Fundamentals Overview IDE (Editor) Syntax Variables Data Types Declarations Scope Operators

Standard Functions Arithmetic Trigonometry Strings Arrays Date/Time Flow Control Procedures Printing Files Folders

Additional Capabilities Keyboard Sound Graphics Concepts Screen (text) Screen (drawing) Gaming (sprites) Event Trapping Errors System Calls

Variables
Like all languages, QBasic uses variables to store values. In QBasic all variables begin with a letter (A-Z). The variable names can also contain the number 0-9 or a period. Variable names can be up to 40 characters long.

Creating a Variable
Unlike some languages which require that you define a variable before using it, QBasic allows you to define a variable by simply using it in a line of code.

     a$ = 5      # a$ is created simply by assigning it a value

When a variable has not yet been assigned a value, QBasic sets the value to 0 for numbers or to "" for strings.

Variable Declaration
Instead of creating a variable by simply using it, a variable can also be declared using one of the following methods. Discussion of how to use these is found in the Variable Declaration page.

Variable Declaration	dim, redim, const
By-Letter Typing	defint, defdbl, defsng, defstr, deflng
Scope Control	static, shared
User-Defined Type	type

Initial Values
QBasic will assign numbers an initial, default value of zero and strings a default value of "" (empty string).

Case Sensitivity
QBasic is not case-sensitive. The variables dog$ and DOG$ refer to the same variable.

Note: the QBasic IDE will detect variations on capitalization of variable names and modify the source code so that all variables of the same name are capitalized the same way. The first instance of the spelling is used for the template to changes all subsequent instances of the variable name.

Good Practice
Using variable names which describe the content of the variable is considered good practice. For example, size$ is preferred over s$.

Programmers often use the following naming practice for variables, which involves using more than one word in the variable name.

     LastIndex      # capitalize first letter of words within a variable name