[Year 12 SofDev] DLTV Exam 1

[alan whittaker]

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
>  
> f: +61 3 9490 3490
> w: www.ivanhoe.com.au
> w: www.ivanhoe100.com.au
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