Declaring Variables in Visual Basic

Before you use a variable you must declare it. To declare a variable you can use the Dim statement.

Dim intNumber As Integer

Dim decInterestRate As Decimal

Rules for naming variables in Visual Basic

Must be unique within scope
Must begin with a letter or the underscore _ character
May not contain embedded spaces or many special characters (. , “ - $ # * and others). The underscore _ is a valid character.
May not be a reserved word

In addition

Use upper and lower case with purpose. Once a variable is declared you do not have to be concerned with upper/lower case. The editor recognizes words that are the same except for case and makes them all the same for you. (use of upper and lower case differ between languages)
It is good programming practice in any language to use naming conventions (rules, standards) to name your variables. In Visual Basic the naming conventions include using a prefix that identifies the variable’s data type.

intNumber	The prefix int would signify an integer variable
decHours	The prefix dec would signify an Decimal variable, use sng for Single and use dbl for Double
strName	The prefix str would signify a string variable
blnYearEnd	The prefix bln would signify a Boolean variable

By default it is REQUIRED to declare variables before you use them. If you do not declare variables an error --- Name 'xxx' is not declared will be reported. However it is not syntactically required that you indicate a data type. In this class you must declare the data type when you declare the variable.

It is not a violation of the rules of the language to declare more than one variable on the same line

Dim intNumber As Integer, decAmount As Decimal, strName As String

But it is not advised. We will declare only one variable per line

Dim intnumber As Integer

Dim decAmount As Decimal

Dim strName As String

Variables may be declared in the declarations section of the Form or within the procedure in which they will be used. A variable declared at Form/Class level is “known” to every procedure in the Form. That means all procedures may use variables declared at “Form level”. A variable declared at the “procedure level” is “known” only to that procedure and can only be referenced by statements within that procedure.

In Visual Basic all variables are assigned an initial value automatically.

All numeric variables have an initial value of 0 (zero)
All string variables are empty

This is NOT the case in all computer languages. C, C++, and Java do NOT automatically initialize variables.

Since the need for variables arise throughout the programming process you will typically work back and forth between the variables declarations and the instructions during the creation of a program, declaring new variables as the need arises.