Programming 2 */ Arrays */

Arrays are programming constructs that store data and allow us to access them by numeric index or subscript. Arrays helps us create shorter and simpler code in many situations. Arraysin Visual Basic .NET inherit from the Array class in the System namespace. All arrays in VB are zero based, meaning, the index of the first element is zero and they are numbered sequentially. You must specify the number of array elements by indicating the upper bound of the array. The upper bound is the numder that specifies the index of the last element of the array. Arrays are declared using Dim, ReDim, Static, Private, Public and Protected keywords. An array can have one dimension (liinear arrays) or more than one (multidimensionalarrays). The dimensionality of an array refers to the number of subscripts used to identify an individual element. In Visual Basic we can specify up to 32 dimensions. Arrays do not have fixed size in Visual Basic.

The following code demonstrates arrays.

Imports System.Console
Module Module1
Sub Main()
Dim sport(5) As String
'declaring an array
sport(0) = "Soccer"
sport(1) = "Cricket"
sport(2) = "Rugby"
sport(3) = "Aussie Rules"
sport(4) = "BasketBall"
sport(5) = "Hockey"
'storing values in the array
WriteLine("Name of the Sport in the third location" & " " & sport(2))
'displaying value from array
End Sub
End Module

You can also declare an array without specifying the number of elements on one line, you must provide values for each element when initializing the array. The following lines demonstrate that:

Dim Test() as Integer
'declaring a Test array
Test=New Integer(){1,3,5,7,9,}

Reinitializing Arrays

We can change the size of an array after creating them. The statement assigns a completely new array object to the specified array variable. You use ReDim statement to change the number of elements in an array. The following lines of code demonstrate that. This code reinitializes the Test array declared above.

Dim Test(10) as Integer
ReDim Test(25) as Integer
'Reinitializing the array

When using the Redim statement all the data contained in the array is lost. If you want to preserve existing data when reinitializing an array then you should use the Preserve keyword which looks like this:

Dim Test() as Integer={1,3,5}
'declares an array an initializes it with three members
ReDim Preserve Test(25)
'resizes the array and retains the the data in elements 0 to 2

HashTable stores a Key Value pair type collection of data . We can retrive items from hashTable to provide the key . Both key and value are Objects.

Public Class Form1
    Private Sub Button1_Click(ByVal sender As System.Object, 
 ByVal e As System.EventArgs) Handles Button1.Click
        Dim weeks As New Hashtable
        Dim day As DictionaryEntry
        weeks.Add("1", "Sun")
        weeks.Add("2", "Mon")
        weeks.Add("3", "Tue")
        weeks.Add("4", "Wed")
        weeks.Add("5", "Thu")
        weeks.Add("6", "Fri")
        weeks.Add("7", "Sat")
        'Display a single Item
        MsgBox(weeks.Item("5"))
        'Search an Item
        If weeks.ContainsValue("Tue") Then
            MsgBox("Find")
        Else
            MsgBox("Not find")
        End If
        'remove an Item
        weeks.Remove("3")
        'Display all key value pairs
        For Each day In weeks
            MsgBox(day.Key  "  --  "  day.Value)
        Next
    End Sub
End Class

The Queue is another adtastructure from VB.NET Collections. Queue works like First In First Out method and the item added first in the Queue is first get out from Queue. We can Enqueue (add) items in Queue and we can Dequeue (remove from Queue ) or we can Peek (that is get the reference of first item added in Queue ) the item from Queue.

Public Class Form1
    Private Sub Button1_Click(ByVal sender As System.Object,_
 ByVal e As System.EventArgs) Handles Button1.Click
        Dim queueList As New Queue
        queueList.Enqueue("Sun")
        queueList.Enqueue("Mon")
        queueList.Enqueue("Tue")
        queueList.Enqueue("Wed")
        queueList.Enqueue("Thu")
        queueList.Enqueue("fri")
        queueList.Enqueue("Sat")
        MsgBox(queueList.Dequeue())
        MsgBox(queueList.Peek())
        If queueList.Contains("Sun") Then
            MsgBox("Contains Sun ")
        Else
            MsgBox("Not Contains Sun ")
        End If
    End Sub
End Class