Using Looping Structures and Lists Chapter 4

For … Next Statements Repeat a specific number of times For intCounter = 1 To 5 –Statement block Next intCounter intCounter values are 0,[1, 2, 3, 4, 5], 6 intCounter = 0 intCounter = 6

For … Next Statements Repeat a specific number of times For intCounter = 5 To 1 Step -1 –Statement block Next intCounter intCounter values are 0,[5, 4, 3, 2, 1], 0

For … Next Statements Repeat a specific number of times Counter must be a numeric variable, usually integer. Startvalue, Endvalue, and Stepvalue are numeric, usually integer, can be constants or variables. Startvalue, Endvalue can be positive, negative or zero. Stepvalue can be positive or negative but not zero. Stepvalue defaults to 1 is omitted.

For … Next Example Write a For Next loop where the user inputs the names of 4 players on a bowling team and displays them on different lines in a multi-line text box called txtPlayers.

For … Next Example For intCounter = 1 To 4 –strName = strName & InputBox(“Type a name for player “ & intCounter) & vbCrLf Next intCounter txtPlayers.Text = strName

For … Next Example intNbrOnTeam = Val(InputBox(“How many people are on the team?”)) For intCounter = 1 To intNbrOnTeam –strName = strName & InputBox(“Type a name for player “ & intCounter) & vbCrLf Next intCounter txtPlayers.Text = strName

Debug Technique intNbrOnTeam = Val(InputBox(“How many people are on the team?”)) For intCounter = 1 To intNbrOnTeam –strName = strName & InputBox(“Type a name for player “ & intCounter) & vbCrLf –Debug.Writeline(intCounter) –Debug.Writeline(strName) Next intCounter txtPlayers.Text = strName

Create a List of Interest Rates sngBegRate = Val(InputBox(“What is the beginning interest rate?”)) sngEndRate = Val(InputBox(“What is the ending interest rate?”)) For sngRate = sngBegRate To sngEndRate Step.05 –strRates = strRates & format(sngRate,”Percent”) & vbCrLf Next sngCounter txtRates.Text = strRates

Endless Loops A loop which will never reach the end value is an endless, or infinite, loop. This is the worst error you can make in coding. Changing the Counter value inside the loop can produce an endless loop. To exit an endless loop, press the ctrl and break keys together.

Incrementing Variables intCounter = IntCounter + 1 intCounter += 1 Each takes the value of integer counter, adds one to it, and stores the result in integer counter.

Working with Lists Use a ComboBox when the user needs to type in their own selection, this creates a possibility of input errors. ListBox – when the user is limited to the specific choices listed, no possibility of input errors.

ListBox Properties Items – String Collection Editor Index – points to a particular item in the list, indexes begin with 0. SelectionMode –None – no items may be selected. –One – only one item may be selected at a time. –MultiSimple – more than one item may be selected. –MultiExtended – more than one item may be selected.

Items.Add method Adds items to the collection during run time. Used for ComboBoxes and ListBoxes. Listboxname.Items.Add value Lists are usually populated in the Form load procedure.

Adding items to a list at run time. Listboxname.Items.Add value Numeric values can be added in a loop For sngRate =.05 To.12 Step.01 –lstRates.Items.Add sngRate Next sngRate lstRates.SetSelected = (2, True)

ListBox.SetSelected method listBox.SetSelected (index, value) The index refers to which item is selected. The selected value is either true or false. lstRates.SetSelected = (2, True) Selects the third item in the list as the default.

Determine the selected item A listbox used the SelectedIndex property to determine which item is selected. This only works for single select list boxes.

Which rate is selected? Select Case lstRates.SelectedIndex Case 0 Case 1 Case 2 Case 3 End Select

Display Payments in a List Box lstRates.Clear‘first clear the list For intCtr = 1 To intTerm * 12 –lstPayments.Items.Add (“Payment #” & intCtr & vbTab & Format(Pmt(sngRate/12, intTerm * 12, -decPrincipal), “Currency”) Next

For…Each…Next Statement This statement allows us to work with each item in a collection. A collection is a group of individual objects treated as one unit. Items in a ComboBox or ListBox are one kind of collection. Other collections are in Chapter 8.

For…Each…Next Statement Executes the statements in the loop for each element in a collection. For Each element In collection –Statements Next [element] Element is an object variable which keeps track of each item in a collection.

For…Each…Next Statement For Each objControl In Controls –If TypeOf objControl IS TextBox Then objTextBox = objControl If objTextBox.Visible Then –objTextBox.Visible = False Else –objTextBox.Visible = True End If –End If Next objControl

List Folders on a Disk Drive Dim strLetter As String Dim folders() As DirectoryInfo lstDir.Items.Clear() strLetter = InputBox(“Enter a drive letter.”) Folders = New DirectoryInfo(strLetter & “:\”) Dim folder as DirectoryInfo For Each folder In folders –lstDir.Items.Add(folder.FullName) Next