Visual Basic uses
statements to specify actions. The most common statement is an expression statement, consisting of an
expression to be evaluated, on a single line. As part of that evaluation,
functions or subroutines may be
called and
variables may be
assigned new values. To modify the normal sequential execution of statements, Visual Basic provides several control-flow statements identified by reserved keywords.
Structured programming is supported by several constructs including two conditional execution constructs (If ... Then ... Else ... End If and Select Case ... Case ... End Select ) and four iterative execution (loop) constructs (Do ... Loop, For ... To, For Each, and While ... End While) . The For ... To statement has separate initialisation and testing sections, both of which must be present. (See examples below.) The For Each statement steps through each value in a list. In addition, in Visual Basic: • There is no unified way of defining blocks of statements. Instead, certain keywords, such as "If ... Then" or "Sub" are interpreted as starters of sub-blocks of code and have matching termination keywords such as "End If" or "End Sub". • Statements are terminated either with a
colon (":") or with the
end of line. Multiple-line statements in Visual Basic are enabled with " _" at the end of each such line. The need for the underscore continuation character was largely removed in version 10 and later versions. • The
equals sign ("=") is used in both assigning values to variables and in comparison. •
Round brackets (parentheses) are used with
arrays, both to declare them and to get a value at a given index in one of them. Visual Basic uses round brackets to define the parameters of subroutines or functions. • A
single quotation mark (') or the keyword REM, placed at the beginning of a line or after any number of
space or
tab characters at the beginning of a line, or after other code on a line, indicates that the (remainder of the) line is a
comment.
Simple example The following is a very simple Visual Basic program, a version of the classic "
Hello, World!" example created as a console application: Module Module1 Sub Main() ' The classic "Hello, World!" demonstration program Console.WriteLine("Hello, World!") End Sub End Module It prints "
Hello, World!" on a
command-line window. Each line serves a specific purpose, as follows: Module Module1 This is a module definition. Modules are a division of code, which can contain any kind of object, like constants or variables, functions or methods, or classes, but can not be instantiated as objects like classes and cannot inherit from other modules. Modules serve as containers of code that can be referenced from other parts of a program.It is common practice for a module and the code file which contains it to have the same name. However, this is not required, as a single code file may contain more than one module or class. Sub Main() This line defines a subroutine called "Main". "Main" is the entry point, where the program begins execution. Console.WriteLine("Hello, world!") This line performs the actual task of writing the output.
Console is a system object, representing a command-line interface (also known as a "console") and granting programmatic access to the operating system's
standard streams. The program calls the
Console method
WriteLine, which causes the string passed to it to be displayed on the console. Instead of Console.WriteLine, an alternative is MsgBox, which prints the message in a dialog box instead of a command-line window.
Complex example This piece of code outputs
Floyd's Triangle to the console: Imports System.Console Module Program Sub Main() Dim rows As Integer ' Input validation. Do Until Integer.TryParse(ReadLine("Enter a value for how many rows to be displayed: " & vbcrlf), rows) AndAlso rows >= 1 WriteLine("Allowed range is 1 and {0}", Integer.MaxValue) Loop ' Output of Floyd's Triangle Dim current As Integer = 1 Dim row As Integer Dim column As Integer For row = 1 To rows For column = 1 To row Write("{0,-2} ", current) current += 1 Next WriteLine() Next End Sub ''' ''' Like Console.ReadLine but takes a prompt string. ''' Function ReadLine(Optional prompt As String = Nothing) As String If prompt IsNot Nothing Then Write(prompt) End If Return Console.ReadLine() End Function End Module
Comparison with the classic Visual Basic Whether Visual Basic .NET should be considered as just another version of Visual Basic or a completely different language is a topic of debate. There are new additions to support new features, such as
structured exception handling and short-circuited expressions. Also, two important data-type changes occurred with the move to VB.NET: compared to Visual Basic 6, the
Integer data type has been doubled in length from 16 bits to 32 bits, and the Long
data type has been doubled in length from 32 bits to 64 bits. This is true for all versions of VB.NET. A 16-bit integer in all versions of VB.NET is now known as a Short. Similarly, the
Windows Forms editor is very similar in style and function to the Visual Basic form editor. The things that
have changed significantly are the semantics—from those of an object-based programming language running on a
deterministic,
reference-counted engine based on
COM to a fully
object-oriented language backed by the
.NET Framework, which consists of a combination of the
Common Language Runtime (a
virtual machine using
generational garbage collection and a
just-in-time compilation engine) and a far larger
class library. The increased breadth of the latter was also a problem that VB developers had to deal with when coming to the language, although this was somewhat addressed by the
My feature in Visual Studio 2005. The changes altered many underlying assumptions about the "right" thing to do with respect to the performance and maintainability of applications. Some functions and libraries no longer exist; others are available, but not as efficient as the "native" .NET alternatives. Even if they compiled, most converted Visual Basic 6 applications required some level of
refactoring to take full advantage of the .NET language. Microsoft provided documentation to cover changes in language syntax, debugging applications, deployment, and terminology. A popular trade book designed to ease the transition was
Michael Halvorson's Microsoft Visual Basic .NET Professional Step by Step, published in 2002 by
Microsoft Press.
Comparative examples The following simple examples compare VB and VB.NET syntax. They assume that the developer has created a form, placed a button on it and has associated the subroutines demonstrated in each example with the click
event handler of the mentioned button. Each example creates a "Hello, World" message box after the button on the form is clicked. Visual Basic 6: Private Sub Command1_Click() MsgBox "Hello, World" End Sub VB.NET (MsgBox or MessageBox class can be used): Private Sub Button1_Click(sender As object, e As EventArgs) Handles Button1.Click MsgBox("Hello, World") End Sub • Both Visual Basic 6 and Visual Basic .NET automatically generate the Sub and End Sub statements when the corresponding button is double-clicked in design view. Visual Basic .NET will also generate the necessary Class and End Class statements. The developer need only add the statement to display the "Hello, World" message box. • All procedure calls must be made with parentheses in VB.NET, whereas in Visual Basic 6 there were different conventions for functions (parentheses required) and subs (no parentheses allowed, unless called using the keyword Call). • The names Command1 and Button1 are not obligatory. However, these are default names for a command button in Visual Basic 6 and VB.NET respectively. • In VB.NET, the Handles keyword is used to make the sub Button1_Click a handler for the Click event of the object Button1. In Visual Basic 6, event handler subs must have a specific name consisting of the object's name (), an underscore (), and the event's name (, hence ). • There is a function called MessageBox.Show in the Microsoft.VisualBasic namespace which can be used (instead of MsgBox) similarly to the corresponding function in Visual Basic 6. There is a controversy about which function to use as a best practice (not only restricted to showing message boxes but also regarding other features of the Microsoft.VisualBasic namespace). Some programmers prefer to do things "the .NET way", since the Framework classes have more features and are less language-specific. Others argue that using language-specific features makes code more readable (for example, using int (C#) or Integer (VB.NET) instead of System.Int32). • In Visual Basic 2008, the inclusion of , has become optional. The following example demonstrates a difference between Visual Basic 6 and VB.NET. Both examples close the
active window. Visual Basic 6: Sub cmdClose_Click() Unload Me End Sub VB.NET: Sub btnClose_Click(sender As Object, e As EventArgs) Handles btnClose.Click Close() End Sub The 'cmd' prefix is replaced by the 'btn' prefix, conforming to the new convention previously mentioned. Visual Basic 6 did not provide common operator shortcuts. The following are equivalent: Visual Basic 6: Sub Timer1_Timer() 'Reduces Form Height by one pixel per tick Me.Height = Me.Height - 1 End Sub VB.NET: Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick Me.Height -= 1 End Sub
Comparison with C# C# and Visual Basic are Microsoft's first languages made to program on the .NET Framework (later adding
F# and more; others have also added languages). Though C# and Visual Basic are syntactically different, that is where the differences mostly end. Microsoft developed both of these languages to be part of the same .NET Framework development platform. They are both developed, managed, and supported by the same language development team at Microsoft. They compile to the same intermediate language (IL) known as
CIL, which runs against the same .NET Framework runtime libraries. Although there are some differences in the programming constructs, their differences are primarily syntactic and, assuming one avoids the Visual Basic "Compatibility" libraries provided by Microsoft to aid conversion from Visual Basic 6, almost every feature in VB has an equivalent feature in C# and vice versa. Both languages reference the same Base Classes of the .NET Framework to extend their functionality, and both languages can reference compiled code written in the other language. As a result, with few exceptions, a program written in either language can be run through a simple syntax converter to translate to the other. There are many open source and commercially available products for this task. == Examples ==