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The following describes the basic use of variables in LibreOffice Basic.
Naming Conventions for Variable Identifiers
A variable name can consist of a maximum of 255 characters. The first character of a variable name must be a letter AZ or az. Numbers can also be used in a variable name, but punctuation symbols and special characters are not permitted, with exception of the underscore character ("_"). In LibreOffice Basic variable identifiers are not casesensitive. Variable names may contain spaces but must be enclosed in square brackets if they do.
Examples for variable identifiers:
MyNumber=5 'Correct'
MyNumber5=15 'Correct'
MyNumber_5=20 'Correct'
My Number=20 'Not valid, variable with space must be enclosed in square brackets'
[My Number]=12 'Correct'
DéjàVu=25 'Not valid, special characters are not allowed'
5MyNumber=12 'Not valid, variable may not begin with a number'
Number,Mine=12 'Not valid, punctuation marks are not allowed'
Declaring Variables
In LibreOffice Basic you don't need to declare variables explicitly. A variable declaration can be performed with the Dim statement. You can declare more than one variable at a time by separating the names with a comma. To define the variable type, use either a typedeclaration sign after the name, or the appropriate key word.
Examples for variable declarations:
Dim a$ 'Declares the variable "a" as a String'
Dim a As String 'Declares the variable "a" as a String'
Dim a$, b As Integer 'Declares one variable as a String and one as an Integer'
Dim c As Boolean 'Declares c as a Boolean variable that can be TRUE or FALSE'
Once you have declared a variable as a certain type, you cannot declare the variable under the same name again as a different type!
Forcing Variable Declarations
To force declaration of variables, use the following command:
Option Explicit
The Option Explicit statement has to be the first line in the module, before the first SUB. Generally, only arrays need to be declared explicitly. All other variables are declared according to the typedeclaration character, or  if omitted  as the default type Single.
Variable Types
LibreOffice Basic supports four variable classes:

Numeric variables can contain number values. Some variables are used to store large or small numbers, and others are used for floatingpoint or fractional numbers.

String variables contain character strings.

Boolean variables contain either the TRUE or the FALSE value.

Object variables can store objects of various types, like tables and documents within a document.
Integer Variables
Integer variables range from 32768 to 32767. If you assign a floatingpoint value to an integer variable, the decimal places are rounded to the next integer. Integer variables are rapidly calculated in procedures and are suitable for counter variables in loops. An integer variable only requires two bytes of memory. "%" is the typedeclaration character.
Dim Variable%
Dim Variable As Integer
Long Integer Variables
Long integer variables range from 2147483648 to 2147483647. If you assign a floatingpoint value to a long integer variable, the decimal places are rounded to the next integer. Long integer variables are rapidly calculated in procedures and are suitable for counter variables in loops for large values. A long integer variable requires four bytes of memory. "&" is the typedeclaration character.
Dim Variable&
Dim Variable As Long
Decimal Variables
Decimal variables can take positive or negative numbers or zero. Accuracy is up to 29 digits.
You can use plus (+) or minus () signs as prefixes for decimal numbers (with or without spaces).
If a decimal number is assigned to an integer variable, LibreOffice Basic rounds the figure up or down.
Single Variables
Single variables can take positive or negative values ranging from 3.402823 x 10E38 to 1.401298 x 10E45. Single variables are floatingpoint variables, in which the decimal precision decreases as the nondecimal part of the number increases. Single variables are suitable for mathematical calculations of average precision. Calculations require more time than for Integer variables, but are faster than calculations with Double variables. A Single variable requires 4 bytes of memory. The typedeclaration character is "!".
Dim Variable!
Dim Variable As Single
Double Variables
Double variables can take positive or negative values ranging from 1.79769313486232 x 10E308 to 4.94065645841247 x 10E324. Double variables are floatingpoint variables, in which the decimal precision decreases as the nondecimal part of the number increases. Double variables are suitable for precise calculations. Calculations require more time than for Single variables. A Double variable requires 8 bytes of memory. The typedeclaration character is "#".
Dim Variable#
Dim Variable As Double
Currency Variables
Currency variables are internally stored as 64bit numbers (8 Bytes) and displayed as a fixeddecimal number with 15 nondecimal and 4 decimal places. The values range from 922337203685477.5808 to +922337203685477.5807. Currency variables are used to calculate currency values with a high precision. The typedeclaration character is "@".
Dim Variable@
Dim Variable As Currency
String Variables
String variables can hold character strings with up to 65,535 characters. Each character is stored as the corresponding Unicode value. String variables are suitable for word processing within programs and for temporary storage of any nonprintable character up to a maximum length of 64 Kbytes. The memory required for storing string variables depends on the number of characters in the variable. The typedeclaration character is "$".
Dim Variable$
Dim Variable As String
Boolean Variables
Boolean variables store only one of two values: TRUE or FALSE. A number 0 evaluates to FALSE, every other value evaluates to TRUE.
Dim Variable As Boolean
Date Variables
Date variables can only contain dates and time values stored in an internal format. Values assigned to Date variables with Dateserial, Datevalue, Timeserial or Timevalue are automatically converted to the internal format. Datevariables are converted to normal numbers by using the Day, Month, Year or the Hour, Minute, Second function. The internal format enables a comparison of date/time values by calculating the difference between two numbers. These variables can only be declared with the key word Date.
Dim Variable As Date
Initial Variable Values
As soon as the variable has been declared, it is automatically set to the "Null" value. Note the following conventions:
Numeric variables are automatically assigned the value "0" as soon as they are declared.
Date variables are assigned the value 0 internally; equivalent to converting the value to "0" with the Day, Month, Year or the Hour, Minute, Second function.
String variables are assigned an emptystring ("") when they are declared.
Arrays
LibreOffice Basic knows one or multidimensional arrays, defined by a specified variable type. Arrays are suitable for editing lists and tables in programs. Individual elements of an array can be addressed through a numeric index.
Arrays must be declared with the Dim statement. There are several ways to define the index range of an array:
Dim Text$(20) '21 elements numbered from 0 to 20'
Dim Text$(5,4) '30 elements (a matrix of 6 x 5 elements)'
Dim Text$(5 To 25) '21 elements numbered from 5 to 25'
Dim Text$(15 To 5) '21 elements (including 0), numbered from 15 to 5'
The index range can include positive as well as negative numbers.
Constants
Constants have a fixed value. They are only defined once in the program and cannot be redefined later:
Const ConstName=Expression