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 Arrays Dim 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 Arguments Dim 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 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 Collection Dim 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