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==Implicit Variable Declaration ==

Basic languages are designed to be easy to use. As a result, {{OOo}} Basic enables the creation of a variable through simple usage and without an explicit declaration. In other words, a variable exists from the moment that you include it in your code. Depending on the variables that are already present, the following example declares up to three new variables:

 a = b + c

Declaring variables implicitly is not good programming practice because it can result in the inadvertent introduction of a new variable through, for example, a typing error. Instead of producing an error message, the interpreter initializes the typing error as a new variable with a value of 0. It can be very difficult to locate errors of this kind in your code.

==Explicit Variable Declaration ==

To prevent errors caused by an implicit declaration of variables, {{OOo}} Basic provides a switch called:

<source lang="oobas">
Option Explicit
</source>

This must be listed in the first program line of each module and ensures that an error message is issued if one of the variables used is not declared. The <tt>Option Explicit</tt> switch should be included in all Basic modules.

In its simplest form, the command for an explicit declaration of a variable is as follows:

<source lang="oobas">
Dim MyVar
</source>

This example declares a variable with the name <tt>MyVar</tt> and the type <tt>variant</tt>. A variant is a universal variable that can record all conceivable values, including strings, whole numbers, floating point figures, and Boolean values. Here are a few examples of Variant variables:

<source lang="oobas">
MyVar = "Hello World"      ' Assignment of a string
MyVar = 1                  ' Assignment of a whole number
MyVar = 1.0                ' Assignment of a floating point number
MyVar = True               ' Assignment of a Boolean value
</source>

The variables declared in the previous example can even be used for different variable types in the same program. Although this provides considerable flexibility, it is best to restrict a variable to one variable type. When {{OOo}} Basic encounters an incorrectly defined variable type in a particular context, an error message is generated.

Use the following style when you make a type-bound variable declaration:

<source lang="oobas">
Dim MyVar As Integer   ' Declaration of a variable of the integer type
</source>

The variable is declared as an integer type and can record whole number values. You can also use the following style to declare an integer type variable:

<source lang="oobas">
Dim MyVar%          ' Declaration of a variable of the integer type
</source>

The Dim instruction can record several variable declarations:

<source lang="oobas">
Dim MyVar1, MyVar2
</source>

If you want to assign the variables to a permanent type, you must make separate assignments for each variable:

<source lang="oobas">
Dim MyVar1 As Integer, MyVar2 As Integer
</source>

If you do not declare the type for a variable, {{OOo}} Basic assigns the variable a variant type. For example, in the following variable declaration, <tt>MyVar1</tt> becomes a variant and <tt>MyVar2</tt> becomes an integer:

<source lang="oobas">
Dim MyVar1, MyVar2 As Integer
</source>

The following sections list the variable types that are available in {{OOo}} Basic and describe how they can be used and declared.
 
{{PDL1}}