[Year 12 SofDev] DLTV Exam 1
ATKINSON-BUCK, Damien
Damien.ATKINSON-BUCK at ivanhoe.com.au
Wed Oct 8 23:20:14 EST 2014
Thanks Alan/James
Damien Atkinson-Buck
Head of Learning Area: Technology/Arts
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From: alan whittaker [mailto:awhittaker at netspace.net.au]
Sent: Wednesday, 8 October 2014 10:08 PM
To: Year 12 Software Development Teachers' Mailing List
Subject: Re: [Year 12 SofDev] DLTV Exam 1
Hello there,
I think the issue is the Mod keyword in your VB code (somewhere around line 10). The pseudocode does state a "Mod()" function but I don't think it should be there (in other words I don't know what it is meant to do).
Mod gives you the remainder when the left number is divided by the one on the right,
therefore, no matter the values of low and high, this will always give you a value of 0 or 1 (when dividing by 2), which would explain your infinite loop.
ie: (1 + 999) Mod 2 = 1000 Mod 2
= 0
as the remainder when 1000 is divided by 2 is 0.
Given that Mod can only give you two values, your loop will never end as StudentNo(0) = 1 and StudentNo(1) = 125, neither of which are the searchnum.
Instead of finding the modulus of low + high, just dividing it by 2 will give the middle number between low and high, and I think will fix the loop.
Hope this helps
James son of an aging, once-an-IT-teacher, Alan Whittaker (Kept him off the games for a while)
On 08/10/2014, at 5:50 PM, ATKINSON-BUCK, Damien wrote:
Hi folks,
I'm just going through the DLTV Exam and can't quite figure the answer to the algorithm question 12 below.
<image002.png>
<image003.png>
My desk produces,
Pass
Middle
Low
High
Result
StudentNo(Middle)
1
0
1
999
False
1
2
1
0
999
False
125
3
0
1
999
False
1
4
1
0
999
False
125
AND SO ON
I've tried it as vb code below and ended in an infinite loop. Am I missing something blatantly obvious here or can anyone see the fix for this?
Module Module1
Dim StudentNo() As Integer = {1, 125, 250, 375, 500, 625, 750, 875, 999}
Sub Main()
Dim low As Integer = 1
Dim high As Integer = 999
Dim result As Boolean = False
Dim searchnum As Integer = 375
Do While low <= high And result = False
Dim middle As Integer = (low + high) Mod 2
If StudentNo(middle) = searchnum Then
result = True
Dim myMessage As String = "Low " & low & ", High " & high & ", Mid " & middle
MsgBox(myMessage, vbOK, "DONE")
End If
If StudentNo(middle) > searchnum Then
high = middle
Else
low = middle
End If
Loop
End Sub
End Module
Damien Atkinson-Buck
Head of Learning Area: Technology/Arts
p: +61 3 9490 3848
e: damien.atkinson-buck at ivanhoe.com.au<mailto:damien.atkinson-buck at ivanhoe.com.au>
f: +61 3 9490 3490
w: www.ivanhoe.com.au<http://www.ivanhoe.com.au/>
w: www.ivanhoe100.com.au<http://www.ivanhoe100.com.au/>
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