[Year 12 SofDev] Re: SD VITTA exam 2, multichoice #1

Wed Oct 17 09:45:26 EST 2007

Kevin
The way you describe it matches the theory I have seen over the years. However, the implementation of these constructs takes all forms. For example, I don't think VB.NET will traverse a FOR..NEXT loop even once if the start>finish, whereas I have used other versions of Basic in the past that had to traverse it at least once.

The following implementation of a a while loop that Mark Kelly found the other day, which is actually a Repeat..Until loop in your theoretical sense but using different key words, says it all....
Do
..
Loop While <condition>

Frank

	-----Original Message----- 
	From: sofdev-bounces at edulists.com.au on behalf of Kevin Feely 
	Sent: Wed 17-Oct-07 9:29 AM 
	To: Year 12 Software Development Teachers' Mailing List 
	Cc: 
	Subject: Re: [Year 12 SofDev] Re: SD VITTA exam 2, multichoice #1

	Hi Mark,
	For i= 1 to ... will set i to 1 and you will get at least 1 loop. for-next cannot be written (and why would you) so that you do not get the loop at least once..
	For next is an iteration construct
	The other 2 are conditional branching constructs

	So logically for-next is not a test but an iteration control - the other 2 are branching controls DESIGNED for testing. One when you will need to loop at least once, and the other in cases when the loop may not need to not execute at all.
	What do we have .......the 4 main programming constructs ...

	*	Sequence .... a series of line of code 

	*	Repetition (aka iteration or Loops) - where you would use for next or whatever the program uses for iterations

	*	Conditional Branching 
	*	Combined Branching and Repetition 

		*	Conditional test at start of the construct - the "while-do" 

		*	Conditional test at the end of the construct - the "repeat-until"

	(taken from http://www.tutorials4u.com/c/loopsdecisions.htm)

	Mark Kelly wrote: 

		Ah, but FOR..NEXT does test whether the index is beyond the specified boundaries. 

		e.g. FOR i = 1 to 5 

		is an implicit pre-test for i>5. 

		Cheers 
		Mark 

		Kevin Feely wrote: 

			Hi All, 
			I would approach the question with - is their a value for which this loop would NOT execute? 
			If it is a pre test condition then you will not get any processing from the lines within the loop, if it is a post test condition then the loop will execute AT LEAST ONCE. 
			Also i (that is me myself I mwa) accept that the logic of a do-while loop is to test the condition before the loop starts, and the repeat-until loop tests at the end of the loop (the construct within a language will vary BUT in generic terms i accept this "standard"), even though  the ACTUAL  written algorithm on the question is not perfect ( I suppose thats hard to do unless you write it in 9 diiferent languages, but then again it is supposed to be in pcode format and therefore language independent) 
			Also the for-next answer seems to be a bit of a distraction as it does not TEST for anything, it will simply loop as many times as you want, via a variable used as a counter,  and this could be from 0 times to a big number. 
			So i would think the expected answer was A 
			regards 
			kev 

			Sonia Cotugno wrote: 

				I agree with you Mark. 

				I answered with (C) For...Next because none of the others tested at the top of the loop. I think it's actually incorrect to say Do...While. I really do think it should have said While as an option. 

				Regards, 
				Sonia Cotugno 

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				*Subject:* sofdev Digest, Vol 32, Issue 8 [Scanned] 

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				Today's Topics: 

				   1. SD VITTA exam 2, multichoice #1 (Mark Kelly) 

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				Message: 1 
				Date: Fri, 12 Oct 2007 11:59:09 +1000 
				From: Mark Kelly <kel at mckinnonsc.vic.edu.au> <mailto:kel at mckinnonsc.vic.edu.au>  
				Subject: [Year 12 SofDev] SD VITTA exam 2, multichoice #1 
				To: "Year 12 Software Development Teachers' Mailing List" 
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				I'm curious what others think... 

				"Testing at the 'top of the loop' is performed by which syntax in 
				pseudo-code? 

				A. Do..While 
				B. Do..Until 
				C. For..Next 
				D. EOF" 

				The suggested answer given is A, with the explanation that 'Do..Until is 
				often referred to as testing at the bottom of the loop...' 

				But surely both do..while and do..until both test at the bottom of the loop. 

				A While..Wend, on the other hand, tests at the top. 

				-- 

				Mark Kelly 
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