Language features

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 as well. 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 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 (e.g., no maximize/minimize control) 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 uncommon traits:

• Boolean constant True has numeric value −1.^[4] 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. 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 not exist in Visual Basic .NET and VBScript.

OPTION BASE was introduced by ANSI, with the standard for ANSI Minimal BASIC in the late 1970s. The extension to using a form of DIM A(1976 TO 2020) was first introduced in BBC Basic, found on the BBC micro, which in turn was influenced by COMAL.

• 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 approach for connecting the programming language to the graphical user interface is derived from a prototype developed by Alan Cooper called Tripod. Microsoft contracted with Cooper and his associates to develop Tripod into a programmable shell 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, and Ruby contained only a rudimentary command processor sufficient for its role as a Windows shell. Microsoft decided to use the simple Program Manager shell for Windows 3.0 instead of Ruby, and combine Ruby with the Basic language to create Visual Basic.

Ruby provided the "visual" part of Visual Basic — the form designer and editing tools — along with the ability to load dynamic link libraries containing additional controls (then called "gizmos"). Ruby's extensible gizmos later became the VBX interface.

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.

• 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 was textual, 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.
• 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.
• Visual Basic 6.0 (Mid 1998) improved in a number of areas^{[citation needed]}, including the ability to create web-based applications. VB6 is currently scheduled to enter Microsoft's "non-supported phase" starting March 2008.
• Mainstream Support for Microsoft Visual Basic 6.0 ended on March 31, 2005. Extended support will end in March 2008.^[5] In response, the Visual Basic user community expressed its grave concern and lobbied users to sign a petition to keep the product alive.^[6] Microsoft has so far refused to change their position on the matter. Ironically, around this time, 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.^[7] Windows Defender Beta 2 was rewritten as C++/CLI code.^[8]

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:

• Visual Basic for Applications (VBA) is included in many Microsoft applications (Microsoft Office), and also in many third-party products like AutoCAD, WordPerfect Office 2002 and ArcGIS. There are small inconsistencies in the way VBA is implemented in different applications, but it is largely the same language as VB6 and uses the same runtime library.
• VBScript is the default language for Active Server Pages. It can be used in Windows scripting and client-side web page scripting. Although it resembles VB in syntax, it is a separate language and it is executed by vbscript.dll as opposed to the VB runtime. ASP and VBScript should not be confused with ASP.NET which uses the .Net Framework for compiled web pages.
• Visual Basic .NET is Microsoft's designated successor to Visual Basic 6.0, and is part of Microsoft's .NET platform. Visual Basic.Net compiles and runs using the .NET Framework. It is not backwards compatible with VB6. An automated conversion tool exists, but for many projects automated conversion is impossible.^[9]

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 that which ever dll was needed by the program was included with the installer.