QBasic is a subset of QuickBasic version 4.5. The QBasic online help
feature contains complete articles explaining version differences between
BASICA/GW-BASIC and QBasic, unsupported keywords, and converting BASICA
programs for use under QBasic.
QBasic provides a "Windows-like" environment supporting the use of a mouse.
A menu bar across the top of the screen contains pull-down menu selections.
QBasic provides a split screen. The upper portion of the screen is called
the view window and is for program code; at the bottom of the screen, an
"immediate" window allows testing of a programming instruction prior to
including it in a program.
With QBasic, you don't need to use line numbers. However, line numbers are
supported. Also, QBasic now supports line "labels." These labels are not
required on every line, however, but can be used to direct program flow. As
a result, QBasic has no RENUM command such as that of GW-BASIC. For
Line label "Bob:" or line number "10" are both valid.
QBasic includes friendly, extensive online help. For more information about
using QBasic, press ENTER immediately after starting QBasic or press F1 any
time while running QBasic. If you are using a mouse, point to the Help menu
option on the right side of the menu bar (on the top right of the displayed
You can cut and paste examples of program code from the online help screen
and place them directly into the view window for execution.
QBasic uses IEEE floating point math, the industry standard. GW-BASIC uses
the MBF math format. For more information on IEEE vs. Microsoft Binary
Format, query on the following words:
Tutorial and IEEE and MBF
QBasic is a subset of QuickBasic 4.5. QuickBasic 4.0 and later will
support a math co-processor, however, QBasic does not.
QBasic uses P-code, which stands for "pseudo code," so called because it's
very similar to compiled code, but it's not completely compiled. P-code
retains just enough information -- the crucial last bits that real machine
code loses -- for listing it on the screen in source code format and for
any modifications you decide to make. Yet, because it looks almost like the
output of a compiler, it runs almost as fast as you would expect an
executable file to run. Consequently, you get all the advantages of using
an interpreter with virtually no speed penalty and little size penalty.
QBasic supports additional variable types: User-Defined Types, Fixed-Length
Strings, and Long Integers.
Use the type
If the variable is: declaration character:
A regular integer variable can store any whole number from -32768 through
- Use "%" to declare regular integers.
To declare a fixed-length string, add a string variable name and a string
length to the DIM statement, as follows
DIM strName AS STRING * n
where strName is the name of the fixed-length string and n is the string
A long integer variable can represent a whole number from -2,147,483,648
through 2,147,483,647. Use "&" to declare long integers.
Example: employees& = 15000000
Single-precision floating-point variables can represent a number up to
seven digits in length. The decimal point can be anywhere within those
digits. Use "!" to declare single-precision floating-point variables.
Example: speed!= 33.33333
Double-precision floating-point variables can represent a number up to
15 digits in length. The decimal point can be anywhere within those
digits. Use "#" to declare double-precision floating point variables.
Example: pi# = 3.141592654
QBasic allows 64K memory for code per subroutine and 64K for data. Arrays,
fixed-length strings, and user-defined types get 64K each. There is 64K of
memory available for CODE per SUBroutine and 64K of memory for DATA. You
can also have far arrays of numerics, fixed-length strings, and user-
defined types of up to 64K each.
QBasic allows error/event trapping:
"ON ERROR GOSUB.../ON KEY(n) GOTO..."
PRINT "You had an error!"
PRINT "Error" ERR
ON ERROR GOTO errhandler
QBasic allows variable/value parameter passing. SUB/END SUB and UNCTION/END
FUNCTION. QBasic provides a way to share arguments with a limited number of
subprograms rather than with the entire program. This method is called
FUNCTION name [parameterlist][STATIC]
name = expression
File Conversion from GW-BASIC to QBasic
To use a GW-BASIC program in QBasic, you must first save the file in an
ASCII text format.
Example: SAVE: "PROGNAME.BAS",A.
Converting a GW-BASIC Program to QBasic
Use REMLINE.BAS included with MS-DOS for QBasic to remove line numbers from
GW-BASIC programs. For more information, see the documentation provided at
the beginning of REMLINE.BAS by opening the file in QBasic.
To load GW-BASIC programs to QBasic, you must use the command "QBasic
/MBF" when starting QBasic from the DOS prompt.