Arrays of unknown length in Visual Basic

I have a piece of code written in Visual Basic:

Dim n As Double, i As Integer
n = 4
Dim Ramp_length(1 To 4) As Double
For i = 1 To n
    Ramp_length(i) = Cells(13 + i, 5)
    'Cells(65 + i, 7) = Ramp_length(i)'
Next i

Is there a way I can reproduce the result without declaring the array with a "fixed" length? I eventually want the code to read off a column of data with unknown length and store it in an array of equal or smaller length so it can be altered. This is just a piece of the code...if someone could help me out that woul开发者_如何学Pythond be great! :D

Thanks

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You can use ReDim Preserve to resize an array. If you only need it a view times and don't use it in a loop, it's ok. But ReDim Preserve is very slow, because it creates a completely new array and copies the old values into it. If you need to fill an array up with an unknown amount of data sets, use a list. I made a small example:

Dim num_iterations as Integer

' redim solution
Dim dyn_array As Integer()
For i = 0 To num_iterations - 1
    ReDim Preserve dyn_array(i)
    dyn_array(i) = i
Next

' list solution
Dim list_for_array As New List(Of Integer)
For i = 0 To num_iterations - 1
    list_for_array.Add(i)
Next
Dim list_array As Integer() = list_for_array.ToArray

With 10000 iterations the ReDim-solution has a runtime of 32ms, the list solution is instantly ready (0 ms). 100000 iterations result in 5487ms using ReDim and 1ms using a list.

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Not sure if this is what you're looking for:

    Dim n As Double = 44
    Dim Ramp_Length_List As New List(Of Double)
    For i As Integer = 1 To n
        Ramp_Length_List.Add(Your_Temp_Double)
    Next i

    Dim Ramp_Length(Ramp_Length_List.Count - 1) As Double
    For i As Integer = 0 To Ramp_Length_List.Count - 1
        Ramp_Length(i) = Ramp_Length_List(i)
    Next
    Ramp_Length_List = Nothing
    'Ramp_Length() as Double is now sort of dynamic.

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Dim DynaStrings() As String
ReDim DynaStrings(10)
DynaStrings(0) = "String 0"
'Need more data space!
ReDim DynaStrings(100)
DynaStrings(50) = "String 50"

Hope this might help.

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There's no such a thing, array with "dynamic" length.

You can, however, encapsulate some logic that will resize the array whenever needed (this is known as ResizeArray in some languages, List in others, or ArrayList; I'm sorry, I don't know exactly which one in VB; if it's VB.NET then use "List").

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You could use an ArrayList. It's the closest you can come to a dynamic array. There are other collections as well, so it may come down to what you expect to do with the data. However, you can't create an array and vary it's length dynamically in vb. (Well, not efficiently :) )