Lesson 2 Variables, Constants and Data Types

2.1 The Definition of Variables

In general, variables are something that varies , just like the files in your cabinet or the mailboxes where their content always change from time to time. In Excel 2010 VBA , variables are areas allocated by the computer memory to hold data.

2.2 Rules in Naming Variables

Like the mailboxes, each variable must be given a name. The following are the rules when naming a variable :

• It must not exceed 40 characters
• No space is allowed
• It must contain only letters, numbers and underscore characters
• It must not begin with a number, must always begin with a letter
• Period is not permitted

Examples of valid and invalid variable names are displayed in Table 2.1

2.3 Data Types

Excel 2010 VBA data types can be grossly divided into two types, the numeric data types and non-numeric data types. They are classified below:

2.3.1 Numeric Data Types

Numeric data types are types of data that consist of numbers, which can be computed mathematically with various standard operators such as addition, subtraction, multiplication, division and more. Examples of numeric data types are examination marks, height, weight, number of students in a class, share values, the price of goods, monthly bills, fees and others.

2.3.2 Non-Numeric Data Types

Non-numeric data types are data that cannot be manipulated mathematically using standard arithmetic operators. The non-numeric data comprises text or string data types, the Date data types, the Boolean data types that store only two values (true or false), Object data type and Variant data type .They are summarized in Table 2.3

2.3.3 Testing Data Types

We can test out the type of data held by a variant by using the function VarType. To run the test, enter the Excel 2010 VBA code IDE and create a subroutine such as below:

Sub TestVarType()
 MyVariable1 = "Francis"
 MsgBox VarType(MyVariable1)
 MyVariable1 = 1234
 MsgBox VarType(MyVariable1)
End Sub

2.4 Declaration of variables

In Excel VBA 2010, we need to declare the variables before using them by assigning names and data types.

2.4.1 Implicit Declaration

We can use a variable without openly(explicitly) declare it if we assign an initial value to it. For example,

MyFirstName="John"

Excel 2010 VBA will automatically create a variable MyFirstName as a variant, and it will hold the data as John. This type of declaration is called implicit declaration.

2.4.2 Explicit Declaration

Implicit declaration of the variable often leads to errors in writing code, therefore, it is better to declare a variable explicitly. It is declared using the Dim statement as follows:

Dim VariableName As DataType

If you want to declare more variables, you can declare them in separate lines or you may also combine more in one line, separating each variable with a comma, as follows:

Dim VariableName1 As DataType1, VariableName2 As DataType2, VariableName3 As DataType3

Example 2.1

Dim password As String
Dim yourName As String
Dim firstnum As Integer
Dim secondnum As Integer
Dim total As Integer
Dim doDate As Date
Dim password As String,  yourName As String, firstnum As Integer

For fixed-length string, you can use the statement to declare the variable:

Dim VariableName as String * n

where n defines the number of characters the string can hold. Example:

Dim yourName as String * 10

yourName can hold no more than 10 Characters.

2.4.3 Scope of Declaration

Other than using the Dim keyword to declare the data, you can also use other keywords to declare the data. These keywords indicate the scope of the declaration, they are private ,static and public,as follows:

Private VariableName as Datatype
Static VariableName as Datatype
Public VariableName as Datatype

The Private declares a local variable or a variable that is local to a procedure or module in Excel VBA 2010.

The Static keyword declares a variable that can be used multiple times, even after a procedure has been terminated. Most variables created inside a procedure are discarded by Visual Basic when the procedure is finished, static keyword preserves the value of a variable even after the procedure is terminated.

The Public keyword declares a global variable, which means it can be used by all the procedures and modules of the whole program.

2.5 Constants

Constants are different from variables in the sense that their values do not change during the running of the program. In Excel 2010 VBA , the statement to declare a constant is

Const Constant Name As Data Type = Value

Examples:

Const Pi As Single=3.142
Const Temp As Double=37
Const Score As Single=100