QBasic

QBasic is an integrated development environment (IDE) and interpreter for a variety of dialects of BASIC which are based on QuickBASIC. Code entered into the IDE is compiled to an intermediate representation (IR), and this IR is immediately interpreted on demand within the IDE.
Like QuickBASIC, but unlike earlier versions of Microsoft BASIC, QBasic is a structured programming language, supporting constructs such as subroutines. Line numbers, a concept often associated with BASIC, are supported for compatibility, but are not considered good form, having been replaced by descriptive line labels. QBasic has limited support for user-defined data types (structures), and several primitive types used to contain strings of text or numeric data. It supports various inbuilt functions.
For its time, QBasic provided a state-of-the-art IDE, including a debugger with features such as on-the-fly expression evaluation and code modification.
History.
QBasic was intended as a replacement for GW-BASIC. It was based on the earlier QuickBASIC 4.5 compiler but without QuickBASIC's compiler and linker elements. Version 1.0 was shipped together with MS-DOS 5.0 and higher, as well as Windows 95, Windows NT 3.x, and Windows NT 4.0. IBM recompiled QBasic and included it in PC DOS 5.x, as well as OS/2 2.0 onwards. eComStation and ArcaOS, descended from OS/2 code, include QBasic 1.0. QBasic 1.1 is included with MS-DOS 6.x, and, without codice_1, in Windows 95, Windows 98 and Windows Me. Starting with Windows 2000, Microsoft no longer includes QBasic with their operating systems, but still makes it available for use on newer versions of Windows.
Contents.
QBasic (as well as the built-in MS-DOS Editor) is backwards-compatible with DOS releases prior to 5.0 (down to at least DOS 3.20). However, if used on any 8088/8086 computers, or on some 80286 computers, the QBasic program may run very slowly, or perhaps not at all, due to DOS memory size limits. Until MS-DOS 7, MS-DOS Editor and Help required QBasic: the codice_2 and codice_3 programs simply started QBasic in editor and help mode only, and these can also be entered by running codice_4 with the codice_5 and codice_6 switches (i.e., command lines codice_7 and codice_8).
QBasic came complete with four pre-written example programs. These were "Nibbles", a variant of the Snake game; "Gorillas", an Artillery game; "MONEY MANAGER", a personal finance manager; and "RemLine", a Q-BASIC code line-number-removing program.
QBasic has an Easter egg accessed by pressing and holding simultaneously after running QBasic at the DOS prompt but before the title screen loads: this lists "The Team" of programmers.