Structure Example Part II

Sub Validate to ensure proper Entry format by the user on the form.

First Validate the Last Name Text Box.

Private Sub ValidateData(): No parameters need to be sent since we declared all of our variables as 'Global'.
Dim LastName As String: Container for the data entered in the TextBox txtLastName.
LastName = txtLastName.Text: Transfer the text in the TextBox txtLastName to variable LastName.
If LastName = "" Then: The only requirements for a valid entry is that it not be empty.
MessageBox.Show("Please Enter the Student's Last Name"): Something to tell the user they made a mistake.
txtLastName.Clear(): Whatever they put in was wrong, so get rid of it.
txtLastName.Focus(): Put the cursor in the right location - just in case they cant' figure it out on their own.
Exit Sub: No point in checking any further - this must be resolved first.

Second Validate the First Name Text Box.

Dim FirstName As String: Container for the data entered in the TextBox txtFirstName.
FirstName = txtFirstName.Text: Transfer the text in the TextBox txtFirstName to variable FirstName.
If FirstName = "" Then: The entry must contain something.
MessageBox.Show("Please Enter the Student's First Name"): Inform user of corrective action.
txtFirstName.Clear(): Good practice to clear incorrect response.
txtFirstName.Focus(): Indicate where the correction needs to be made.
Exit Sub: Perform corrective action.

Third Validate Student ID

Dim StudentID As String: Create a container for the data entered in the TextBox txtStudentID.
Dim IDComponents() As String: Create a container for the 3 sections of the Student ID.
StudentID = txtStudentID.Text: Transfer the text in the TextBox txtStudentID to the variable StudentID.
IDComponents = StudentID.Split("-"): Split the student ID into the 3 sections separated by the '-'.
If IDComponents.Length <> 3: There should be 3 character sets returned from the Split.
IDComponents(0).Length <> 3: There are 3 characters in the first character set. i.e. '311'.
IDComponents(1).Length <> 2: There are 2 characters in the middle character set.
IDComponents(2).Length <> 4: There are 4 characters in the last character set.
IsNumeric(IDComponents(0)) = False: Each of the characters will be numeric if properly entered.
MessageBox.Show("Please enter ID in proper Format: ###-##-####"): Instruct proper format.
txtStudentID.Clear(): Get rid of the junk in there.
txtStudentID.Focus(): Place cursor at proper location.
Exit Sub: Let them try to fix their entry again.

Fourth - Validate the GPA Entry.

Dim strGPA As String: Create a Container for the data in the TextBox txtStudentGPA.
strGPA = txtStudentGPA.Text: Transfer the Text in TextBox txtStudentGPA to the variable strGPA.
If IsNumeric(strGPA) = False Then: The entry must be in Numeric format.

Dim dblGPA As Double: Create a container for the Numeric Value of the Text obtained from the user.
dblGPA = CDbl(strGPA): Convert the string to a Double.
If dblGPA < 0 Or dblGPA > 4 Then: Test for a proper range between 0 and 4.

ReDim Preserve Student(StudentIndex): If the data validates, increase the Array size by 1.
Transfer data from Variables into appropriate structure elements:

Student(StudentIndex).LastName = LastName
Student(StudentIndex).FirstName = FirstName
Student(StudentIndex).ID = StudentID
Student(StudentIndex).GPA = dblGPA

AddEntry(StudentIndex): Display entry in ListBox - optional at this point.
StudentIndex += 1: Get ready for next entry.

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The following event occurs when a user clicks on the ListBox.

Private Sub lstDisplay_SelectedIndexChanged: Generated Event by Visual Basic ListBox Click.
Dim Index As Integer: A variable to contain the location of the mouse-click.
Index = lstDisplay.SelectedIndex: Determine the entry corresponding to the Visual Basic ListBox Click.
DisplaySelectedStudent(Index): Display the student information that correspond to the user selection.

The following Sub transfers data from a structure element to the TextBoxes on the form:

Private Sub DisplaySelectedStudent(ByRef Index As Integer)
        txtFirstName.Text = Student(Index).FirstName
        txtLastName.Text = Student(Index).LastName
        txtStudentID.Text = Student(Index).ID
        txtStudentGPA.Text = Student(Index).GPA.ToString(".00")
End Sub

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The following Sub is Generated when the Exit Button is pressed:

Private Sub btnExit_Click(ByVal sender As System.Object, _
           ByVal e As System.EventArgs) Handles btnExit.Click
        Me.Close()
End Sub

The following Sub is Generated when the Calculate GPA button is pressed:

Private Sub btnAverageGPA_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAverageGPA.Click:
- Visual Basic Event-Driven Generated Sub when Calculate GPA Button is pressed.
Dim Index As Integer: Variable used to step through each Structure element in Student Array.
Dim Sum As Double: Variable Used to hold the Sum of every GPA in Student Array.
Dim Ave As Double: Variable used to hold the calculated GPA average.
For Index = 0 To StudentIndex - 1: Step through every Array Element.
Sum += Student(Index).GPA: Sum the GPAs and retain the result in Sum.
If StudentIndex > 0 Then: Avoid /0 error.
Ave = Sum / StudentIndex: Calculate Average.
txtAverageGPA.Text = "Class Ave = " + Ave.ToString(".00"): Display Calculated Average in TextBox txtAverageGPA.

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The following Sub is Generated when the Enter Button is pressed.

Private Sub btnEnter_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnEnter.Click:
- Visual Basic Event-Driven Generated Sub when Enter button is pressed.
ValidateData(): Validate Data - Update database if entered information is correct.
txtAverageGPA.Clear(): Calculated GPA is no longer valid - Clear the display.
ClearTextFields(): Clear all other fields to prepare for next entry.

The following button is pressed when the Search button is pressed:

Private Sub btnSearch_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSearch.Click
- Visual Basic Event-Driven Generated Sub when Search button is pressed.
Dim ID As String: Container for ID value user enters as search parameter.
Dim Index As Integer: Variable to step through each Array element.
Dim MatchFound As Boolean = False: Flag used to indicate whether or not a match was found.
ID = InputBox("Please Enter the Student's SSN (ID)", "Student Search": Use Input Box to Get User Search Parameter.

ID = InputBox: Place data from Visual Basic InputBox into variable ID.
"Please Enter the Student's SSN (ID)", "Student Search": Prompt given to user.
"Student Search": Title of Visual Basic InputBox.

If ID <> "" Then: Look for a match if they didn't cancel.
For Index = 0 To StudentIndex - 1: Step through every Array element.
If ID = Student(Index).ID Then: Test for Match.
DisplaySelectedStudent(Index): Place the matched data in the Visual Basic form TextBoxes.
MatchFound = True: Set Flag as successful match found.
Display notification if no matches were found:

If MatchFound = False Then
	MessageBox.Show("No Match Found for " + ID)
       ClearTextFields()
End If

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The following event is generated by pressing the Display Button:

Private Sub btnDisplay_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDisplay.Click:
- Visual Basic Event-Driven Generated Sub when Display button is pressed.
lstDisplay.Items.Clear(): Visual Basic statement to clear ListBox control.
Dim Index As Integer: Variable used to step through every Array element.
For Index = 0 To StudentIndex - 1: Step through every Array Structure Element.
AddEntry(Index): Place the corresponding entry in the Visual Basic ListBox lstDisplay.