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

Data Types
There are several types of data in QBasic

     strings          "dog"   "cat"  "the_boy"
     integers         1   7  -39   37   43   0
     long integer     
     single           1.2  -17.4  83.2  171.006
     double           1.109435089627097612
     user-defined     (combination of above types, see explanation below)

All QBasic variables are one of these basic data types. In performing functions which expect a particular type of data, QBasic will try, but may not succeed, to adjust the type of data found in a variable to the type needed by the function.

Data Type Value Ranges
The minimum/maximum values of each data type is given in the next table.

Date Type	Minimum	Maximum
String	0	32,767 characters
Integer	-32,768	32,767
Long	-2,147,483,648	2,147,483,647
Single	-2.8E-45	3.4E+38
Double	-4.9D-324	1.8DE+308

Conversion
In many programs a value of a specific data type is required. QBasic provides several ways to convert variables to specific data types.

To convert any number to a specific data type, use one of the following functions.

• cint
  
• clng
  
• csng
  
• cdbl
  

To convert a string to a specific data type, use one of the following functions.

• cvi
  
• cvl
  
• cvs
  
• cvd
  
• cvsmbf
  
• cvdmbf
  

User-Defined Data Type (UDT)
QBasic also supports a very useful data type which consists of more than one of the standard data types. In this example, a "Custom" data type is defined and the variable X is defined as that data type. The example shows how to assign and access the elements which make up a user-defined data type.

     Type Custom 
         a as string
         b as number
         c as double
     End Type

     Dim X as Custom

     X.a = "hello"
     X.b = 5
     X.c = 53.2429965

This technique allows you to carry multiple values around in a single variable. You can write X to a file and save all three values in a single statement.

If you have any suggestions for additions to these tutorials, please let me know.