VB6 Language Reference

' Declare with explicit type
Dim name As String
Dim age As Integer
Dim price As Double
Dim isActive As Boolean
Dim birthDate As Date

' Declare and assign
Dim message As String
message = "Hello, World!"

' Multiple declarations
Dim x As Integer, y As Integer, z As Integer

' Module-level (accessible across all procedures)
Private counter As Integer
Public sharedValue As String

' Simple Sub
Private Sub ShowMessage()
    MsgBox "Hello!"
End Sub

' Sub with parameters
Private Sub Greet(name As String)
    lblGreeting.Caption = "Hello, " & name & "!"
End Sub

' Sub with ByRef parameter (modifies original)
Private Sub DoubleIt(ByRef value As Integer)
    value = value * 2
End Sub

' Sub with ByVal parameter (copy, original unchanged)
Private Sub ProcessCopy(ByVal value As Integer)
    value = value + 10  ' Only affects local copy
End Sub

' Simple Function
Private Function Add(a As Integer, b As Integer) As Integer
    Add = a + b
End Function

' Using the function
Dim result As Integer
result = Add(5, 3)  ' result = 8

' Function with optional parameter
Private Function FormatName(firstName As String, Optional lastName As String = "") As String
    If lastName = "" Then
        FormatName = firstName
    Else
        FormatName = firstName & " " & lastName
    End If
End Function

' Boolean function
Private Function IsEven(num As Integer) As Boolean
    IsEven = (num Mod 2 = 0)
End Function

' Button click
Private Sub cmdSubmit_Click()
    MsgBox "Form submitted!"
End Sub

' Form load (initialization)
Private Sub Form_Load()
    Me.Caption = "My Application"
    txtName.Text = ""
    cboOptions.AddItem "Option 1"
    cboOptions.AddItem "Option 2"
End Sub

' Text changed
Private Sub txtInput_Change()
    lblLength.Caption = "Length: " & Len(txtInput.Text)
End Sub

' Key press (with parameter)
Private Sub txtInput_KeyPress(KeyAscii As Integer)
    ' Only allow numbers
    If KeyAscii < 48 Or KeyAscii > 57 Then
        KeyAscii = 0  ' Cancel the key
    End If
End Sub

' Timer event
Private Sub Timer1_Timer()
    lblTime.Caption = Time
End Sub

' Mouse events
Private Sub Canvas1_MouseMove(X As Single, Y As Single)
    lblCoords.Caption = "X: " & X & ", Y: " & Y
End Sub

' Fixed-size array
Dim numbers(10) As Integer     ' 0 to 10 (11 elements)
Dim matrix(5, 5) As Double     ' 2D array

' Dynamic array
Dim items() As String
ReDim items(5)                 ' Resize to 6 elements
ReDim Preserve items(10)       ' Resize, keep values

' Array with specific bounds
Dim months(1 To 12) As String

' Initialize array
numbers(0) = 10
numbers(1) = 20

' Array functions
LBound(numbers)     ' Lower bound (usually 0)
UBound(numbers)     ' Upper bound
Erase numbers       ' Clear/reset array

' Array from string
Dim parts() As String
parts = Split("a,b,c", ",")    ' ["a", "b", "c"]

' Loop through array
For i = LBound(arr) To UBound(arr)
    Debug.Print arr(i)
Next i

' Basic error handling
On Error GoTo ErrorHandler

Dim result As Double
result = Val(txtInput.Text) / Val(txtDivisor.Text)
lblResult.Caption = result
Exit Sub

ErrorHandler:
    MsgBox "Error: " & Err.Description
    Resume Next  ' Continue with next line

' Inline error handling
On Error Resume Next
result = 10 / 0
If Err.Number  0 Then
    MsgBox "Cannot divide by zero"
    Err.Clear
End If
On Error GoTo 0  ' Disable error handling

' Error object properties
Err.Number       ' Error number
Err.Description  ' Error message
Err.Source       ' Source of error
Err.Clear        ' Clear the error

' Simple message
MsgBox "Hello World!"

' With title
MsgBox "Operation complete", vbInformation, "Success"

' With buttons and check result
Dim response As Integer
response = MsgBox("Save changes?", vbYesNoCancel + vbQuestion, "Confirm")

If response = vbYes Then
    ' Save
ElseIf response = vbNo Then
    ' Don't save
Else
    ' Cancel
End If

' Button constants
vbOKOnly        ' OK button only
vbOKCancel      ' OK and Cancel
vbYesNo         ' Yes and No
vbYesNoCancel   ' Yes, No, and Cancel
vbRetryCancel   ' Retry and Cancel

' Icon constants
vbCritical      ' Error icon
vbQuestion      ' Question mark
vbExclamation   ' Warning icon
vbInformation   ' Info icon

' Input box
Dim name As String
name = InputBox("Enter your name:", "Name Input", "Default")
If name  "" Then
    lblGreeting.Caption = "Hello, " & name
End If