teaching, are on the right "track", are NOT GUESSING, and
really spend time to make sure their students understand really deep
material that is referenced in only one (or two) KK.

I would because I like the concepts of stacks - and the difference
between FIFO and LIFO, cells that have been previously populated with
what is now GIGO  etc etc.

But given that this is quite deep for year 12 level students (or was
until this study design) I would have moved on in the face of
incomprehension.

Now we cannot.

So how do we raise the level of knowledge of teachers so that they do
NOT LET DOWN the trust of their students..?????

It is very obvious that we do not all have the same level of
understanding... and hello to the 500 "readers who are too scared to
post or do not feel confident in their opinions". One MIGHT presume that
they are not posting because they are following the discussion in the
hope of figuring out what it all means?

even the current Cert IV in IT does not include material like this that
I have found!  (NOTE my careful caveat!)

I am just glad I am not teaching SD this year given the level of
confusion in what a question like this might mean...!

Andrew

ps even in VB, stacks (lists etc) start at zero but we can safely ignore
that in a windoze environment

Andrew Shortell

Heidelberg Teaching Unit in 2011

On 01/05/2011, at 5:57 PM, Robert Hind wrote:

Hi all!

I have never taught SD. Stopped with CS way back. This has sent me way
back to old texts - 70s and 80s

How about we ignore the bold entries in the original question and read
it to mean that the stack is

92

75

23

83

52

and the Top-of-stack pointer = 1, ie the value 52.

This is what the question seems to say.

We then proceed through the steps as given in the question

Start    Push (23)    Push (18)    Pop    Push (75)    Push (92) Push
(47)

92            92               92            92          92
92            *47

75            75               75            75          75
*92            92

23            23               *18           18         *75
75             75    

83            *23               23           *23         23
23            23

*52            52               52            52         52
52            52

Where * indicates the top-of-stack pointer

So where is the problem? Except perhaps in the way the question has been
written.

Robert Hind (Semi-retired) OOF, GOM
Ashwood and Traralgon
robert at yinnar.com

John Schwartz
Parade College
1436 Plenty Road
Bundoora, Victoria, 3083
Phone: 03 9468 3300
Fax: 03 9467 3937
e-mail: jschwartz at parade.vic.edu.au | web: www.parade.vic.edu.au

This e-mail and any attachments may be confidential. You must not disclose or use the information in this e-mail if you are not the intended recipient. If you have received this e-mail in error, please notify Parade College on (03) 9468 3300 immediately and delete the e-mail and all copies. Parade College does not guarantee that this e-mail is virus or error free. The attached files are provided and may only be used on the basis that the user assumes all responsibility for any loss, damage or consequence resulting directly or indirectly from the use of the attached files, whether caused by the negligence of the sender or not. Any views expressed in this e-mail are the views of the individual sending the message, and do not necessarily reflect the views held by Parade College.
	----- Original Message ----- 

	From: Mike Brookes <mailto:mikebr at tpg.com.au>  

	To: Year 12 Software Development Teachers' Mailing List
<mailto:sofdev at edulists.com.au>  

	Sent: Sunday, May 01, 2011 4:56 PM

	Subject: Re: [Year 12 SofDev] Sample Exam Questions

	G'Day again

	Whilst 'tis true that this question on the end of year exam
would unduly stress the little dears, to play devil's advocate, it does
have a useful function as a sample to provoke discussion about what
assumptions must be made. i.e. for the question to have a non trivial
answer, what assumptions are necessary? 

	Firstly the memory locations used for the stack do not have to
be initialised to 0 or any other value when the stack is created. The
pointer is the only thing that must be initialised.

	If you assume the stack starts at 1 instead of 0, then the stack
will not be full after step 6 reducing the value of the question.

	I also assumed that the bottom two values were in bold for a
purpose, the most obvious (at least to me) being that they were valid
existing members of the stack. 
	At the start of the question the stack is not full, the TOS
pointer is 1, the stack would be full when it reaches 4, so the non-bold
values were from previous uses of the stack. NB. a pop does not delete
the value from the stack, it just changes the TOS pointer.

	It may well be that a different set of assumptions will produce
a meaningful answer, these were the first consistent set I thought of.

	If you assume an empty stack at the start then, given that the
pointer is 1 at the start of the question, the TOS pointer must point to
the next available location (closer to convention) and the numbering
must start at 1 instead of 0.  In this case the stack is not full after
step 6 so another push step would be needed in the question.

							Stack at start
and after each step

Step

Function

Top

Output

			Start

Step 1

Step 2

Step 3

Step 4

Step 5

Step 6

1

Push (23)

2

Item added (23)

	Stack position

5

92

92

92

92

92

92

92

2

Push (18)

 3

Item added (18)

	4

75

75

18

18

75

75

47

3

Pop

2

Item removed (18)

	3

23

23

23

23

23

92

92

4

Push (75)

 3

Item added (75)

	2

83

83

18

18

75

75

75

5

Push (92)

4

Item added (92)

	1

52

23

23

23

23

23

23

6

Push (47)

5 

Item added (47)

						Top

1

2

3

2

3

4

5

	One would hope that a "real" question would at least have
numbered the stack positions and provided a key to explain what the bold
signified. A question to sort sheep from goats????????????

	Mike

	1

	On 1/05/2011 12:12 AM, Kevork Krozian wrote: 

	Hi Mark and Mike,

	  I am a little late on the scene but have to support Mark here.

	The question on stacks is more a puzzle than a reasonable
problem for a student to solve in limited time.

	The question begins with a picture of a stack to consider.......
which suggests the starting position of the problem. Apparently it is in
a full state .... and that can be determined from ?????

	Then, a push (23) is introduced. Hang on, I thought we had a
stack to consider with 5 elements. Are we adding another 23 or picking
up half way through the introduced stack ? 

	Where is it suggested that the introduced stack is in a "stack
full" state ? 

	The push and pop operations are not the problem, just the
starting position of the problem. When is the beginning is what got me
first.  The bold items were no help as I didn't consider them to be
significant.

	Also, the item Top (1) might mean top of stack to the writer,
but only adds to the confusion as it is not obvious it means the top of
the stack when we start with a stack with 5 elements. 

	I have gone through my 2nd year Data Structures textbooks and
have a strong recollection of the 1982 exams I did ( why wouldn't I ?? )
on stacks and data structures and there was always a pointer or arrow
(with a value in a variable ) showing the top of a stack at the
beginning of a question and the requirement was to draw the stack
through the various states after push and pop functions. Apart from that
we either have empty or full states. 

	I can't see how  this question would have helped in any way to
show student's understanding of a stack and its functions.

	Kind Regards

	Kevork Krozian

	Edulists Creator Administrator

	www.edulists.com.au <http://www.edulists.com.au/> 

	tel: 0419 356 034

	From: sofdev-bounces at edulists.com.au
[mailto:sofdev-bounces at edulists.com.au] On Behalf Of Mark KELLY
	Sent: Wednesday, 27 April 2011 2:36 PM
	To: Year 12 Software Development Teachers' Mailing List
	Subject: Re: [Year 12 SofDev] Sample Exam Questions

	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:

							Stack at start
and after each step

Step

Function

Top

Output

			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

						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

	_______________________________________________
	http://www.edulists.com.au <http://www.edulists.com.au/>  - FAQ,
Subscribe, Unsubscribe
	IT Software Development Mailing List kindly supported by
	http://www.vcaa.vic.edu.au <http://www.vcaa.vic.edu.au/>  -
Victorian Curriculum and Assessment Authority and

http://www.vcaa.vic.edu.au/vce/studies/infotech/softwaredevel3-4.html
	http://www.vitta.org.au <http://www.vitta.org.au/>   - VITTA
Victorian Information Technology Teachers Association Inc

	-- 
	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 <http://vceit.com/> 
	Moderator: IT Applications Edulist

	All generalisations are false, except this one.

	_______________________________________________
	http://www.edulists.com.au <http://www.edulists.com.au/>  - FAQ,
Subscribe, Unsubscribe
	IT Software Development Mailing List kindly supported by
	http://www.vcaa.vic.edu.au <http://www.vcaa.vic.edu.au/>  -
Victorian Curriculum and Assessment Authority and

http://www.vcaa.vic.edu.au/vce/studies/infotech/softwaredevel3-4.html 
	http://www.vitta.org.au <http://www.vitta.org.au/>   - VITTA
Victorian Information Technology Teachers Association Inc

________________________________

	_______________________________________________
	http://www.edulists.com.au - FAQ, Subscribe, Unsubscribe
	IT Software Development Mailing List kindly supported by
	http://www.vcaa.vic.edu.au - Victorian Curriculum and Assessment
Authority and

http://www.vcaa.vic.edu.au/vce/studies/infotech/softwaredevel3-4.html 
	http://www.vitta.org.au  - VITTA Victorian Information
Technology Teachers Association Inc

________________________________

_______________________________________________
http://www.edulists.com.au - FAQ, Subscribe, Unsubscribe
IT Software Development Mailing List kindly supported by
http://www.vcaa.vic.edu.au - Victorian Curriculum and Assessment
Authority and
http://www.vcaa.vic.edu.au/vce/studies/infotech/softwaredevel3-4.html 
http://www.vitta.org.au  - VITTA Victorian Information Technology
Teachers Association Inc

_______________________________________________
http://www.edulists.com.au - FAQ, Subscribe, Unsubscribe
IT Software Development Mailing List kindly supported by
http://www.vcaa.vic.edu.au - Victorian Curriculum and Assessment
Authority and
http://www.vcaa.vic.edu.au/vce/studies/infotech/softwaredevel3-4.html 
http://www.vitta.org.au  - VITTA Victorian Information Technology
Teachers Association Inc

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.edulists.com.au/pipermail/sofdev/attachments/20110503/bbdcf2da/attachment-0001.html 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/gif
Size: 8273 bytes
Desc: not available
Url : http://www.edulists.com.au/pipermail/sofdev/attachments/20110503/bbdcf2da/attachment-0001.gif 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/jpeg
Size: 81508 bytes
Desc: not available
Url : http://www.edulists.com.au/pipermail/sofdev/attachments/20110503/bbdcf2da/attachment-0001.jpe 