VBScript Tutorials - Herong's Tutorial Notes
Dr. Herong Yang, Version 4.01

Variables - Declaration and Assignment

Part:   1   2 

VB Script Tutorials - Herong's Tutorial Notes © Dr. Herong Yang

Data Types and Literals

Variables

Logic Operations

String Operations

Conditional Statements

Arrays

Loop Statements

Functions and Subroutines

Built-in Functions

Variable Inspection

... Table of Contents

This chapter describes:

  • Variable Declaration
  • Assigning Values to Variables
  • Variable Default Values

Variable Declaration

Like many other programming languages, Visual Basic (VB) uses variables to reserve memory to store data and to name that memory location.

A variable must be declared with a name and a specific data type. Here are the rules on variable declaration:

1. Explicit Declaration - A variable is declared with the "Dim" statement in the following syntax:

   Dim variable_name As data_type

where "variable_name" is a text label to identify this variable; and "data_type" is one of the data type key words: "Byte", "Integer", "Long", "Single", "Double", "Currency", "String", "Boolean", "Date", and "Variant".

If a variable is declared without "As" and the data type key word, it will be assumed with the "Variant" data type.

2. Implicit Declaration - A variable name is used on the left side of an assignment statement without being declared previously. The data type of an implicitly declared variable is "Variant".

Visual Basic Scripts Restriction: Visual Basic scripts used in IE or IIS only supports "Variant" type of variables. So you:

  • Can use implicit variable declaration.
  • Can use explicit variable declaration without "As" and data type keywords.
  • Can NOT use explicit variable declaration with "As" and data type keywords.

Just in case you want to know, "Dim" stands for "Dimension".

Assigning Values to Variables

Variables can be assigned with new values with the assignment statement in the following syntax:

   variable_name = data_value

where "data_value" a data literal or an expression. We will look at expressions in details in other parts of this book.

When assigning a new value to a variable, the data type of the new value must match the data type of the variable.

Since we can not declare specific variable types in VB scripts, I wrote the following VB code module in Microsoft Access:

Sub Main()
'  VariableType.bas
'  Copyright (c) 2006 by Dr. Herong Yang. http://www.herongyang.com/

   Dim c As Byte
   Dim i As Integer
   Dim l As Long
   Dim f As Single
   Dim d As Double
   Dim y As Currency
   Dim s As String
   Dim b As Boolean
   Dim t As Date
   Dim v As Variant

(Continued on next part...)

Part:   1   2 

Dr. Herong Yang, updated in 2006
VBScript Tutorials - Herong's Tutorial Notes - Variables - Declaration and Assignment