VB.Net Loops

1
VB.Net Loops
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Loop

• FOR index start TO end STEP step
• statements
• EXIT FOR
• NEXT index
• DO WHILE UNTIL condition
• statements
• EXIT DO
• LOOP

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Do While/Do Until
Private Sub Command1_Click() Dim counter As
Integer counter 0 Do While counter lt 5
Debug.Write(counter) counter counter
1 Loop Text1.Text counter End Sub Private Sub
Button2_Click() Dim counter As Integer counter
0 Do Until counter gt 5 Debug.Write(counter)
counter counter 1 Loop Text1.Text
counter End Sub
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Loop DemoFuture Value
Dim output As String "Year" vbTab
"FutureValue" vbCrLf Dim output2 As String
"Year" vbTab "FutureValue" vbCrLf Dim
amount, principal, iRate, year As Single Dim
yearIndex As Integer principal
CSng(TextBox1.Text) iRate CSng(TextBox2.Text) ye
ar CSng(TextBox3.Text) For yearIndex 1 To
CInt(year) amount principal (1 iRate)
yearIndex output output yearIndex
vbTab FormatCurrency(amount) vbCrLf
output2 output2 yearIndex vbTab
String.Format("0c", amount) vbCrLf
Next MessageBox.Show(output, "FutureValue",
MessageBoxButtons.OK) MessageBox.Show(output2,
"FutureValue", MessageBoxButtons.OK) Note Use
the Do While, Do Until loops.
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Formatting Numbers for Output

• FormatNumber, FormatCurrency, FormatPercent
• (NumericExpression ,Decimal points. ),
• FormatDateTime(DateExpression, date format)
• String.Format(formatSring, Arg0, Arg1,)
• Ex strString.Format(0,10 1,20, x, y)
• 0 represents the first number, 10 reserves 10
  spaces.
• StrString.Format(The 1st number is 0 the 2nd
  number is 1, x, y)
• StrString.Format(0,10C, amount)
• Format code C, N, P, E, etc.
• Special characters
• vbTab, vbCrLf

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Example Display characters entered in
textbox1one at a time

• Dim index As Integer
• index 0
• For index 0 To TextBox1.TextLength - 1
• MessageBox.Show(TextBox1.Text.Substring(index,
  1))
• Next
• Problem 1 How many a entered in textbox1?
• Problem 2 How many words entered in textbox1?

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List Box

• Useful properties
• Items The items in the listBox. It is a
  collection strcture. Items can be entered at the
  design time or entered with code.
• SelectionMode one or multi selection
• SelectedItem(s), SelectedIndex
• Methods
• Add
• Clear

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List Box Example
Private Sub Form1_Load(ByVal sender As Object,
ByVal e As System.EventArgs) Handles MyBase.Load
TextBox1.Clear() TextBox2.Clear()
ListBox1.Items.Clear()
ListBox1.Items.Add("Apple")
ListBox1.Items.Add("Orange")
ListBox1.Items.Add("Banana")
ListBox1.Items.Add("Strawberry")
TextBox2.Text ListBox1.Items.Count.ToString
End Sub Private Sub ListBox1_SelectedIndexCha
nged(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles ListBox1.SelectedIndexCh
anged TextBox1.Text ListBox1.SelectedIte
m End Sub
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Selected Items Value

• Demo
• Select interest rate from a list box.

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ListBox Multiple Selections
Note The SelectionMode property must set to
multi selection. extBox2.Text
ListBox1.SelectedItems.Count.ToString Dim allSel
As String Dim i As Integer For i 0 To
ListBox1.SelectedItems.Count - 1 allSel
allSel ListBox1.SelectedItems.Item(I) Or
allSel allSel ListBox1.SelectedItems(I) Next
Or use the For Each loop Dim item As
String For Each item In ListBox1.SelectedItems
allSel allSel item Next TextBox3.Text
allSel
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Collections

• Collections are used to store lists of objects.
• A collections name usually end with a s.
• Items
• SelectedItems

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List Items Collections

• Methods
• ADD ListBox1.Items.Add("Apple")
• Item Retrieve an object from Items
• ListBox1.Items.Item(Index)
• ListBox1.Items(Index)
• 0-based index
• Insert ListBox.Items.Insert(Index, item)
• Remove Delete an object with a position index or
  key.
• ListBox.Items.Remove(Item)
• ListBox.Items.RemoveAt(Index)
• Listbox1.Refresh()
• Clear ListBox.Items.Clear()
• Count Return the number of objects in a
  collection.

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Iterating Through a Collection
Dim msg As String "you select" Dim i
As Integer 0 For i 0 To
ListBox1.SelectedItems.Count - 1 msg
msg ListBox1.SelectedItems(i) Next
TextBox1.Text msg
Dim Msg2 As String "You select " Dim
sitem As String For Each sitem In
ListBox1.SelectedItems Msg2 Msg2
sitem Next TextBox2.Text Msg2
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Using ListBox to Display Output
ListBox1.Items.Clear() ListBox1.Items.Add("Year"
vbTab "FutureValue") For yearIndex 1 To
CInt(year) amount principal (1 iRate)
yearIndex ListBox1.Items.Add(yearIndex.ToS
tring vbTab FormatCurrency(amount)) Next
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ComboBox

• Allows the user to type text directly into the
  combo box.
• Use the Text property to get entered item
• ComboBox1.Text
• The index for an entered item is 1.
• SelectedItem may be different from the Text
  property.
• Search an item in the list ComboBox1.Items.IndexO
  f(search text)
• Found return the index of the search text.
• Not found return 1.
• How to add an entered item to the list?

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Structured Error Handling
Try result Val(TextBox1.Text) /
Val(TextBox2.Text) TextBox3.Text
result.ToString Catch except As
DivideByZeroException
MessageBox.Show(except.Message)
Catch except As Exception
MessageBox.Show(except.Message)
Finally MessageBox.Show("I get
exdecuted, no matter what") End Try
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Enumerations

• Provide a way to associate meaningful names with
  a sequence of constant values.
• Define an enumeration using an Enum statement in
  classes, modules, and structures.
• Private Enum seasonOfYear
• Spring 1
• Summer 2
• Fall 3
• Winter 4
• End Enum

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Enumerations

• Provide a way to associate meaningful names with
  a sequence of constant values.

Enum enumTest spring 1 summer
fall winter End Enum Dim etest
As enumTest Private Sub Form1_Load(ByVal sender
As System.Object, ByVal e As System.EventArgs)
Handles MyBase.Load etest enumTest.summer
TextBox1.Text Val(etest).ToString
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Dim i, j, wordCount As Integer Dim
trimedText As String trimedText
TextBox1.Text.Trim() wordCount 0
If trimedText.Length 0 Then
wordCount 0 Else For i 0
To trimedText.Length - 1 If
trimedText.Substring(i, 1) Chr(Keys.Space)
Then wordCount 1
For j i To trimedText.Length - 1
If Not trimedText.Substring(j,
1) " " Then i j
Exit For
End If Next
End If Next
wordCount 1 End If
MessageBox.Show(wordCount.ToString "words")