When declaring variables, you usually use a Dim statement. A declaration statement can be placed within a procedure to create a procedure-level variable. Or it may be placed at the top of a module, in the Declarations section, to create a module-level variable.
The following example creates the variable
and specifies the String data type
If this statement appears within a procedure, the variable
can be used only in that procedure. If the statement appears in the Declarations section of the module, the variable
is available to all procedures within the module, but not to procedures in other modules in the project
. To make this variable available to all procedures in the project, precede it with the Public
statement, as in the following example:
For information about naming your variables, see "Visual Basic Naming Rules" in Visual Basic Help.
Variables can be declared as one of the following data types: Boolean, Byte, Integer, Long, Currency, Single, Double, Date, String (for variable-length strings), String * length (for fixed-length strings), Object, or Variant. If you do not specify a data type, the Variant data type is assigned by default. You can also create a user-defined type using the Type statement. For more information on data types, see "Data Type Summary" in Visual Basic Help.
You can declare several variables in one statement. To specify a data type, you must include the data type for each variable. In the following statement, the variables
are declared as type Integer
Dim intX As Integer, intY As Integer, intZ As Integer
In the following statement,
are declared as type Variant
is declared as type Integer
Dim intX, intY, intZ As Integer
You don't have to supply the variable's data type in the declaration statement. If you omit the data type, the variable will be of type Variant.
Using the Public Statement
You can use the Public statement to declare public module-level variables.
Public variables can be used in any procedures in the project. If a public variable is declared in a standard module or a class module, it can also be used in any projects that reference the project where the public variable is declared.
Using the Private Statement
You can use the Private statement to declare private module-level variables.
Private variables can be used only by procedures in the same module.
|When used at the module level, the Dim statement is equivalent to the Private statement. You might want to use the Private statement to make your code easier to read and interpret.
Using the Static Statement
When you use the Static statement instead of a Dim statement, the declared variable will retain its value between calls.
Using the Option Explicit Statement
You can implicitly declare a variable in Visual Basic simply by using it in an assignment statement. All variables that are implicitly declared are of type Variant. Variables of type Variant require more memory resources than most other variables. Your application will be more efficient if you declare variables explicitly and with a specific data type. Explicitly declaring all variables reduces the incidence of naming-conflict errors and spelling mistakes.
If you don't want Visual Basic to make implicit declarations, you can place the Option Explicit statement in a module before any procedures. This statement requires you to explicitly declare all variables within the module. If a module includes the Option Explicit statement, a compile-time error will occur when Visual Basic encounters a variable name that has not been previously declared, or that has been spelled incorrectly.
You can set an option in your Visual Basic programming environment to automatically include the Option Explicit statement in all new modules. See your application's documentation for help on how to change Visual Basic environment options. Note that this option does not change existing code you have written.
|You must explicitly declare fixed arrays and dynamic arrays.
Declaring an Object Variable for Automation
When you use one application to control another application's objects, you should set a reference to the other application's type library. Once you set a reference, you can declare object variables according to their most specific type. For example, if you are in Microsoft Word when you set a reference to the Microsoft Excel type library, you can declare a variable of type Worksheet from within Microsoft Word to represent a Microsoft Excel Worksheet object.
If you are using another application to control Microsoft Access objects, in most cases, you can declare object variables according to their most specific type. You can also use the New keyword to create a new instance of an object automatically. However, you may have to indicate that it is a Microsoft Access object. For example, when you declare an object variable to represent a Microsoft Access form from within Microsoft Visual Basic, you must distinguish the Microsoft Access Form object from a Visual Basic Form object. Include the name of the type library in the variable declaration, as in the following example:
Dim frmOrders As New Access.Form
Some applications don't recognize individual Microsoft Access object types. Even if you set a reference to the Microsoft Access type library from these applications, you must declare all Microsoft Access object variables as type Object. Nor can you use the New keyword to create a new instance of the object. The following example shows how to declare a variable to represent an instance of the Microsoft Access Application object from an application that doesn't recognize Microsoft Access object types. The application then creates an instance of the Application object.
Dim appAccess As Object
Set appAccess = CreateObject("Access.Application")
To determine which syntax an application supports, see the application's documentation.