QBasic is an interpreter for the BASIC programming language. It is included in MS DOS and Windows as part of the base operating system. Unlike early versions of BASIC, QBasic was a structured programming language, supporting constructs such as named subroutines and while loops. Line numbers, a concept often associated with BASIC, were supported but weren't considered good form.
QBasic was produced by Microsoft and bundled in MS DOS 3.3 (and possibly other versions as well). Microsoft stopped shipping QBasic with later versions of Windows (Windows_98 users for example will find it in the tools/oldmsdos/ directory of the Windows_98 CD-ROM) and it is no longer available. QBasic provided a state-of-the-art IDE (for its time), including a debugger with features such as on-the-fly expression evaluation and code modification that were still relatively unusual in 2003, more than ten years later.
QBasic was based on Microsoft's Professional Development System Basic, also known as PDS Basic or simply PDS. PDS Basic was followed by Visual Basic for DOS and its language engine was likely the foundation for Microsoft's market-leading Visual Basic for Windows.
QBasic has also made its way into several third-party tools, such as the XBasic compiler and PowerBasic series of compilers. QBasic was also the subject of Beginning Programming For Dummies.
