Using ReDim to initialize an array.

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I posted this on the msdn forums, but I didn't get an answer that directly relates to my question. So I'm reposting it here for you 9ers.

 

I'm currently reading "Data Structures and Algorithms using VB.Net" and in one the author's examples, he initializes an array of integers using ReDim Preserve. I was a bit confused as to why he would do that, since the array is empty. So I ran a test

initializing an array using ReDim Preserve against arry = new Integer(number){} and the ReDim Preserve was faster.

 

Here is part of the code:

 

Module Module1

 

*** Sub Main()

******* Dim arry As New CArray(9)

 

******* Dim sw = New Stopwatch()

******* sw.Start()

******* For index = 0 To 49

*********** arry.Insert(index)

******* Next

******* sw.Stop()

******* arry.showArray()

******* Console.WriteLine(sw.Elapsed)

******* Console.ReadLine()

 

*** End Sub ' Main

 

*Class CArray

 

******* Private arr() As Integer

******* Private numElements As Integer

 

******* Public Sub New(ByVal number As Integer)

 

*********** ReDim Preserve arr(number) ' faster

*********** 'arr = New Integer(number) {} ' slower

*********** 'ReDim arr(number) ' about the same as* 2nd example

*********** numElements = 0

 

******* End Sub

...

 

The ReDim Preserve averaged out at .00058 while

arry = new Integer(number){} averaged at about .0027

 

Ok, now why did the author use ReDim Preserve when the array hasn't been intialized with anything yet?

Is it because he knew that it was faster?

 

Um, they don't teach us to declare arrays like that in school or in our textbooks thats why I was confused when I saw that.

Any ideas?

 

Thanks.

 

 

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