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Last Updated 6-30-2010

Visual Basic Parallel Arrays

That was fun, but what would really be lots more fun would be to see the name of the person associated with the score. That way, if their score is lower than ours, we can poke fun at them. But, we need to stay clear of that clown with the highest score.

Example 5

This time design a Visual Basic.NET program to display the name as well as the score. In a manner similar to the example above:

• This time associate the name of the student with their score.
• Enter scores between 0 and 100.
• Display the min and max values with the student's name
• So we can see who to make fun of, and who to avoid.

The following diagram illustrates 1 possibility of the form at design time:

Figure Array-11: Example 5 Form at Design Time

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The following diagram is the same form with the controls desginated by their name property:

Figure Array-12: Example 5 Form at Design Time Expanded

With the form designed, and all the controls given their name properties, enter the following code in the VB.Form tab:

Public Class Form1

'Declare Array Visible to Entire Class

Private NumberOfScores As Integer = 0
Private MaxEntries As Integer = 20
Private ScoreArray(MaxEntries ) As Double 
Private NameArray(MaxEntries ) As String 

'Enter Student Name - press <Enter> to place value into Array

Private Sub txtStudentName_Enter (ByVal sender As System .Object , _
        ByVal e As KeyEventArgs) Handles txtStudentName .KeyDown 

        Dim NameEntered As String 

        If e.KeyCode = keys.Enter then

            NameEntered = txtStudentName .Text 
            If NameEntered = "" then
                MessageBox .Show ("You must enter a Name")
                txtStudentName .Focus 
                Exit Sub 
            End If
            NameArray (NumberOfScores)=NameEntered 
            txtMidtermScore.Clear 
            txtMidtermScore.Focus 
        End If

End Sub 


'Enter scores - press  to place value into Array

Private sub   txtQuizScore_Enter (ByVal sender As System .Object , _
        ByVal e As KeyPressEventArgs ) Handles txtMidtermScore.KeyPress

    
    Dim EnteredValue As Double 
    Dim DataString As String 

    If e.KeyChar = ControlChars.Cr  Then
    
        If Double .TryParse (txtMidtermScore .Text ,EnteredValue  ) = False then
            MessageBox .Show (" You must enter a numeric value like 1 or 2")
            txtMidtermScore .Clear 
            txtMidtermScore .Focus 
            Exit Sub 
        End If

        If EnteredValue  < 0 or EnteredValue  >100 then
            MessageBox .Show ("Valid range is between 0 and 100, 7 would work " _
                & EnteredValue .ToString  & " Does not")
            txtMidtermScore .Clear 
            txtMidtermScore .Focus
            Exit Sub  
        End If

        If NumberOfScores < MaxEntries then
            ScoreArray (NumberOfScores) = EnteredValue 
          
            DataString = (NumberOfScores+1) .ToString + ".  " + _
                NameArray (NumberOfScores).PadRight (15) + _
			EnteredValue  .ToString.PadLeft (5) 
            lstDisplay.Items.Add (DataString )
            NumberOfScores += 1
        End If
        txtMidtermScore .Clear 
        txtStudentName .Clear 
        txtStudentName  .Focus 
        Exit Sub 
    End If 

' Handles user entering a <TAB> key

    If NameArray (NumberOfScores) = "" then
        If txtStudentName.Text <> "" then
            NameArray (NumberOfScores) = txtStudentName .Text 

        Else
            MessageBox.Show ("you must enter the name first")
            txtMidtermScore .Clear 
            txtStudentName .Clear 
            txtStudentName .Focus 
        End If
    End If

End Sub 

'Clear Last Entry

Private Sub btnClearLast_Click( ByVal sender As System.Object,  _
	ByVal e As System.EventArgs) Handles btnClearLast.Click
    NumberOfScores -= 1
    lstDisplay .Items .RemoveAt (NumberOfScores )
    txtMidtermScore .Clear 
    txtStudentName  .Clear 
    txtStudentName  .Focus 
    
End Sub

'Clear All Entries

Private Sub btnClearAll_Click( ByVal sender As System.Object,  _
	ByVal e As System.EventArgs) Handles btnClearAll.Click
    lstDisplay .Items .Clear 
    NumberOfScores = 0
    txtMidtermScore .Clear 
    txtStudentName  .Clear 
    txtStudentName .Focus 
End Sub

'Calculate Min, Max and Average

Private Sub btnStatistics_Click( ByVal sender As System.Object,  _
	ByVal e As System.EventArgs) Handles btnStatistics.Click
    Dim Output As String 
    Dim Average As Double = 0
    Dim Sum As Double = 0
    Dim ScoreNumber As Integer 
    Dim MinScore As Double = ScoreArray (0)
    Dim MaxScore As Double = ScoreArray (0)

    lstDisplay .Items .Add ("")

    For ScoreNumber =0 to NumberOfScores - 1
        Sum+=ScoreArray (ScoreNumber)
        If(MinScore > ScoreArray (ScoreNumber) ) then
            MinScore = ScoreArray (ScoreNumber)
        End If
        If(MaxScore < ScoreArray (ScoreNumber)) then
            MaxScore = ScoreArray (ScoreNumber)
        End If
    Next


    If(NumberOfScores>0 ) then
        Average = Sum/NumberOfScores
    End If
    

    Output ="Average: " + Average .ToString(".0")

    lstDisplay .Items .Add (Output )
    Output ="Minimum: " + MinScore .ToString 
    lstDisplay .Items .Add (Output )
    Output ="Maximum: " + MaxScore .ToString 
    lstDisplay .Items .Add (Output )

    txtMidtermScore .Clear 
    txtStudentName .Clear 
    txtStudentName .Focus 
    
    
End Sub

'Set the focus to the Student Name at Run Time

Private Sub Form1_Load( ByVal sender As System.Object,  ByVal e As System.EventArgs) _
    Handles MyBase.Load
    
    Dim MessageString As String 
    
    Me.ActiveControl=txtStudentName 

    MessageString = "First, Enter the student Name and Press , " +vbCrLf 
    MessageString += "then enter the student score and Press " +vbCrLf
    MessageString += "The Name and Score will be displayed in the Score Display"

    MessageBox.Show (MessageString)

    
End Sub
End Class
						

There are a couple of new concepts introduced in this code section:

• Private NumberOfScores As Integer = 0: Initialize the array index to 0
• Private MaxEntries As Integer = 20: This will be the maximum size of the array.
• Larger arrays will be declared dynamically, since this is just an example - fixed size is okay.
• Private ScoreArray(MaxEntries ) As Double: This is the array containing the numeric data of students course scores.
• Private NameArray(MaxEntries ) As String: This is the parallel array containing the names of the students in the course.


• Student name uses KeyEventArgs while Midterm Score optionally uses KeyEventPressArgs.


• Private Sub txtStudentName_Enter (ByVal sender As System .Object , ByVal e As KeyEventArgs) Handles txtStudentName .KeyDown
• Private Sub txtStudentName_Enter: This is the routine that is called every time a key is pressed in the student name TextBox, txtStudentName, each time checking for the <Enter> key to be pressed.
• ByVal sender as System.Object: Sender is Visual Basic's reference to the TextBox control.
• ByVal e as KeyEventArgs: e is the key information occuring every time a key is detected in the down position.
• Handles txtStudentName.KeyDown: This is the routine to be called when Windows detects a Key in the txtStudentName control.


• Private sub txtMidtermScore_Enter (ByVal sender As System.Object, ByVal e As KeyPressEventArgs) Handles txtMidtermScore.KeyPress
• Private sub txtMidTermScore_Enter: This function will be called when the <Enter> key is pressed in the TextBox.
• ByVal sender As System.Object: A reference to the TextBox control.
• ByVal e As KeyPressEventArgs e is every key pressed. KeyPressEventArgs decodes which key is pressed.
• Handles txtMidTermScore.KeyPress: Call this subroutine after every key press in the MidtermScoreTextBox.


• Dim EnteredValue As Double: This will be the numeric variable which receives the number entered in the textbox.
• Dim DataString as String: A String used to build a reflection of the data entered to be displayed in the ListBox.


• If e.KeyChar = ControlChars.Cr Then: Test for <Enter> key.
• e.KeyChar: The last key pressed in the TextBox.
• e: is the key pressed on the keyboard.
• KeyChar: is used as the reference in the KeyPressEventArgs class descriptor.
• ControlChars.Cr The comparison value for the <Enter> key when using KeyPressEventArgs.
• ControlChars: is used to decode KeyChar.
• Cr: is the value associated with the <Enter> key.


• If Double .TryParse (txtQuizScore .Text ,EnteredValue ) = False then: Check for Numeric Value.
• Double.TryParseSearch the text for a value of type double.
• txtMidtermScore.Text: The text is the Quiz Score TextBox is what will be scanned for a numeric value.
• EnteredValue: The recipient of the Double value if the scan is successful.
• =False then: Text was in improper format - execute code on next line.
• MessageBox .Show (" You must enter a numeric value like 1 or 2"): Display a message box gently guiding the user to the correct response.
• txtMidterm .Clear: Remove the information that was previously in the TextBox.
• txtMidtermScore.Focus: Place the Cursor in the empty TextBox, so they start right in entering data.
• Exit Sub: Error in Data Entry, no point in going any further.
• End If: End of Data Entry check for non-numeric value.


• If EnteredValue < 0 or EnteredValue >10 then: Check for valid range between 0 and 10.
• If NumberOfScores < MaxEntries then: Make sure they aren't getting too ambitious, and going out of bounds on the array.
• ScoreArray (NumberOfScores) = EnteredValue: All is good, place value in next array location.
• DataString = (NumberOfScores+1).ToString + ". "+NameArray(NumberOfScores).PadRight(15)+EnteredValue.ToString.PadLeft(5):
  • DataString=(NumberOfScores+1).ToString+". ": Enumerate the entry.
  • +NameArray(NumberOfScores).PadRight(15): Make Name be 15 spaces with blank spaces to the right.
  • +EnteredValue.ToString.PadLeft(5): Create string echoing number entered but 5 spaces wide.
• lstDisplay.Items.Add (DataString ): Visual Basic syntax to place data at the end of the ListBox display.
• NumberOfScores+=1 Move to Next array location.
• txtMidtermScore.Clear: Clear the Midterm Score TextBox.
• txtStudentName .Clear: Clear the Student Name TextBox.
• txtStudentName .Focus: Set the cursor in the Student Name TextBox.
• Exit Sub: It is important to not do the following Tab Check.



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• This section checks for a <TAB> key which is handled differently by Visual Basic


• If NameArray (NumberOfScores) = "" then: Check to see if the student name was processed.
• If txtStudentName.Text <> "" then: If the student name textbox is not empty - tab was pressed.
• NameArray (NumberOfScores) = txtStudentName .Text: Save the contents of the textbox into the array of names.


• Else: You are here if the name TextBox was left empty.


• MessageBox.Show ("you must enter the name first"): Instruct the user
• txtMidtermScore .Clear: Clear what was in the score.
• txtStudentName .Clear: Clear anything that was in the student name.
• txtStudentName .Focus: Place the cursor back in the student name TextBox



• This SUB clears the last entry out of the ListBox.


• Private Sub btnClearLast_Click( ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClearLast.Click.
• Visual Basic generated code to respond to the Clear Last Entry button being pressed.


• NumberOfScores -= 1: Reset Array index to last entry entered.
• lstDisplay .Items .RemoveAt (NumberOfScores ): Remove the Last Entry.
• txtMidtermScore.Clear: Clear the Midterm score textbox.
• txtStudentName.Clear: Clear the Student name textbox.
• txtStudentName.Focus: Place the cursor in the student name textbox.



• This Clears All Display Controls and sets the Focus on the Student Name.


• Private Sub btnClearAll_Click( ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClearAll.Click.
• Visual Basic Generated code to respond to the Clear All button being pressed.


• lstDisplay .Items .Clear: Syntax to clear a ListBox.
• NumberOfScores=0: Effectively clear the array by resetting the index to 0.
• txtMidtermScore.Clear: Clear the data entry TextBox.
• txtStudentName.Clear: Clear student name text box.
• txtStudentName.Focus: Set the cursor in the Student Name TextBox.




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• This Sub calculates Minimum, Maximum and Average Midterm Scores


• Private Sub btnStatistics_Click( ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnStatistics.Click.
• Visual Basic generated code to respond to the Statistics button being pressed.
• Dim Output As String: Workhorse variable to prepare text to send out to ListBox display.
• Dim Average As Double = 0: Preset the Average variable to 0 for clarity.
• Dim Sum As Double = 0: The sum must start at 0, in order for the average calculation to work.
• Dim ScoreNumber as Integer: Variable used to index through the Scores array.
• Dim MinScore As Double = ScoreArray (0): Set the minimum value to the first value in the array.
• Dim MinScore As Double = ScoreArray (0): Set the maximum value to the first value in the array.
• lstDisplay .Items .Add (""): Add in a blank line in the ListBox display.
• For ScoreNumber =0 to NumberOfScores - 1: Create For Loop to index through all Quiz Scores entered.
• Sum+=ScoreArray (ScoreNumber): Sum each score in the array.
• If(MinScore >ScoreArray (ScoreNumber) ) then: Check if the present score is lower than the previous minimum value.
• MinScore = ScoreArray (ScoreNumber): Set New Minimum if lower.
• If(MaxScore < ScoreArray (ScoreNumber)) then: Check if the present score is higher than the previous maximum value.
• MaxScore = ScoreArray (ScoreNumber): Set the New Maximum if higher.
• If(NumberOfScores>0 ) then: Check to make sure we don't get a /0 error.
• Average = Sum/NumberOfScores: Calculate the average.
• Output ="Average: " + Average .ToString: Create text to output Average.
• lstDisplay .Items .Add (Output ): Display the Average.
• Output ="Minimum: " + MinScore .ToString: Create and Display Minimum value.
• Output ="Maximum: " + MaxScore .ToString: Create and Display Maximum value.



• The FormLoad sub is used to set the focus on the student's name at Run Time


• Private Sub Form1_Load( ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
• Me.ActiveControl=txtStudentName: Set the focus on a control when the form loads in Visual Basic .NET
• Me: refers to the active form
• ActiveControl: The control which gets the focus and becomes active.
• txtStudentName The textbox where the student name is entered.

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