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Last Updated 6-30-2010

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  • User Defined Data Types

    Visual Basic allows programmers to define a Visual Basic User Defined Data Type. A well-constructed User Defined Data Type can help make a program easier to understand and work with. One example of a Visual Basic User Define Data Type is the Structure construct. The Structure Data Type is composed of two or more standard data types. Some examples of Visual Basic standard data types are: Integer, Double, and String. So, some company like Jenny Craig can combine a string for the member's name and a double for their current weight. An example of how this might look coule be something like: Member.Name="Kirsty Allie" and Member.Weight=288.6. The structure construct gives a convenient way to group attributes (like name, weight and age) with a common object (like Member or pigeon or even MealTicket).

    Visual Basic Structure Declaration Syntax

    Syntax: Private/Public Structure StructureName

    • Private/Public:
      • Private: Example: Private Structure Employee. Private is used to limit scope to module.
      • Public: Example: Public Structure Student. Public is used to give scope to entire project.
    • Structure: Keyword Declaring Structure Construct.
    • StructureName: User supplied name to describe name of Structure Construct.
    • A structure may not be defined locally within a procedure or function - It must be public or private.

    Visual Basic Split Method Description

    The Visual Basic Split String method allows you to split a line of text and put each element (letter, word, or phrase) int an array:

    String Split Method - General Syntax:
    	Dim StringArray As String
    	StringArray = StringVariableName.Split ( delimiter character )
    Split Method Description:
    • Is a method of the string class.
    • It breaks up a string into substrings that are separated by a certain character, the delimiter character.
      • Typically a space, dash('-'), or forward slash ('/')
    • When the Split Method is invoked, an array of strings is returned.

    Figure UDDT-1: General Syntax for Split Method.

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    Visual Basic IsNumeric Data Validation Function

    The Visual Basic IsNumeric Data Validation Function is an intrinsic function in VB.NET that takes string data as an input argument, and checks it for being a numeric string. The functiion returns a Boolean output of true or false. Often, the IsNumeric function is used to check the data entered into a TextBox for being a numeric string. Typically, the IsNumeric function is used in conjunction with an If...then statement.

    IsNumeric Function - General Syntax:
    	IsNumeric ( string expression )
    IsNumeric Function Used for Data Validation:
    	Private Sub btnCalculate_Click(ByVal sender as System.Object, _
    		ByVal e As System.EventArgs) Handles btnCalculate.Click
    		If IsNumeric ( txtSubtotal.Text ) = false Then
    			MessageBox.Show("Please enter a valid Number")
    			Exit Sub
    		End If
    		' Code if Data was entered properly
    	End Sub
    IsNumeric Function - Description
    • Data Validation: The process of verifying that all user entries are valid.
      • One goal of this verification is to prevent runtime errors.
    • The IsNumeric function tests whether the value of an expression is numeric.
      • The function returns a Boolean value, which can be tested in a conditional expression.
      • If the Boolean value is true, the expression is numeric.
    • The IsNumeric function treats both positive and negative numbers as valid.
    • The IsNumeric function treats both numbers with and without decimal places as valid.

    Figure UDDT-2: General Syntax and Example for IsNumeric Function

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    Armed with all this knowledge, it looks like we are ready to tackle the next challenge:

    Design a VisualBasic.NET project to store the following data about students in a class. The data includes the student's last name, first name, student id, and GPA. Allow the user to enter the data for each student followed by a click on a Button so store the data in a dynamic array of structures. Add Buttons to display:

    1. Enter the student data.
    2. Display the student data in a listbox.
    3. Compute the class average GPA.
    4. End Program Execution.
    5. Perform a search based on the Student - ID.
      • Use an Input Box function to get the student's ID.

    Write a general function to validate the input data before processing. The validation rules are:

    1. Last Name must exist.
    2. First Name must exist.
    3. Student ID must be in the form: ###-##-####.
    4. the GPA must be a number between 0 and 4.

    Based on the preceding specifications, the following diagram is one possible configuration:

    Design Form

    Figure Structure-1: Student Data Form Design

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    Enter the following code into your Visual Basic Source Code (Form) Window:

    Public Class Form1
        Private Structure StudentRecord
            Dim LastName As String
            Dim FirstName As String
            Dim ID As String
            Dim GPA As Double
        End Structure
        Dim Student() As StudentRecord
        Dim StudentIndex As Integer
    	' AddEntry transfers the data in the TextBoxes on the Form
    	' To the Next Student Record Structure
        Private Sub AddEntry(ByVal Index As Integer)
            Dim DataString As String
            Dim FullName As String
            FullName = Student(Index).LastName + ", " + _
            DataString = FullName.PadRight(20) + _
                Student(Index).ID.PadRight(14) + _
        End Sub
    	'Sub to Validate proper Entry format on the form
        Private Sub ValidateData()
            Dim LastName As String
            LastName = txtLastName.Text
            If LastName = "" Then
                MessageBox.Show("Please Enter the Student's Last Name")
                Exit Sub
            End If
            Dim FirstName As String
            FirstName = txtFirstName.Text
            If FirstName = "" Then
                MessageBox.Show("Please Enter the Student's First Name")
                '            Me.ActiveControl = txtFirstName
                Exit Sub
            End If
            Dim StudentID As String
            Dim IDComponents() As String
            StudentID = txtStudentID.Text
            IDComponents = StudentID.Split("-")
            If IDComponents.Length <> 3 Or _
                IDComponents(0).Length <> 3 Or _
                IDComponents(1).Length <> 2 Or _
                IDComponents(2).Length <> 4 Or _
                IsNumeric(IDComponents(0)) = False Or _
                IsNumeric(IDComponents(1)) = False Or _
                IsNumeric(IDComponents(2)) = False Then
                MessageBox.Show("Please enter ID in proper Format: ###-##-####")
                Me.ActiveControl = txtStudentID
                Exit Sub
            End If
            Dim strGPA As String
            strGPA = txtStudentGPA.Text
            If IsNumeric(strGPA) = False Then
                MessageBox.Show("Please Enter a Grade Point Average Number between 0 and 4.0")
                Me.ActiveControl = txtStudentGPA
                Exit Sub
            End If
            Dim dblGPA As Double
            dblGPA = CDbl(strGPA)
            If dblGPA < 0 Or dblGPA > 4 Then
                MessageBox.Show("Please enter a Grade Point Average Number between 0 and 4.0")
                Me.ActiveControl = txtStudentGPA
                Exit Sub
            End If
            ReDim Preserve Student(StudentIndex)
            Student(StudentIndex).LastName = LastName
            Student(StudentIndex).FirstName = FirstName
            Student(StudentIndex).ID = StudentID
            Student(StudentIndex).GPA = dblGPA
            StudentIndex += 1
        End Sub
    	'Event Generated by Clicking on the ListBox
        Private Sub lstDisplay_SelectedIndexChanged(ByVal sender As System.Object, _
                ByVal e As System.EventArgs) Handles lstDisplay.SelectedIndexChanged
            Dim Index As Integer
            Index = lstDisplay.SelectedIndex
        End Sub
    	'Sub to transfer data from Structure element to Form TextBoxes
        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
    	' Event Generated when Clear Button Is pressed
        Private Sub txtLastName_Click(ByVal sender As System.Object, _
                ByVal e As System.EventArgs) Handles txtLastName.Click
        End Sub
    	'Sub to clear all TextBoxes at once.
        Private Sub ClearTextFields()
        End Sub
    	'Event Generated when Exit Button is pressed
        Private Sub btnExit_Click(ByVal sender As System.Object, _
                ByVal e As System.EventArgs) Handles btnExit.Click
        End Sub
    	'Event Generated by Pressing Calculate Class GPA Button
        Private Sub btnAverageGPA_Click(ByVal sender As System.Object, _
                ByVal e As System.EventArgs) Handles btnAverageGPA.Click
            Dim Index As Integer
            Dim Sum As Double
            Dim Ave As Double
            For Index = 0 To StudentIndex - 1
                Sum += Student(Index).GPA
            If StudentIndex > 0 Then
                Ave = Sum / StudentIndex
            End If
            txtAverageGPA.Text = "Class Ave = " + Ave.ToString(".00")
        End Sub
    	' Event Generated when Enter Button is pressed
        Private Sub btnEnter_Click(ByVal sender As System.Object, _
                ByVal e As System.EventArgs) Handles btnEnter.Click
        End Sub
    	' Event Generated when Search Button is pressed
        Private Sub btnSearch_Click(ByVal sender As System.Object, _
                ByVal e As System.EventArgs) Handles btnSearch.Click
            Dim ID As String
            Dim Index As Integer
            Dim MatchFound As Boolean = False
            ID = InputBox("Please Enter the Student's SSN (ID)", "Student Search")
            If ID <> "" Then
                For Index = 0 To StudentIndex - 1
                    If ID = Student(Index).ID Then
                        MatchFound = True
                    End If
            End If
            If MatchFound = False Then
                MessageBox.Show("No Match Found for " + ID)
            End If
        End Sub
    	' Event Generated by Pressing the Display Button
        Private Sub btnDisplay_Click(ByVal sender As System.Object, _
                ByVal e As System.EventArgs) Handles btnDisplay.Click
            Dim Index As Integer
            For Index = 0 To StudentIndex - 1
        End Sub
    End Class

    Figure Structure-2: Source Code for Example 1

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    The function of the code is outlined below. Program statements are in bold, Comments are in blue and explanations are in normal text:

    In order to continue with this guide, complete explanation of this example, and cover many other breathtaking examples, press the Press the Button below:

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    Visual Basic

    Introduction to VB.NET

    .NET Framework

    VS2008 IDE

    How VB is Compiled

    Start Visual Studio

    Windows Form App

    Save Your Work

    VB OOP Programming

    Visual Basic Code

    Exit Code

    Button Event Code

    Coding Recommendations


    Error List Window

    Comment Syntax

    Help Window

    Language Essentianl

    Built-In Data Types

    Declare Variables

    Declare Constants

    Code Arithmetic Expressions

    Assignment Statements

    Operator Precedence

    Type Casting

    Math Class

    String Declaration

    Conversion Functions

    Conversion Methods

    Formatting Functions

    String Formatting

    Variable Scope


    Nullable Types

    Loop Constructs

    For Next Loop

    Do While Loop

    Do Until Loop



    Exit Do | Exit For


    Nested Loops


    Array Declaration

    Rnd( ) Function

    Listbox Control


    Parallel Arrays

    Key Event Args

    Dynamic Arrays

    Redimension Array

    Set Breakpoint

    Start Debugger

    ReDim Preserve

    MultiDimensional Arrays

    DataGridView Control

    Length and Sort Methods


    Pad Right

    Split Method

    IsNumeric Function

    Multiform Projects

    Add Form To Project

    Form Object Methods

    Form Show Method

    ShowDialog Method

    Form Close Method

    Form Accept Button

    Multiform Project Example

    ASP.NET Web Programming

    Create Data Source

    Configure Access Data Source

    Add Product Class

    Extract Local Database Data

    Order PageLoad VB Code

    Add New Web Page

    Set Start Page

    Display Cart Aspx Code

    Display Cart Design View

    Sorted List Definition

    VB.NET Session State

    Create CartItem Class

    GetCartContents Function

    Add To Cart Event Handler

    Remove Cart Item Event

    Clear Cart Event Handler