You use declaration statements to name and define procedures, variables, properties, arrays, and constants. When you declare a programming element, you can also define its data type, access level, and scope. For more information, see Declared Element Characteristics.

The following example contains three declarations.

Public Sub applyFormat()
    Const limit As Integer = 33
    Dim thisWidget As New widget
    ' Insert code to implement the procedure.
End Sub

The first declaration is the Sub statement. Together with its matching End Sub statement, it declares a procedure named applyFormat. It also specifies that applyFormat is Public, which means that any code that can refer to it can call it.

The second declaration is the Const statement, which declares the constant limit, specifying the Integer data type and a value of 33.

The third declaration is the Dim statement, which declares the variable thisWidget. The data type is a specific object, namely an object created from the Widget class. You can declare a variable to be of any elementary data type or of any object type that is exposed in the application you are using.

Initial Values

Dim m As Integer = 45
' The preceding declaration creates m and assigns the value 45 to it.

Dim f As New System.Windows.Forms.Form()

An executable statement performs an action. It can call a procedure, branch to another place in the code, loop through several statements, or evaluate an expression. An assignment statement is a special case of an executable statement.

The following example uses an If...Then...Else control structure to run different blocks of code based on the value of a variable. Within each block of code, a For...Next loop runs a specified number of times.

Public Sub startWidget(ByVal aWidget As widget, 
    ByVal clockwise As Boolean, ByVal revolutions As Integer)
    Dim counter As Integer
    If clockwise = True Then
        For counter = 1 To revolutions
            aWidget.spinClockwise()
        Next counter
    Else
        For counter = 1 To revolutions
            aWidget.spinCounterClockwise()
        Next counter
    End If
End Sub

The If statement in the preceding example checks the value of the parameter clockwise. If the value is True, it calls the spinClockwise method of aWidget. If the value is False, it calls the spinCounterClockwise method of aWidget. The If...Then...Else control structure ends with End If.

The For...Next loop within each block calls the appropriate method a number of times equal to the value of the revolutions parameter.

Assignment statements carry out assignment operations, which consist of taking the value on the right side of the assignment operator (=) and storing it in the element on the left, as in the following example.

v = 42

In the preceding example, the assignment statement stores the literal value 42 in the variable v.

Eligible Programming Elements

x = y + z + findResult(3)

Data Types in Assignment Statements

Dim a, b As String
a = "String variable assignment"
b = "Con" & "cat" & "enation"
' The preceding statement assigns the value "Concatenation" to b.

Dim r, s, t As Boolean
r = True
s = 45 > 1003
t = 45 > 1003 Or 45 > 17
' The preceding statements assign False to s and True to t.

Compound Assignment Statements

n += 1

n = n + 1

Dim q As String = "Sample "
q &= "String"
' q now contains "Sample String".

Type Conversions in Assignment Statements

You can have multiple statements on a single line separated by the colon (:) character. The following example illustrates this.

Dim sampleString As String = "Hello World" : MsgBox(sampleString)

Though occasionally convenient, this form of syntax makes your code hard to read and maintain. Thus, it is recommended that you keep one statement to a line.

A statement usually fits on one line, but when it is too long, you can continue it onto the next line using a line-continuation sequence, which consists of a space followed by an underscore character (_) followed by a carriage return. In the following example, the MsgBox executable statement is continued over two lines.

Public Sub demoBox()
    Dim nameVar As String
    nameVar = "John"
    MsgBox("Hello " & nameVar _
        & ". How are you?")
End Sub

Implicit Line Continuation

Public Function GetUsername(ByVal username As String,
                            ByVal delimiter As Char,
                            ByVal position As Integer) As String

    Return username.Split(delimiter)(position)
End Function

Dim username = GetUsername(
    Security.Principal.WindowsIdentity.GetCurrent().Name,
    CChar("\"),
    1
  )

Dim customer = New Customer With {
  .Name = "Terry Adams",
  .Company = "Adventure Works",
  .Email = "terry@www.adventure-works.com"
}

Dim customerXml = <Customer>
                      <Name>
                          <%=
                              customer.Name
                          %>
                      </Name>
                      <Email>
                          <%=
                              customer.Email
                          %>
                      </Email>
                  </Customer>

cmd.CommandText = 
    "SELECT * FROM Titles JOIN Publishers " &
    "ON Publishers.PubId = Titles.PubID " &
    "WHERE Publishers.State = 'CA'"

Dim fileStream =
  My.Computer.FileSystem.
    OpenTextFileReader(filePath)

Dim memoryInUse =
  My.Computer.Info.TotalPhysicalMemory +
  My.Computer.Info.TotalVirtualMemory -
  My.Computer.Info.AvailablePhysicalMemory -
  My.Computer.Info.AvailableVirtualMemory

If TypeOf inStream Is 
  IO.FileStream AndAlso
  inStream IsNot
  Nothing Then

    ReadFile(inStream)

End If

Dim fileStream =
  My.Computer.FileSystem.
    OpenTextFileReader(filePath)


...


' Not allowed:
' Dim aType = New With { .
'    PropertyName = "Value"

' Allowed:
Dim aType = New With {.PropertyName =
    "Value"}



Dim log As New EventLog()

' Not allowed:
' With log
'    .
'      Source = "Application"
' End With

' Allowed:
With log
    .Source =
      "Application"
End With

Dim customerName = customerXml.
  <Name>.Value

Dim customerEmail = customerXml...
  <Email>.Value

<
Serializable()
>
Public Class Customer
    Public Property Name As String
    Public Property Company As String
    Public Property Email As String
End Class

Dim vsProcesses = From proc In
                    Process.GetProcesses
                  Where proc.MainWindowTitle.Contains("Visual Studio")
                  Select proc.ProcessName, proc.Id,
                         proc.MainWindowTitle

For Each p In
  vsProcesses

    Console.WriteLine("{0}" & vbTab & "{1}" & vbTab & "{2}",
      p.ProcessName,
      p.Id,
      p.MainWindowTitle)
Next

Dim days = New List(Of String) From
  {
   "Mo", "Tu", "We", "Th", "F", "Sa", "Su"
  }

Source code is not always self-explanatory, even to the programmer who wrote it. To help document their code, therefore, most programmers make liberal use of embedded comments. Comments in code can explain a procedure or a particular instruction to anyone reading or working with it later. Visual Basic ignores comments during compilation, and they do not affect the compiled code.

Comment lines begin with an apostrophe (') or REM followed by a space. They can be added anywhere in code, except within a string. To append a comment to a statement, insert an apostrophe or REM after the statement, followed by the comment. Comments can also go on their own separate line. The following example demonstrates these possibilities.

' This is a comment on a separate code line.
REM This is another comment on a separate code line.
x += a(i) * b(i) ' Add this amount to total.
MsgBox(statusMessage) REM Inform operator of status.

If, after you type a line of code, the line is displayed with a wavy blue underline (an error message may appear as well), there is a syntax error in the statement. You must find out what is wrong with the statement (by looking in the task list, or hovering over the error with the mouse pointer and reading the error message) and correct it. Until you have fixed all syntax errors in your code, your program will fail to compile correctly.

Assignment Operators

Provides links to language reference pages covering assignment operators such as =, *=, and &=.

Operators and Expressions in Visual Basic

Shows how to combine elements with operators to yield new values.

How to: Break and Combine Statements in Code

Shows how to break a single statement into multiple lines and how to place multiple statements on the same line.

How to: Label Statements

Shows how to label a line of code.