Visual Basic for Programmers of Other Languages

Option Strict On

Module Program

    Sub Main()
        Dim line As String = "Reference"
        Dim Line As Integer = 3
        Console.WriteLine(line)
    End Sub

End Module

Program.vb(7,13): error BC30288: Local variable 'Line' is already declared in the current block.

Option Strict On

Module Program

    Structure Point2D
        Public X As Integer
        Public Y As Integer
    End Structure

    Sub Main()
        Console.WriteLine("-- names ignore case")
        Dim copies As Integer = 3
        COPIES += 1
        Console.WriteLine(Copies)
        console.writeline("still Console.WriteLine")

        Console.WriteLine("-- array declarations give the upper bound")
        Dim shelf(3) As String
        Console.WriteLine(shelf.Length & " " & shelf.GetUpperBound(0) & " " & UBound(shelf))
        Dim grid(2, 4) As Integer
        Console.WriteLine(grid.GetLength(0) & " x " & grid.GetLength(1))
        Dim shelfSlots = New String(3) {}
        Console.WriteLine(shelfSlots.Length)

        Console.WriteLine("-- = assigns in a statement and compares in an expression")
        Dim a As Integer = 5
        Dim b As Boolean = a = 5
        Dim c As Boolean = (a = 6)
        Console.WriteLine(b & " " & c)

        Console.WriteLine("-- Nothing is the default value of any type")
        Dim count As Integer = Nothing
        Dim flag As Boolean = Nothing
        Dim title As String = Nothing
        Dim origin As Point2D = Nothing
        Console.WriteLine(count & " " & flag & " [" & title & "] " & origin.X & "," & origin.Y)
        Dim empty As String = ""
        Console.WriteLine((empty = Nothing) & " " & (empty Is Nothing) & " " & String.IsNullOrEmpty(empty))

        Console.WriteLine("-- one As clause types every name in the list")
        Dim low, high As Integer
        Console.WriteLine(low.GetType().Name & " " & high.GetType().Name)
    End Sub

End Module

-- names ignore case
4
still Console.WriteLine
-- array declarations give the upper bound
4 3 3
3 x 5
4
-- = assigns in a statement and compares in an expression
True False
-- Nothing is the default value of any type
0 False [] 0,0
True False True
-- one As clause types every name in the list
Int32 Int32

Option Strict On

Module Program

    Sub Main()
        Dim copies As Integer? = Nothing
        Console.WriteLine("[" & (copies = 1).ToString() & "]")
        If copies = 1 Then
            Console.WriteLine("equal")
        ElseIf copies <> 1 Then
            Console.WriteLine("different")
        Else
            Console.WriteLine("neither: a comparison with Nothing is Nothing, not False")
        End If
        Console.WriteLine(copies.HasValue & " " & copies.GetValueOrDefault())

        Dim text As String = "a" & vbTab & "b"
        Console.WriteLine(text.Length)
        Dim quote As String = "She said ""hi"""
        Console.WriteLine(quote)
        Dim letter As Char = "x"c
        Console.WriteLine(letter)
        Dim items As Integer() = {10, 20, 30}
        Console.WriteLine(items(1))
        Dim w As Long = 5L : Dim r As Double = 1.5R : Dim m As Decimal = 2.5D : Dim s As Single = 1.5F
        Console.WriteLine(w & " " & r & " " & m & " " & s)
    End Sub

End Module

[]
neither: a comparison with Nothing is Nothing, not False
False 0
3
She said "hi"
x
20
5 1.5 2.5 1.5

Option Strict On

Module Program

    Sub Main()
        Dim flags As Integer = 5                      ' binary 101
        Console.WriteLine(flags And 3)                ' bitwise on integers (C# &)
        Console.WriteLine(flags Or 2)                 ' (C# |)
        Console.WriteLine(flags Xor 1)                ' (C# ^)
        Console.WriteLine(Not flags)                  ' bitwise complement (C# ~)
        Console.WriteLine(flags << 2)                 ' shifts exist since VB 7.1
        Console.WriteLine((flags And 1) = 1)          ' parentheses: = binds tighter than And
        Console.WriteLine("shelf" = "SHELF")          ' Option Compare Binary: case-sensitive
        Console.WriteLine("shelf" <> "Shelf")         ' <> is inequality (C# !=)
        Dim a As Object = "x"
        Dim b As Object = a
        Console.WriteLine((a Is b) & " " & (a IsNot Nothing))   ' reference equality: Is / IsNot
        Console.WriteLine(-7 Mod 3)                   ' remainder keeps the sign of the dividend
        Console.WriteLine(Math.Pow(2, 10))            ' same as 2 ^ 10
    End Sub

End Module

1
7
4
-6
20
True
False
True
True True
-1
1024

Option Strict On

Imports System.IO

' abstract class            -> MustInherit            virtual / override -> Overridable / Overrides
Public MustInherit Class CatalogItem
    Public Property Title As String
    Public Shared Count As Integer                              ' static field -> Shared

    Protected Sub New(title As String)
        Me.Title = title                                        ' this -> Me
        Count += 1
    End Sub

    Public MustOverride ReadOnly Property Kind As String
    Public Overridable Function Describe() As String
        Return Kind & ": " & Title
    End Function
End Class

Public Class Book
    Inherits CatalogItem                                        ' class Book : CatalogItem
    Public Sub New(title As String)
        MyBase.New(title)                                       ' base(title) -> MyBase.New
    End Sub
    Public Overrides ReadOnly Property Kind As String
        Get
            Return "Book"
        End Get
    End Property
End Class

Public NotInheritable Class Magazine                            ' sealed -> NotInheritable
    Inherits CatalogItem
    Friend ReadOnly Issue As Integer                            ' internal readonly -> Friend ReadOnly
    Public Sub New(title As String, issue As Integer)
        MyBase.New(title)
        Me.Issue = issue
    End Sub
    Public Overrides ReadOnly Property Kind As String
        Get
            Return "Magazine"
        End Get
    End Property
    Public Overrides Function Describe() As String
        Return MyBase.Describe() & " #" & Issue
    End Function
End Class

' static class -> Module: every member is shared, no instance can be created
Module Toolbox

    Private ReadOnly Gate As New Object()

    Iterator Function Countdown(start As Integer) As IEnumerable(Of Integer)   ' yield return -> Yield
        For i As Integer = start To 1 Step -1
            Yield i
        Next
    End Function

    Function Grade(copies As Integer) As String                 ' switch -> Select Case
        Select Case copies
            Case 0
                Return "none"
            Case 1 To 3
                Return "few"
            Case Is > 3
                Return "many"
            Case Else
                Return "invalid"
        End Select
    End Function

    Function Visits() As Integer
        Static calls As Integer                                  ' static local -> Static
        SyncLock Gate                                            ' lock (gate) -> SyncLock
            calls += 1
        End SyncLock
        Return calls
    End Function

    Function Sum(ParamArray values As Integer()) As Integer      ' params -> ParamArray
        Return values.Sum()
    End Function

    Sub Swap(ByRef a As Integer, ByRef b As Integer)             ' ref / out -> ByRef
        Dim t As Integer = a
        a = b
        b = t
    End Sub
End Module

Module Program

    Sub Main()
        Dim items As New List(Of CatalogItem) From {New Book("Atlas"), New Magazine("Nature", 7)}

        For Each item As CatalogItem In items                                 ' foreach -> For Each
            Dim asMagazine As Magazine = TryCast(item, Magazine)              ' as -> TryCast
            Console.WriteLine(item.Describe() & If(TypeOf item Is Book, " (book)", "") &
                              If(asMagazine IsNot Nothing, " issue " & asMagazine.Issue, ""))
        Next

        Dim nickname As String = Nothing
        Console.WriteLine(If(nickname, "anonymous"))                          ' ?? -> If(a, b)
        Console.WriteLine(If(CatalogItem.Count > 1, "many", "one"))           ' ?: -> If(c, a, b)
        Console.WriteLine(Toolbox.Grade(2) & " " & Toolbox.Grade(9) & " " & Toolbox.Grade(-1))
        Console.WriteLine(String.Join(",", Toolbox.Countdown(3)))
        Console.WriteLine(Toolbox.Visits() & Toolbox.Visits())
        Console.WriteLine(Toolbox.Sum(1, 2, 3))

        Dim x As Integer = 1, y As Integer = 2
        Toolbox.Swap(x, y)
        Console.WriteLine(x & " " & y)

        Dim titles = From item In items                                        ' LINQ query syntax
                     Where item.Title.Length > 5
                     Select item.Title.ToUpperInvariant()
        Console.WriteLine(String.Join(";", titles))
        Dim twice As Func(Of Integer, Integer) = Function(n) n * 2            ' (n) => n * 2
        Console.WriteLine(twice(21))

        Using writer As New StringWriter()                                     ' using (var w = ...) { }
            writer.Write("disposed at End Using")
            Console.WriteLine(writer.ToString())
        End Using
    End Sub

End Module

Book: Atlas (book)
Magazine: Nature #7 issue 7
anonymous
many
few many invalid
3,2,1
12
6
2 1
NATURE
42
disposed at End Using

Option Strict On

Public Class Loan
    Public Event Returned As EventHandler                      ' public event EventHandler Returned;

    Public Sub [Return]()
        RaiseEvent Returned(Me, EventArgs.Empty)                ' Returned?.Invoke(this, EventArgs.Empty)
    End Sub
End Class

Public Class Desk
    Private WithEvents _loan As New Loan()                      ' a field that raises events, handled by name

    Private Sub OnReturned(sender As Object, e As EventArgs) Handles _loan.Returned
        Console.WriteLine("Handles clause: loan returned")
    End Sub

    Public Sub Run()
        Dim extra As EventHandler = Sub(s, e) Console.WriteLine("AddHandler lambda: loan returned")
        AddHandler _loan.Returned, extra                         ' _loan.Returned += extra
        _loan.Return()
        RemoveHandler _loan.Returned, extra                      ' _loan.Returned -= extra
        _loan.Return()
    End Sub
End Class

Module Program

    Sub Main()
        Call New Desk().Run()

        Dim title As String = "Atlas"
        Dim book As XElement = <book year="1999">
                                   <title><%= title %></title>
                                   <author>Ada</author>
                               </book>
        Console.WriteLine(book.@year & " " & book.<title>.Value)
        Console.WriteLine(book)
    End Sub

End Module

Handles clause: loan returned
AddHandler lambda: loan returned
Handles clause: loan returned
1999 Atlas
<book year="1999">
  <title>Atlas</title>
  <author>Ada</author>
</book>