Lesson 9: Mastering Variables and Constants in VB2022

' Basic variable declaration
Dim userName As String

' Declaration with initialization
Dim itemCount As Integer = 0

' Multiple declarations
Dim x, y, z As Integer
Dim firstName As String, age As Integer, isStudent As Boolean

' Valid variable names
Dim customerName As String
Dim total_amount As Decimal
Dim _tempValue As Integer

' Invalid variable names
' Dim 2023Total As Integer  ' Starts with number
' Dim user name As String   ' Contains space
' Dim Dim As Integer        ' Reserved keyword

' Module-level variable
Private moduleCounter As Integer = 0

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    ' Procedure-level variable
    Dim clickMessage As String = "Button clicked"
    
    ' Static variable retains value between calls
    Static clickCount As Integer = 0
    clickCount += 1
    moduleCounter += 1
    
    ' Block-level variable
    If clickCount > 5 Then
        Dim warning As String = "Too many clicks!"
        MessageBox.Show(warning)
    End If
    
    Label1.Text = $"{clickMessage} {clickCount} times (Total: {moduleCounter})"
End Sub

Private Sub BtnCalculate_Click(sender As Object, e As EventArgs) Handles BtnCalculate.Click
    ' Declare variables
    Dim num1 As Double = Double.Parse(TxtNum1.Text)
    Dim num2 As Double = Double.Parse(TxtNum2.Text)
    Dim result As Double
    
    ' Perform calculation based on operator
    Select Case CmbOperator.SelectedItem.ToString()
        Case "+"
            result = num1 + num2
        Case "-"
            result = num1 - num2
        Case "*"
            result = num1 * num2
        Case "/"
            If num2 <> 0 Then
                result = num1 / num2
            Else
                MessageBox.Show("Cannot divide by zero!")
                Exit Sub
            End If
    End Select
    
    ' Display result
    LblResult.Text = $"{num1} {CmbOperator.SelectedItem} {num2} = {result}"
End Sub