Visual Basic (classic)

Overview

Features

• Enables rapid application development of graphical user interface applications, access to databases using Jet Data Access Objects, Remote Data Objects, or ActiveX Data Object, and creation of ActiveX controls and COM objects.
• Supports event-driven programming
• Allows use of the Windows API via an external function declaration technology
• Supports sharing and reuse via the COM component technology. A programmer can create an application using components provided by VB, developed internally or from third parties. Over time the development community produced and shared many components.
• Unlike older BASIC variants, instead of requiring line numbers to support branching, code is grouped into named blocks delimited by Sub...End Sub or Function...End Function. VB retains line number support
• Code statements have no terminating character other than a line ending, and versions since 3 allow for multi-line statements for concatenation of strings or explicitly using the underscore character at the end of a line
• A code comment is denoted by a single apostrophe character, like:
• Looping statement blocks begin and end with keywords: Do...Loop, While...End While, For...Next
• Chained variable assignment is not allowed; for example A = B = C does not result in the values of A, B and C being equal. The Boolean result of "is B equal to C?" is stored in A
• Like other BASIC variants, but unlike many other languages that use 1, Boolean True has numeric value −1. VB stores a Boolean as a two's complement signed integer with all ones in binary for true and zero for false. This is apparent when performing a Not operation on the two's complement value 0, which returns the two's complement 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 CPU instructions at the time.
• Logical and bitwise operators are unified. This is unlike some C-derived languages, which have separate logical and bitwise operators. This is a traditional feature of BASIC.
• Unlike for many languages which use zero for the lower bound of an array, VB allows the lower bound to be any value like in Pascal and Fortran. The Option Base statement can be used to set the default lower bound, but some claim that its use leads to confusion when reading code and is best avoided by always explicitly specifying the lower bound. This uncommon language 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.
• Tightly bound to the Windows operating system and the Component Object Model. The native types for strings and arrays are the dedicated COM types, BSTR and SAFEARRAY.
• Banker's rounding as the default behavior when converting real numbers to integers with the Round function. ? Round gives 2, ? Round gives 4.
• An integer type value is automatically promoted to a floating point type in expressions that involve the normal division operator so that division of one integer by another produces a result that may seem more intuitive from a mathematical perspective. VB provides an integer divide operator that does truncate.
• By default, if a variable has not been declared or if no type declaration character is specified, it acts like a 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 or using the key phrase As . VB can be set up to require variable declarations via Option Explicit.

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