Adding an element to the end of an array

I would like to add a value to the end of a VBA array. How can I do this? I was not able to find a simple example online. Here's some pseudocode showing what I would like to be able to do.

Public Function toArray(range As range)
 Dim arr() As Variant
 For Each a In range.Cells
  'how to add dynamically the value to end and increase the array?
   arr(arr.count) = a.Value 'pseudo code
 Next
toArray= Join(arr, ",")
End Function

I solved the issue by using a Collection and copy it afterwards to an array.

Dim col As New Collection
For Each a In range.Cells
   col.Add a.Value  '  dynamically add value to the end
Next
Dim arr() As Variant
arr = toArray(col) 'convert collection to an array

Function toArray(col As Collection)
  Dim arr() As Variant
  ReDim arr(0 To col.Count-1) As Variant
  For i = 1 To col.Count
      arr(i-1) = col(i)
  Next
  toArray = arr
End Function

Try this [EDITED]:

Dim arr() As Variant ' let brackets empty, not Dim arr(1) As Variant !

For Each a In range.Cells
    ' change / adjust the size of array 
    ReDim Preserve arr(1 To UBound(arr) + 1) As Variant

    ' add value on the end of the array
    arr (UBound(arr)) = a.value
Next