Visual Basic 2005 Guide
Working With Variables

What Is A Variable?

When your program runs, the data that it uses is stored in main memory (RAM). The programmer makes up a name (a variable) to identify where this information is stored. The value we give to a variable can vary depending on how we write our program.

Data Types

When we use variables, we need to think about the type of data that we want to store. In Visual Basic, we will need to use the following data types.

Data TypeWhat Is StoredPossible ValuesStorage
IntegerWhole Numbers-2000 million to +2000 million (approx)4
LongWhole NumbersVery small to Very Large8
SingleDecimal NumbersVery small to Very Large4
StringOne or more charactersAny characters1 per char
DateDates and timeDates and times8
BooleanTrue or falseTrue, False2

You will notice that a different data types require different amounts of storage space. This is because Visual Basic stores each data type in a different way. There are more data types, check the help file if you think you need to use a different type.

Declaring A Variable

To declare a variable you must tell Visual Basic what you want to call it and what type of data you want to store. You use the keywords Dim and As to declare a variable.

For example.

Dim intNumber As Integer
Dim sglTotal As Single
Dim dtPayment As Date

Try to use meaningful names for your variables. The variable declarations above use a prefix of 2 or 3 letters to show the data type. You cannot use spaces in the names of variables.

Using Variables In Your Code

1. Start a new project and get to the code window by clicking on View Code on the menu.

2. You should see the following lines in the code window,

Public Class Form1

End Class

3. Type the following variable declarations.

Dim intFirstNumber As Integer
Dim intSecondNumber As Integer
Dim intTotal as Integer

4. Return to the form and double click on the Form to get to the form's Load event code. Type in the following lines.

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
   intFirstNumber = InputBox("Enter your first number")
   intSecondNumber = InputBox("Enter your second number")
   intTotal = intFirstNumber + intSecondNumber
   MsgBox("The total is " & intTotal)
End Sub

5. Save your work and test your program. Remember that there is a limit on the size of the Integer data type.

In addition to showing how integer variables can be declared and used in a program, this program introduces you to the most basic forms of input and output in Visual Basic. The Inputbox() and MsgBox() functions will come in useful in lots of programs.

Variable Scope

The variables that you declare in your programs have what is called scope. A variable that you declare at the top of the form (like in the program above) is called a global variable. It can be used in any of the subroutines of the program without losing its value. Any variables that you declare within a subroutine only retain their values within that subroutine. If you refer to them in another subroutine, an error is generated.