Dynamic Arrays can resize the capability of the Array at runtime .when you are in a situation that you do not know exactly the number of elements to store in array while you making the program. In that situations we are using Dynamic Array .

Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button1.Click
Dim i As Integer
Dim scores() As Integer

ReDim scores(1)
scores(0) = 100
scores(1) = 200

For i = 0 To scores.Length - 1
MsgBox(scores(i))
Next

ReDim Preserve scores(2)

scores(2) = 300

For i = 0 To scores.Length - 1
MsgBox(scores(i))
Next
End Sub
End Class

When you execute this source code , the first loop shows first two values stored in the Array. Next loop shows the whole value stored in the Array.

Initial declaration

Dim scores() As Integer

Resizing

ReDim scores(1)

If you want to keep the existing items in the Array , you can use the keyword Preserve .

ReDim Preserve scores(2)

In this case the Array dynamically allocate one more String value and keep the existing values.