Visual Basic

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This article is about the Visual Basic language shipping with Microsoft Visual Studio 6.0 or earlier. For the Visual Basic language shipping with Microsoft Visual Studio .NET or later, see Visual Basic .NET.
Visual Basic
The four colored boxes is the logo of VBA, and the two drums above them symbolize database connectivity
Paradigm Event-driven
Developer Microsoft
Latest release VB6/ 1998
Typing discipline Static, strong
Influenced by QuickBASIC
Influenced Visual Basic .NET, Gambas
OS Microsoft Windows, MS-DOS

Visual Basic (VB) is a third-generation event-driven programming language and associated development environment (IDE) from Microsoft for its COM programming model. VB is also considered a relatively easy to learn and use programming language, because of its graphical development features and BASIC heritage.[1]

Visual Basic was derived from BASIC and enables the rapid application development (RAD) of graphical user interface (GUI) applications, access to databases using Data Access Objects DAO, Remote Data Objects RDO, or ActiveX Data Objects ADO, and creation of ActiveX controls and objects. Scripting languages such as VBA and VBScript are syntactically similar to Visual Basic, but perform differently.[2]

A programmer can put together an application using the components provided with Visual Basic itself. Programs written in Visual Basic can also use the Windows API, but doing so requires external function declarations.

The final release was version 6 in 1998. Microsoft's extended support ended in March 2008 and the designated successor was Visual Basic .NET.

Contents

Language features

Like the BASIC programming language, Visual Basic was designed to be easy to learn and use. The language not only allows programmers to create simple GUI applications, but can also develop complex applications. Programming in VB is a combination of visually arranging components or controls on a form, specifying attributes and actions of those components, and writing additional lines of code for more functionality. Since default attributes and actions are defined for the components, a simple program can be created without the programmer having to write many lines of code. Performance problems were experienced by earlier versions, but with faster computers and native code compilation this has become less of an issue.

Although programs can be compiled into native code executables from version 5 onwards, they still require the presence of runtime libraries of approximately 2 MB in size. This runtime is included by default in Windows 2000 and later, but for earlier versions of Windows or Windows Vista, it must be distributed together with the executable.

Forms are created using drag and drop techniques. A tool is used to place controls (e.g., text boxes, buttons, etc.) on the form (window). Controls have attributes and event handlers associated with them. Default values are provided when the control is created, but may be changed by the programmer. Many attribute values can be modified during run time based on user actions or changes in the environment, providing a dynamic application. For example, code can be inserted into the form resize event handler to reposition a control so that it remains centered on the form, expands to fill up the form, etc. By inserting code into the event handler for a keypress in a text box, the program can automatically translate the case of the text being entered, or even prevent certain characters from being inserted.

Visual Basic can create executables (EXE files), ActiveX controls, DLL files, but is primarily used to develop Windows applications and to interface web database systems. Dialog boxes with less functionality can be used to provide pop-up capabilities. Controls provide the basic functionality of the application, while programmers can insert additional logic within the appropriate event handlers. For example, a drop-down combination box will automatically display its list and allow the user to select any element. An event handler is called when an item is selected, which can then execute additional code created by the programmer to perform some action based on which element was selected, such as populating a related list.

Alternatively, a Visual Basic component can have no user interface, and instead provide ActiveX objects to other programs via Component Object Model (COM). This allows for server-side processing or an add-in module.

The language is garbage collected using reference counting, has a large library of utility objects, and has basic object oriented support. Since the more common components are included in the default project template, the programmer seldom needs to specify additional libraries. Unlike many other programming languages, Visual Basic is generally not case sensitive, although it will transform keywords into a standard case configuration and force the case of variable names to conform to the case of the entry within the symbol table entry. String comparisons are case sensitive by default, but can be made case insensitive if so desired.

The Visual Basic compiler is shared with other Visual Studio languages (C, C++), but restrictions in the IDE do not allow the creation of some targets (Windows model DLL's) and threading models.

Characteristics present in Visual Basic

Visual Basic has the following traits which differ from C-derived languages:

  • Boolean constant True has numeric value −1.[3] This is because the Boolean data type is stored as a 16-bit signed integer. In this construct −1 evaluates to 16 binary 1s (the Boolean value True), and 0 as 16 0s (the Boolean value False). This is apparent when performing a Not operation on a 16 bit signed integer value 0 which will return the integer value −1, in other words True = Not False. This inherent functionality becomes especially useful when performing logical operations on the individual bits of an integer such as And, Or, Xor and Not.[4] This definition of True is also consistent with BASIC since the early 1970s Microsoft BASIC implementation and is also related to the characteristics of microprocessor instructions at the time.
  • Logical and bitwise operators are unified. This is unlike all the C-derived languages (such as Java or Perl), which have separate logical and bitwise operators. This again is a traditional feature of BASIC.
  • Variable array base. Arrays are declared by specifying the upper and lower bounds in a way similar to Pascal and Fortran. It is also possible to use the Option Base statement to set the default lower bound. Use of the Option Base statement can lead to confusion when reading Visual Basic code and is best avoided by always explicitly specifying the lower bound of the array. This lower bound is not limited to 0 or 1, because it can also be set by declaration. In this way, both the lower and upper bounds are programmable. In more subscript-limited languages, the lower bound of the array is not variable. This uncommon trait does exist in Visual Basic .NET but not in VBScript.
OPTION BASE was introduced by ANSI, with the standard for ANSI Minimal BASIC in the late 1970s.
  • Relatively strong integration with the Windows operating system and the Component Object Model.
  • Banker's rounding as the default behavior when converting real numbers to integers with the Round function.
  • Integers are automatically promoted to reals in expressions involving the normal division operator (/) so that division of an odd integer by an even integer produces the intuitively correct result. There is a specific integer divide operator (\) which does truncate.
  • By default, if a variable has not been declared or if no type declaration character is specified, the variable is of type Variant. However this can be changed with Deftype statements such as DefInt, DefBool, DefVar, DefObj, DefStr. There are 12 Deftype statements in total offered by Visual Basic 6.0. The default type may be overridden for a specific declaration by using a special suffix character on the variable name (# for Double, ! for Single, & for Long, % for Integer, $ for String, and @ for Currency) or using the key phrase As (type). VB can also be set in a mode that only explicitly declared variables can be used with the command Option Explicit.

Evolution of Visual Basic

VB 1.0 was introduced in 1991. The drag and drop design for creating the user interface is derived from a prototype form generator developed by Alan Cooper and his company called Tripod. Microsoft contracted with Cooper and his associates to develop Tripod into a programmable form system for Windows 3.0, under the code name Ruby (no relation to the Ruby programming language).

Tripod did not include a programming language at all. Microsoft decided to combine Ruby with the Basic language to create Visual Basic.

The Ruby interface generator provided the "visual" part of Visual Basic and this was combined with the "EB" Embedded BASIC engine designed for Microsoft's abandoned "Omega" database system. Ruby also provided the ability to load dynamic link libraries containing additional controls (then called "gizmos"), which later became the VBX interface[5].

Timeline of Visual Basic (VB1 to VB6)

  • Project 'Thunder' was initiated
  • Visual Basic 1.0 (May 1991) was released for Windows at the Comdex/Windows World trade show in Atlanta, Georgia.
VB DOS Logo
Visual Basic for MS-DOS
Visual Basic for MS-DOS
  • Visual Basic 1.0 for DOS was released in September 1992. The language itself was not quite compatible with Visual Basic for Windows, as it was actually the next version of Microsoft's DOS-based BASIC compilers, QuickBASIC and BASIC Professional Development System. The interface used the "COW" (Character Oriented Windows) interface, using extended ASCII characters to simulate the appearance of a GUI.
  • Visual Basic 2.0 was released in November 1992. The programming environment was easier to use, and its speed was improved. Notably, forms became instantiable objects, thus laying the foundational concepts of class modules as were later offered in VB4.
  • Visual Basic 3.0 was released in the summer of 1993 and came in Standard and Professional versions. VB3 included version 1.1 of the Microsoft Jet Database Engine that could read and write Jet (or Access) 1.x databases.
  • Visual Basic 4.0 (August 1995) was the first version that could create 32-bit as well as 16-bit Windows programs. It also introduced the ability to write non-GUI classes in Visual Basic. Incompatibilities between different releases of VB4 caused installation and operation problems. While previous versions of Visual Basic had used VBX controls, Visual Basic now used OLE controls (with files names ending in .OCX) instead. These were later to be named ActiveX controls.
  • With version 5.0 (February 1997), Microsoft released Visual Basic exclusively for 32-bit versions of Windows. Programmers who preferred to write 16-bit programs were able to import programs written in Visual Basic 4.0 to Visual Basic 5.0, and Visual Basic 5.0 programs can easily be converted with Visual Basic 4.0. Visual Basic 5.0 also introduced the ability to create custom user controls, as well as the ability to compile to native Windows executable code, speeding up calculation-intensive code execution. A free, downloadable Control Creation Edition was also released for creation of ActiveX controls. It was also used as an introductory form of Visual Basic: a regular .exe project could be created and run in the IDE, but not compiled.
  • Visual Basic 6.0 (Mid 1998) improved in a number of areas [6] including the ability to create web-based applications. VB6 has entered Microsoft's "non-supported phase" as of March 2008.
  • Mainstream Support for Microsoft Visual Basic 6.0 ended on March 31, 2005. Extended support ended in March 2008.[7] In response, the Visual Basic user community expressed its grave concern and lobbied users to sign a petition to keep the product alive.[8] Microsoft has so far refused to change their position on the matter. Ironically, around this time (2005), it was exposed that Microsoft's new anti-spyware offering, Microsoft AntiSpyware (part of the GIANT Company Software purchase), was coded in Visual Basic 6.0.[9]Its replacement, Windows Defender, was rewritten as C++/CLI code.[10]

Derivative languages

Microsoft has developed derivatives of Visual Basic for use in scripting. Visual Basic itself is derived heavily from BASIC, and subsequently has been replaced with a .NET platform version.

Some of the derived languages are:

Performance and other issues

Earlier counterparts of Visual Basic (prior to version 5) compiled the code to P-Code or Pseudo code only. Visual Basic 5 and 6 are able to compile the code to either native or P-Code as the programmer chooses. The P-Code is interpreted by the language runtime, also known as virtual machine, implemented for benefits such as portability and small code. However, it usually slows down the execution by adding an additional layer of interpretation of code by the runtime although small amounts of code and algorithms can be constructed to run faster than the compiled native code. Visual Basic applications require Microsoft Visual Basic runtime MSVBVMxx.DLL, where xx is the relevant version number, either 50 or 60. MSVBVM60.dll comes as standard with Windows in all editions after Windows 98 while MSVBVM50.dll comes with all editions after Windows 95. A Windows 95 machine would however require inclusion with the installer of whichever dll was needed by the program.

Legacy Development and Support

All versions of Visual Basic from 1.0 to 6.0 have been retired and are now unsupported by Microsoft. Visual Basic 6 programs can still run on Windows versions up to and including Vista. Development and maintenance development for Visual Basic 6 is possible on Windows XP and Windows 2003 using Visual Studio 6.0. Documentation for Visual Basic 6.0, its application programming interface and tools is best covered in the last MSDN release before Visual Studio.NET 2002. Later releases of MSDN focused on .NET development and had significant parts of the Visual Basic 6.0 programming documentation removed. Development for this type of legacy system is typically done using a virtual machine with Windows 2003 or Windows XP, Visual Studio 6.0 and MSDN documentation. As of August 2008, both Visual Studio 6.0 and the MSDN documentation mentioned above are available for download by MSDN subscribers.

Example code

Here are some examples of the language:

Program to display a pop-up message box with the words "Hello, World!" on it:

Private Sub Form_Load()
    MsgBox "Hello, World!"
End Sub

Program to display an input box:

Sub Main()
    Dim a As String
    a = InputBox("Enter your name:")
    MsgBox a
End Sub

Running Another Application Using Visual Basic:

Private Sub Run_Notepad()
    Shell "notepad.exe", vbMinimizedFocus
    'opens notepad
End Sub

Printing multiplication table of 5 on form:

Private Sub PrintMul_Click()
    Dim I As Integer
    For I = 1 To 10
        Print 5; " x "; I; " = "; 5 * I
    Next I
End Sub

Displaying all prime numbers below 100:

Private Sub DisplayPrimeNumbers()
 
    Dim Num As Long
    Dim NN As Long
    Dim IsPrime As Boolean
 
    For Num = 2 To 100
        IsPrime = True
        For NN = 2 To Int(Num / 2)
            If Num Mod NN = 0 Then
                IsPrime = False
                Exit For
            End If
        Next
        If IsPrime Then
            MsgBox CStr(Num) + " is a prime number!"
        End If
    Next
 
End Sub

Printing the string in reverse format

Private Sub DisplayReverseText(Byval Text as string)
 
    Dim i As Long
 
    For i = len(text) to 1 Step -1
        Print Mid(Text, i, 1);
    Next
 
    print
End Sub


For more details on this topic, see Wikibooks:Visual Basic.

See also

References

  1. ^ VB has been deprecated in favor of Visual Basic .NET, although conversion from VB to VB .NET can be non-trivial. [1].)
  2. ^ For example: S="ABC" : S = S & "DEF" : S = S & "GHI" is common practice in VB, but will cause major problems if used on ASP pages. This is because static constants are handled differently by the two languages. The above code will cause significant overhead for VBScript.
  3. ^ In most languages, True is mapped to a non zero numeric value, often 1 or -1.
  4. ^ Microsoft Basic Logical Expression Evaluation
  5. ^ "The Birth of Visual Basic".
  6. ^ www.insteptech.com (2005-07-22). "What's new in VB6?". www.insteptech.com.
  7. ^ Product Family Life Cycle Guidelines for Visual Basic 6.0
  8. ^ Petition to Microsoft
  9. ^ Andrew Orlowski and Carey Bishop (2005-07-22). "MS Anti-Spyware built on MS Abandonware". The Register. Retrieved on 2006-10-04.
  10. ^ Paul Thurrott's SuperSite for Windows: Windows Defender Beta 2 Review
  11. ^ Piquet, Lori (2002-02-20). "Abandoning the Fantasy of VB Migration Wizardry". DevX.com. Jupitermedia. Retrieved on 2007-05-17.

External links

Wikibooks
Wikibooks has a book on the topic of
BASIC Programming Language
Classical
Procedure-oriented
With object extensions
FreeBASIC · Gambas · RapidQ · REALbasic · StarOffice Basic · Visual Basic · Visual Basic .NET
Retrieved from "http://en.wikipedia.org/wiki/Visual_Basic"

This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.

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