Visual Basic (.NET)

Visual Basic, originally called Visual Basic .NET (VB.NET), is a multi-paradigm, object-oriented programming language, implemented on .NET, Mono, and the .NET Framework. Microsoft launched VB.NET in 2002 as the successor to its original Visual Basic language, the last version of which was Visual Basic 6.0. Although the ".NET" portion of the name was dropped in 2005, this article uses "Visual Basic NET to refer to all Visual Basic languages released since 2002, in order to distinguish between them and the classic Visual Basic. Along with C# and F#, it is one of the three main languages targeting the .NET ecosystem. As of March 11, 2020, Microsoft announced that evolution of the VB.NET language has concluded.

Microsoft's integrated development environment (IDE) for developing in Visual Basic is Visual Studio. Most Visual Studio editions are commercial; the only exceptions are Visual Studio Express and Visual Studio Community, which are freeware. In addition, the .NET Framework SDK includes a freeware command-line compiler called vbc.exe. Mono also includes a command-line VB.NET compiler.

Visual Basic is often used in conjunction with the Windows Forms GUI library to make desktop apps for Windows. Programming for Windows Forms with Visual Basic involves dragging and dropping controls on a form using a GUI designer and writing corresponding code for each control.

Syntax

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 three iterative execution (loop) constructs (Do ... Loop, For ... To, and For Each) . 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't 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 and/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, one could use 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 ", 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(" ", 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