Using Excel Vba Global Variables Effectively

When it comes to writing efficient and effective VBA code in Excel, the use of global variables can play a significant role. Global variables are variables that are declared outside of a procedure or function and are accessible from any part of the code. In this article, we will explore the best practices for using global variables in Excel VBA, including their benefits, declaration, and usage.

Benefits of Using Global Variables

Before we dive into the details of using global variables, let's first explore their benefits. Global variables can be useful in the following situations:

When you need to share data between multiple procedures or functions.
When you want to avoid passing variables as arguments to procedures or functions.
When you want to make your code more readable and maintainable.

Example of Using Global Variables

Suppose we have a VBA code that performs different operations on a worksheet, such as formatting cells, inserting charts, and printing the worksheet. We can declare global variables to store the worksheet object, chart object, and other settings that need to be shared across different procedures.

Public ws As Worksheet
Publiccht As Chart
Public printSettings As Boolean

Sub InitializeVariables()
    Set ws = ThisWorkbook.Worksheets("Sheet1")
    Set cht = ws.ChartObjects(1).Chart
    printSettings = True
End Sub

Sub FormatCells()
    ws.Cells.Font.Name = "Calibri"
    ws.Cells.Font.Size = 12
End Sub

Sub InsertChart()
    cht.ChartType = xlColumnClustered
    cht.SeriesCollection.NewSeries
    cht.SeriesCollection(1).Name = "Series 1"
End Sub

Sub PrintWorksheet()
    If printSettings Then
        ws.PrintOut
    End If
End Sub

Declaring Global Variables

To declare a global variable in VBA, you need to use the Public keyword followed by the variable name, data type, and scope. The scope can be either Module or Global.

Module-level scope: The variable is accessible only within the module where it is declared.
Global scope: The variable is accessible from any part of the code.

Here are some examples of declaring global variables:

Public myVariable As Integer ' Global scope
Public Const PI As Double = 3.14159 ' Global scope
Private myPrivateVariable As String ' Module-level scope

Best Practices for Declaring Global Variables

When declaring global variables, follow these best practices:

Use meaningful and descriptive names for your variables.
Avoid using ambiguous names that can be confused with built-in VBA variables or functions.
Use the Public keyword to declare global variables.
Use the Private keyword to declare module-level variables.
Avoid using the Dim statement to declare global variables, as it can lead to confusion.

Using Global Variables Effectively

To use global variables effectively, follow these guidelines:

Minimize the use of global variables: While global variables can be useful, they can also lead to tight coupling between different parts of the code. Try to minimize their use by passing variables as arguments to procedures or functions.
Use global variables for constants: Global variables can be useful for storing constants that need to be shared across different parts of the code.
Avoid using global variables for large data structures: Global variables can be slow and inefficient for large data structures. Instead, consider using arrays, collections, or custom objects.
Use global variables for utility functions: Global variables can be useful for storing utility functions that need to be shared across different parts of the code.

Example of Using Global Variables for Utility Functions

Suppose we have a VBA code that needs to perform different utility functions, such as formatting dates, converting numbers to strings, and getting the current user name. We can declare global variables to store these utility functions.

Public Function FormatDate(dateValue As Date) As String
    FormatDate = Format(dateValue, "yyyy-mm-dd")
End Function

Public Function ConvertNumberToString(numValue As Integer) As String
    ConvertNumberToString = CStr(numValue)
End Function

Public Function GetCurrentUserName() As String
    GetCurrentUserName = Environ$("USERNAME")
End Function

Conclusion

In conclusion, global variables can be a powerful tool in Excel VBA programming. By following the best practices outlined in this article, you can use global variables effectively to make your code more readable, maintainable, and efficient. Remember to minimize the use of global variables, use them for constants and utility functions, and avoid using them for large data structures.