Arrays

Declaring a Array

• With subscript:– Dim numbers(2) as Integer– Using variable as subscript:

• Dim arrayIndex as Integer = 10• Dim myArray(arrayIndex) as Integer

• Without subscript– Dim numbers() as Integer = {2, 4, 6}– Dim someNames() as String = {“”, “”, “”}

• Note: Can not have a subscript with a initialization list. • Without subscript and initialization

– Dim numbers As Integer()– numbers = New Integer() {2, 4, 6}

Accessing Array Elements with a For … Next Loop

– Dim i As Integer = 0, sum As Integer = 0– For i = 0 To 2– sum += numbers(i)– Next

• GetUpperBound– For i = 0 to numbers.GetUpperBound(0)

sum += numbers(i)

– Next

• Length– For i = 0 to numbers.length-1

sum += numbers(i)

– Next

Accessing Array Elements with a For Each Loop

Dim i As Integer

For Each i In numbers

i = i * 2

MessageBox.Show(i.ToString)

Next

Array’s Properties and Methods• Properties:

– Length– IsFixedSize– IsReadOnly

• Methods– BinarySearch *** return negative value if not found– Clear– Clone, Copy, CopyTo– GetLowerBound, GetUpperBound– Reverse– Sort

Highest Values in a Array

Dim highest As Integer

highest = numbers(0)

For i = 1 To numbers.GetLowerBound(0)

If numbers(i) > highest Then

highest = numbers(i)

End If

Next

Searching ArraysDim found As Boolean = False

Dim searchValue As Integer

searchValue = InputBox("Enter search value: ")

For i = 0 To numbers.GetUpperBound(0)

If numbers(i) = searchValue Then

found = True

Exit For

End If

Next

If found Then

MsgBox("Number found")

Else

MsgBox("Number not found")

End If

Using Parallel Relationship between Array and Listbox

Private Sub Form4_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

ListBox1.Items.Add("Peter")

ListBox1.Items.Add("Paul")

ListBox1.Items.Add("Mary")

phone(0) = "1234"

phone(1) = "6789"

phone(2) = "3456"

End Sub

Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged

MessageBox.Show(ListBox1.SelectedItem & "phone is" & phone(ListBox1.SelectedIndex))

End Sub

ReDim

• ReDim numbers(5) – Original values in the array will be lost.

• ReDim Preserve numbers(5)• Use ReDim to assign size if the array is

declared without subscript.– Dim test As Integer()– …– ReDim test(2)

Passing Arrays as ArgumentsDim outstr As String

setnew(test)

For i = 0 To test.GetUpperBound(0)

outstr &= test(i).ToString & vbCrLf

Next

MessageBox.Show(outstr)

End Sub

Sub setnew(ByVal a() As Integer)

Dim i As Integer

For i = 0 To a.GetUpperBound(0)

a(i) = 0

Next

End Sub

Note: ByVal or ByRef? With ByVal, it will prevent an array argument from being assigned to another array.

Two-Dimensional Arrays

– Depts=1– Prods=2– Dim SalesData(Depts, Prods) As Double

• With initialization– Dim SalesData(,) as Double = {{20,30,15},{40,32,55}}

For Each Loops for 2-dimensional Array

Dim salesData(,) As Double = {{20, 15, 30}, {30, 21, 50}}

Dim totalSales, I As Double

For Each I In salesData

totalSales += I

Next

TextBox1.Text = totalSales.ToString

For Next Loops for 2-dimensional Array

Dim row, col As Integer

For row = 0 To salesData.GetUpperBound(0)

For col = 0 To salesData.GetUpperBound(1)

totalSales += salesData(row, col)

Next

Next

MessageBox.Show(totalSales.ToString)

Data Binding with Arrays

• Connect a control to one data source.

• Arrays can be used as data source for a control.

• Demo: ListBox DataSource property.– Dim fruits() As String = {"Apple", "Orange",

"Banana", "Strawberry", "Kiwi"}– ListBox1.DataSource = fruits

Collections

• Collections are used to store lists of objects.• More flexible than array:

– No need to declare the number of objects in a collection, no need to ReDim.

– Objects can be added, deleted at any position.– Object can be retrieved from a collection by a

key.

• A collection’s name usually end with a “s”.

Using Collections• Define a collection:

– Ex. Dim Pets as New Collection

• Methods:– ADD: Add object to a collection

• Pets.Add(“dog”)• Add an object with a key:

– Pets.Add(“Dog”, “D”)

– Item: Retrieve an object from a collection with a position index (base 1) or with a key.

• petName = Pets.Item(1)• petName = Pets.Item(“D”)

– Count: Return the number of objects in a collection.– Remove: Delete an object with a position index or key.

Iterating Through a CollectionDim Pets as New Collection

…

Dim Indx as Long

For Indx = 1 to Pets.Count

…operations …

Next Indx

For Each pet in Pets

… operations …

Next pet

Timer

• Event:– Tick

• Property:– Enable

– Interval property• measured in millisecond, 1000 millis = 1 second

• Methods:– Start

– Stop

Status Bar & Timer

• Status Bar– Panels property (collection)– Set ShowPanel property to true.– StatusBar1.ShowPanels = True

– StatusBarPanel1.Text = System.DateTime.Now.ToString

• Timer– Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal

e As System.EventArgs) Handles Timer1.Tick StatusBarPanel1.Text = System.DateTime.Now.ToString

End Sub

Bitmap Data Type

• To read a picture file to program:– Dim pic as New Bitmap(“c:\mypic.jpg”)

Rotate Form’s Background Image

Create a collection of pictures:

DIM PCOLAS NEW COLLECTION

Dim im1 As New Bitmap("c:\Paradise.jpg") Dim im2 As New Bitmap("c:\Flyaway.jpg") Dim im3 As New Bitmap("c:\SnowTrees.jpg") pcol.Add(im1) pcol.Add(im2) pcol.Add(im3)

Use Timer to change image:

Me.BackgroundImage = pcol.Item(counter)

counter = (counter Mod 3) + 1

• Me.BackgroundImage = pcol.Item(counter)

• counter = (counter Mod 3) + 1

Other Collection Classes

• ArrayList

• HashTable

• SortedList

• Stack

• Queue