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Chapter 5. Variables, Data Types, and Constants

Chapter 5. Variables, Data Types, and Constants

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Dim dt As Date

dt = #1/2/97#



A symbolic constant (also sometimes referred to simply as a constant) is a name for a literal

constant.

To define or declare a symbolic constant in a program, we use the Const keyword, as in:

Const InvoicePath = "d:\Invoices\"



In this case, Excel will replace every instance of InvoicePath in our code with the string

"d:\Invoices\". Thus, InvoicePath is a constant, since it never changes value, but it is not

a literal constant, since it is not used as written.

The virtue of using symbolic constants is that, if we decide later to change "d:\Invoices\" to

"d:\OldInvoices\", we only need to change the definition of InvoicePath to:

Const InvoicePath = "d:\OldInvoices\"



rather than searching through the entire program for every occurrence of the phrase

"d:\Invoices\".



It is generally good programming practice to declare any symbolic constants at the beginning of

the procedure in which they are used (or in the Declarations section of a code module). This

improves readability and makes housekeeping simpler.

In addition to the symbolic constants that you can define using the Const statement, VBA has a

large number of built-in symbolic constants (about 700), whose names begin with the lowercase

letters vb. Excel VBA adds additional symbolic constants (1266 of them) that begin with the

letters xl. We will encounter many of these constants throughout the book.

Among the most commonly used VBA constants are vbCrLf, which is equivalent to a carriage

return followed by a line feed, and vbTab, which is equivalent to the tab character.



5.3.1 Enums

Microsoft has recently introduced a structure into VBA to categorize the plethora of symbolic

constants. This structure is called an enum , which is short for enumeration. A list of enums can be

obtained using my Object Model Browser software. For instance, among Excel's 152 enums, there

is one for the fill type used by the AutoFill method, defined as follows:

Enum XlAutoFillType

xlFillDefault = 0

xlFillCopy = 1

xlFillSeries = 2

xlFillFormats = 3

xlFillValues = 4

xlFillDays = 5

xlFillWeekdays = 6

xlFillMonths = 7

xlFillYears = 8

xlLinearTrend = 9

xlGrowthTrend = 10

End Enum



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(The Excel documentation incorrectly refers to this enum as XlFillType.) Note that enum

names begin with the letters Xl (with an uppercase X ).

Thus, the following line of code will autofill the first seven cells in the first row of the active sheet

with the days of the week, assuming that the first cell contains the word Monday:

ActiveSheet.Range("A1").AutoFill ActiveSheet.Range("A1:G1"),

xlFillDays



This is far more readable than:

ActiveSheet.Range("A1").AutoFill ActiveSheet.Range("A1:G1"), 5



Note that this enum is built in, so we do not need to add it to our programs in order to use these

symbolic constants. (We can create our own enums, but this is generally not necessary in Excel

VBA programming, since Excel has done such a good job of this for us.)

As another example, the built-in enum for the constant values that can be returned when the user

dismisses a message box (by clicking on a button) is:

Enum VbMsgBoxResult

vbOK = 1

vbCancel = 2

vbAbort = 3

vbRetry = 4

vbIgnore = 5

vbYes = 6

vbNo = 7

End Enum



For instance, when the user hits the OK button on a dialog box (assuming it has one), VBA returns

the value vbOK. Certainly, it is a lot easier to remember that VBA will return the symbolic

constant vbOK than to remember that it will return the constant 1. (We will discuss how to get and

use this return value later.)

VBA also defines some symbolic constants that are used to set the types of buttons that will

appear on a message box. These are contained in the following enum (which includes some

additional constants not shown):

Enum VbMsgBoxStyle

vbOKOnly = 0

vbOKCancel = 1

vbAbortRetryIgnore = 2

vbYesNoCancel = 3

vbYesNo = 4

vbRetryCancel = 5

End Enum



To illustrate, consider the following code:

If MsgBox("Proceed?", vbOKCancel) = vbOK Then

' place code to execute when user hits OK button

Else

' place code to execute when user hits any other button

End If



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In the first line, the code MsgBox("Proceed?", vbOKCancel) causes Excel to display a

message box with an OK button and a Cancel button and the message "Proceed?", as shown in

Figure 5-1.

Figure 5-1. Example message box



If the user clicks the OK button, Excel will return the constant value vbOK; otherwise it will return

the value vbCancel. Thus, the If statement in the first line will distinguish between the two

responses. (We will discuss the If statement in detail in Chapter 8. Here, we are interested in the

role of symbolic constants.)

In case you are not yet convinced of the value of symbolic constants, consider the following enum

for color constants:

Enum ColorConstants

vbBlack = 0

vbBlue = 16711680

vbMagenta = 16711935

vbCyan = 16776960

vbWhite = 16777215

vbRed = 255

vbGreen = 65280

vbYellow = 65535

End Enum



Consider which you'd rather type, this:

ATextBox.ForeColor = vbBlue



or this:

ATextBox.ForeColor = 16711680



Need I say more?



5.4 Variables and Data Types

A variable can be thought of as a memory location that can hold values of a specific type. The

value in a variable may change during the life of the program—hence the name variable.

In VBA, each variable has a specific data type, which indicates which type of data it may hold.

For instance, a variable that holds text strings has a String data type and is called a string variable.

A variable that holds integers (whole numbers) has an Integer data type and is called an integer



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variable. For reference, Table 5-1 shows the complete set of VBA data types, along with the

amount of memory that they consume and their range of values. We will discuss a few of the more

commonly used data types in a moment.

Table 5-1. VBA Data Types

Type

Size in Memory

Range of Values

Byte

1 byte

0 to 255

Boolean

2 bytes

True or False

Integer

2 bytes

-32,768 to 32,767

Long (long integer) 4 bytes

-2,147,483,648 to 2,147,483,647

Single(single4 bytes

Approximately -3.4E38 to 3.4E38

precision real)

Double(double8 bytes

Approximately -1.8E308 to 4.9E324

precision real)

Currency(scaled

Approximately -922,337,203,685,477.5808

8 bytes

integer)

to 922,337,203,685,477.5807

Date

8 bytes

1/1/100 to 12/31/9999

Object

4 bytes

Any Object reference.

Variable length:10 bytes +

Variable length: <= about 2 billion (65,400

String

string length;Fixed length:

for Win 3.1) Fixed length: up to 65,400

string length

16 bytes for numbers22 bytes Number: same as DoubleString: same as

Variant

+ string length

String

User-defined

Varies



5.4.1 Variable Declaration

To declare a variable means to define its data type. Variables are declared with the Dim keyword

(or with the keywords Private and Public, which we will discuss later in this chapter). Here

are some examples:

Dim

Dim

Dim

Dim

Dim

Dim

Dim



Name As String

Holiday As Date

Age As Integer

Height As Single

Money As Currency

wbk As Workbook

ch As Chart



The general syntax of a variable declaration is:

Dim VariableName As DataType



If a particular variable is used without first declaring it, or if it is declared without mentioning a

data type, as in:

Dim Age



then VBA will treat the variable as having type Variant. As we can see from Table 5-1, this is

generally a waste of memory, since variants require more memory than most other types of

variables.



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For instance, an integer variable requires 2 bytes, whereas a variant that holds the same integer

requires 16 bytes, which is a waste of 14 bytes. It is not uncommon to have hundreds or even

thousands of variables in a complex program, and so the memory waste could be significant. For

this reason, it is a good idea to declare all variables.

Perhaps more importantly, much more overhead is involved in maintaining a Variant than its

corresponding String or Integer, for example. This in turn means that using Variants typically

results in worse performance than using an equivalent set of explicit data types.

We can place more than one declaration on a line to save space. For instance, the following line

declares three variables:

Dim Age As Integer, Name As String, Money As Currency



Note, however, that a declaration such as:

Dim Age, Height, Weight As Integer



is legal, but Age and Height are declared as Variants, not Integers. In other words, we must

specify the type for each variable explicitly.

It is also possible to tell VBA the type of the variable by appending a special character to the

variable name. In particular, VBA allows the type-declaration suffixes shown in Table 5-2. (I

personally dislike these suffixes, but they do save space.)



Suffix

%

&

!

#

@

$



Table 5-2. Type-Declaration Suffixes

Type

integer

long

single

double

currency

string



For instance, the following line declares a variable called Name$ of type String:

Dim Name$



We can then write:

Name$ = "Donna"



Finally, let us note that although Excel allows variable and constant declarations to be placed

anywhere within a procedure (before the item is used, that is), it is generally good programming

practice to place all such declarations at the beginning of the procedure. This improves code

readability and makes housekeeping much simpler.



5.4.2 The Importance of Explicit Variable Declaration

We have said that using the Variant data type generally wastes memory and often results in poorer

performance. There is an additional, even more important reason to declare all variables explicitly.

This has to do with making typing errors, which we all do from time to time. In particular, if we

accidentally misspell a variable name, VBA will think we mean to create a new variable!



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To illustrate how dangerous this can be, consider the NewBook procedure in Example 5-1, whose

purpose is to take the first open workbook, change its contents, ask the user for a name under

which to save the changed workbook, and then save the workbook under the new name.

Example 5-1. A Procedure with a Typo

Sub NewBook()

Dim Wbk As Workbook

Dim WbkName As String

' Get first open workbook

Set Wbk = Workbooks(1)

' Get the workbook name

WbkName = Wbk.Name

' Code to change the contents of the workbook

' goes here . . .

' Ask user for new name for document

WkbName = InputBox("Enter name for workbook " & WbkName)

' Save the workbook

Wbk.SaveAs WbkName

End Sub



Observe that there is a typographical error (the b and k are transposed) in the following line:

WkbName = InputBox("Enter name for workbook " & WbkName)



Since the variable WkbName is not declared, Excel will treat it as a new variable and give it the

Variant data type. Moreover, VBA will assume that we want the new filename to be assigned to

the variable WkbName, and will save the changed document under its original name, which is

stored in WbkName. Thus, we will lose the original workbook when it is inadvertently overwritten

without warning!

5.4.2.1 Option Explicit

To avoid the problem described in the previous example, we need a way to make Excel refuse to

run a program if it contains any variables that we have not explicitly declared. This is done simply

by placing the line:

Option Explicit



in the Declarations section of each code module. Since it is easy to forget to do this, VBA

provides an option called "Require Variable Declaration" in its Options dialog box. When this

option is selected, VBA automatically inserts the Option Explicit line for us. Therefore, I

strongly recommend that you enable this option.

Now let us briefly discuss some of the data types in Table 5-1.



5.4.3 Numeric Data Types

The numeric data types include Integer, Long, Single, Double, and Currency. A long is also

sometimes referred to as a long integer.



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5.4.4 Boolean Data Type

A Boolean variable is a variable that takes on one of two values: True or False. This is a very

useful data type that was only recently introduced into VBA. Prior to its introduction, VBA

recognized 0 as False and any nonzero value as True, and you may still see this usage in older

code.



5.4.5 String Data Type

A string is a sequence of characters. (An empty string has no characters, however.) A string may

contain ordinary text characters (letters, digits, and punctuation) as well as special control

characters such as vbCrLf (carriage return/line feed characters) or vbTab (tab character). As we

have seen, a string constant is enclosed within quotation marks. The empty string is denoted by a

pair of adjacent quotation marks, as in:

EmptyString = ""



There are two types of string variables in VBA: fixed-length and variable-length. A fixed-length

string variable is declared as follows:

Dim FixedStringVarName As String * StringLen



For instance, the following statement declares a fixed-length string of length 10 characters:

Dim sName As String * 10



Observe that the following code, which concatenates two strings:

Dim s As String * 10

s = "test"

Debug.Print s & "/"



and produces the output:

test



/



This shows that the content of a fixed-length string is padded with spaces in order to reach the

correct length.

A variable-length string variable is a variable that can hold strings of varying lengths (at different

times, of course). Variable-length string variables are declared simply as:

Dim VariableStringVarName As String



As an example, the code:

Dim s As String

s = "test"

Debug.Print s & "/"

s = "another test"

Debug.Print s & "/"



produces the output:



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