Using functions in excel vba

This tutorial will teach you to create and use functions with and without parameters in VBA

VBA contains a large amount of built-in functions for you to use, but you are also able to write your own.   When you write code in VBA, you can write it in a Sub Procedure, or a Function Procedure. A Function Procedure is able to return a value to your code.  This is extremely useful if you want VBA to perform a task to return a result. VBA functions can also be called from inside Excel, just like Excel’s built-in Excel functions.

Creating a Function without Arguments

To create a function you need to define the function by giving the function a name. The function can then be defined as a data type indicating the type of data you want the function to return.

You may want to create a function that returns a static value each time it is called – a bit like a constant.

Function GetValue() As Integer
   GetValue = 50
End Function

If you were to run the function, the function would always return the value of 50.

You can also create functions that refer to objects in VBA but you need to use the Set Keyword to return the value from the function.

Function GetRange() as Range
  Set GetRange = Range("A1:G4")
End Function

If you were to use the above function in your VBA code, the function would always return the range of cells A1 to G4 in whichever sheet you are working in.

Calling a Function from a Sub Procedure

Once you create a function, you can call it from anywhere else in your code by using a Sub Procedure to call the function.

The value of 50 would always be returned.

You can also call the GetRange function from a Sub Procedure.

In the above example, the GetRange Function is called by the Sub Procedure to bold the cells in the range object.

Creating Functions

Single Argument

You can also assign a parameter or parameters to your function.  These parameters can be referred to as Arguments.

Function ConvertKilosToPounds (dblKilo as Double) as Double
   ConvertKiloToPounds = dblKilo*2.2
End Function

We can then call the above function from a Sub Procedure in order to work out how many pounds a specific amount of kilos are.

A function can be a called from multiple procedures within your VBA code if required.  This is very useful in that it stops you from having to write the same code over and over again.  It also enables you to divide long procedures into small manageable functions.

In the above example, we have 2 procedures – each of them are using the Function to calculate the pound value of the kilos passed to them in the dblKilo Argument of the function.

Multiple Arguments

You can create a Function with multiple arguments and pass the values to the Function by way of a Sub Procedure.

Function CalculateDayDiff(Date1 as Date, Date2 as Date) as Double
   CalculateDayDiff = Date2-Date1
End Function

We can then call the function to calculate the amount of days between 2 dates.

Optional Arguments

You can also pass Optional arguments to a Function.  In other words, sometimes you may need the argument, and sometimes you may not – depending on what code you are using the Function with .

Function CalculateDayDiff(Date1 as Date, Optional Date2 as Date) as Double
'check for second date and if not there, make Date2 equal to today's date.
   If Date2=0 then Date2 = Date
'calculate difference
   CalculateDayDiff = Date2-Date1 
End Function

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Default Argument Value

You can also set the default value of the Optional arguments when you are creating the function so that if the user omits the argument, the value that you have put as default will be used instead.

Function CalculateDayDiff(Date1 as Date, Optional Date2 as Date="06/02/2020") as Double 
'calculate difference 
   CalculateDayDiff = Date2-Date1 
End Function

ByVal and ByRef

When you pass values to a function, you can use the ByVal or ByRef keywords.  If you omit either of these, the ByRef is used as the default.

ByVal means that you are passing a copy of the variable to the function, whereas ByRef means you are referring to the original value of the variable.  When you pass a  copy of the variable (ByVal), the original value of the variable is NOT changed, but when you reference the variable, the original value of the variable is changed by the function.

Function GetValue(ByRef intA As Integer) As Integer
   intA = intA * 4
   GetValue = intA
End Function

In the function above, the ByRef could be omitted and the function would work the same way.

Function GetValue(intA As Integer) As Integer
   intA = intA * 4
   GetValue = intA
End Function

To call this function, we can run a sub-procedure.

Sub TestValues()
   Dim intVal As Integer
'populate the variable with the value 10
   intVal = 10
'run the GetValue function, and show the value in the immediate window
   Debug.Print GetValue(intVal)
'show the value of the intVal variable in the immediate window 
   Debug.Print  intVal
End Sub

Note that the debug windows show the value 40 both times.  When you pass the variable IntVal to the function – the value of 10 is passed to the function, and multiplied by 4.  Using the ByRef keyword (or omitting it altogether), will AMEND the value of the IntVal variable.   This is shown when you show first the result of the function in the immediate window (40), and then the value of the IntVal variable in the debug window (also 40).

If we do NOT want to change the value of the original variable, we have to use ByVal in the function.

Function GetValue(ByVal intA As Integer) As Integer
intA = intA * 4
GetValue = intA
End Function

Now if we call the function from a sub-procedure, the value of the variable IntVal will remain at 10.

Exit Function

If you create a function that tests for a certain condition, and once the condition is found to be true, you want return the value from the function, you may need to add an Exit Function statement in your Function in order to exit the function before you have run through all the code in that function.

Function FindNumber(strSearch As String) As Integer
   Dim i As Integer
'loop through each letter in the string
   For i = 1 To Len(strSearch)
   'if the letter is numeric, return the value to the function
      If IsNumeric(Mid(strSearch, i, 1)) Then
         FindNumber= Mid(strSearch, i, 1)
   'then exit the function
         Exit Function
      End If
   Next
   FindNumber= 0
End Function

The function above will loop through the string that is provided until it finds a number, and then return that number from the string.  It will only find the first number in the string as it will then Exit the function.

The function above can be called by a Sub routine such as the one below.

Sub CheckForNumber()
   Dim NumIs as Integer
'pass a text string to the find number function
   NumIs = FindNumber("Upper Floor, 8 Oak Lane, Texas")
'show the result in the immediate window
   Debug.Print NumIs
End Sub

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Using a Function from within an Excel Sheet

In addition to calling a function from your VBA code using a sub procedure, you can also call the function from within your Excel sheet.  The functions that you have created should by default appear in your function list in the User Defined section of the function list.

Click on the fx to show the Insert Function dialog box.

Select User Defined from the Category List

Select the function you require from the available User Defined Functions (UDF’s).

Alternatively, when you start writing your function in Excel, the function should appear in the drop down list of functions.

If you do not want the function to be available inside an Excel sheet, you need to put the Private word in front of the word Function when you create the function in your VBA code.

Private Function CalculateDayDiff(Date1 as Date, Date2 as Date) as Double 
   CalculateDayDiff = Date2-Date1 
End Function

It will now not appear in the drop down list showing the Excel functions available.

Interestingly enough, however, you can still use the function – it just will not appear in the list when looking for it!

If you have declared the second argument as Optional, you can omit it within the Excel sheet as well as within the VBA code.

You can also use the a function that you have created without arguments in your Excel sheet.

With VBA, you can create a custom Function (also called a User Defined Function) that can be used in the worksheets just like regular functions.

These are helpful when the existing Excel functions are not enough. In such cases, you can create your own custom User Defined Function (UDF) to cater to your specific needs.

In this tutorial, I’ll cover everything about creating and using custom functions in VBA.

If you’re interested in learning VBA the easy way, check out my Online Excel VBA Training.

What is a Function Procedure in VBA?

A Function procedure is a VBA code that performs calculations and returns a value (or an array of values).

Using a Function procedure, you can create a function that you can use in the worksheet (just like any regular Excel function such as SUM or VLOOKUP).

When you have created a Function procedure using VBA, you can use it in three ways:

1. As a formula in the worksheet, where it can take arguments as inputs and returns a value or an array of values.
2. As a part of your VBA subroutine code or another Function code.
3. In Conditional Formatting.

While there are already 450+ inbuilt Excel functions available in the worksheet, you may need a custom function if:

• The inbuilt functions can’t do what you want to get done. In this case, you can create a custom function based on your requirements.
• The inbuilt functions can get the work done but the formula is long and complicated. In this case, you can create a custom function that is easy to read and use.

Note that custom functions created using VBA can be significantly slower than the inbuilt functions. Hence, these are best suited for situations where you can’t get the result using the inbuilt functions.

Function Vs. Subroutine in VBA

A ‘Subroutine’ allows you to execute a set of code while a ‘Function’ returns a value (or an array of values).

To give you an example, if you have a list of numbers (both positive and negative), and you want to identify the negative numbers, here is what you can do with a function and a subroutine.

A subroutine can loop through each cell in the range and can highlight all the cells that have a negative value in it. In this case, the subroutine ends up changing the properties of the range object (by changing the color of the cells).

With a custom function, you can use it in a separate column and it can return a TRUE if the value in a cell is negative and FALSE if it’s positive. With a function, you can not change the object’s properties. This means that you can not change the color of the cell with a function itself (however, you can do it using conditional formatting with the custom function).

When you create a User Defined Function (UDF) using VBA, you can use that function in the worksheet just like any other function. I will cover more on this in the ‘Different Ways of Using a User Defined Function in Excel’ section.

Creating a Simple User Defined Function in VBA

Let me create a simple user-defined function in VBA and show you how it works.

The below code creates a function that will extract the numeric parts from an alphanumeric string.

Function GetNumeric(CellRef As String) as Long
Dim StringLength As Integer
StringLength = Len(CellRef)
For i = 1 To StringLength
If IsNumeric(Mid(CellRef, i, 1)) Then Result = Result & Mid(CellRef, i, 1)
Next i
GetNumeric = Result
End Function

When you have the above code in the module, you can use this function in the workbook.

Below is how this function – GetNumeric – can be used in Excel.

Now before I tell you how this function is created in VBA and how it works, there are a few things you should know:

• When you create a function in VBA, it becomes available in the entire workbook just like any other regular function.
• When you type the function name followed by the equal to sign, Excel will show you the name of the function in the list of matching functions. In the above example, when I entered =Get, Excel showed me a list that had my custom function.

I believe this is a good example when you can use VBA to create a simple-to-use function in Excel. You can do the same thing with a formula as well (as shown in this tutorial), but that becomes complicated and hard to understand. With this UDF, you only need to pass one argument and you get the result.

Anatomy of a User Defined Function in VBA

In the above section, I gave you the code and showed you how the UDF function works in a worksheet.

Now let’s deep dive and see how this function is created. You need to place the below code in a module in the VB Editor. I cover this topic in the section – ‘Where to put the VBA Code for a User-Defined Function’.

Function GetNumeric(CellRef As String) as Long
' This function extracts the numeric part from the string
Dim StringLength As Integer
StringLength = Len(CellRef)
For i = 1 To StringLength
If IsNumeric(Mid(CellRef, i, 1)) Then Result = Result & Mid(CellRef, i, 1)
Next i
GetNumeric = Result
End Function

The first line of the code starts with the word – Function.

This word tells VBA that our code is a function (and not a subroutine). The word Function is followed by the name of the function – GetNumeric. This is the name that we will be using in the worksheet to use this function.

• The name of the function cannot have spaces in it. Also, you can’t name a function if it clashes with the name of a cell reference. For example, you can not name the function ABC123 as it also refers to a cell in Excel worksheet.
• You shouldn’t give your function the same name as that of an existing function. If you do this, Excel would give preference to the in-built function.
• You can use an underscore if you want to separate words. For example, Get_Numeric is an acceptable name.

The function name is followed by some arguments in parenthesis. These are the arguments that our function would need from the user. These are just like the arguments that we need to supply to Excel’s inbuilt functions. For example in a COUNTIF function, there are two arguments (range and criteria)

Within the parenthesis, you need to specify the arguments.

In our example, there is only one argument – CellRef.

It’s also a good practice to specify what kind of argument the function expects. In this example, since we will be feeding the function a cell reference, we can specify the argument as a ‘Range’ type. If you don’t specify a data type, VBA would consider it to be a variant (which means you can use any data type).

If you have more than one arguments, you can specify those in the same parenthesis – separated by a comma. We will see later in this tutorial on how to use multiple arguments in a user-defined function.

Note that the function is specified as the ‘String’ data type. This would tell VBA that the result of the formula would be of the String data type.

While I can use a numeric data type here (such as Long or Double), doing that would limit the range of numbers it can return. If I have a 20 number long string that I need to extract from the overall string, declaring the function as a Long or Double would give an error (as the number would be out of its range). Hence I have kept the function output data type as String.

The second line of the code – the one in green that starts with an apostrophe – is a comment. When reading the code, VBA ignores this line. You can use this to add a description or a detail about the code.

The third line of the code declares a variable ‘StringLength’ as an Integer data type. This is the variable where we store the value of the length of the string that is being analyzed by the formula.

The fourth line declares the variable Result as a String data type. This is the variable where we will extract the numbers from the alphanumeric string.

The fifth line assigns the length of the string in the input argument to the ‘StringLength’ variable. Note that ‘CellRef’ refers to the argument that will be given by the user while using the formula in the worksheet (or using it in VBA – which we will see later in this tutorial).

Sixth, seventh, and eighth lines are the part of the For Next loop. The loop runs for as many times as many characters are there in the input argument. This number is given by the LEN function and is assigned to the ‘StringLength’ variable.

So the loop runs from ‘1 to Stringlength’.

Within the loop, the IF statement analyzes each character of the string and if it’s numeric, it adds that numeric character to the Result variable. It uses the MID function in VBA to do this.

The second last line of the code assigns the value of the result to the function. It’s this line of code that ensures that the function returns the ‘Result’ value back in the cell (from where it’s called).

The last line of the code is End Function. This is a mandatory line of code that tells VBA that the function code ends here.

The above code explains the different parts of a typical custom function created in VBA. In the following sections, we will deep dive into these elements and also see the different ways to execute the VBA function in Excel.

Arguments in a User Defined Function in VBA

In the above examples, where we created a user-defined function to get the numeric part from an alphanumeric string (GetNumeric), the function was designed to take one single argument.

In this section, I will cover how to create functions that take no argument to the ones that take multiple arguments (required as well as optional arguments).

Creating a Function in VBA without Any Arguments

In Excel worksheet, we have several functions that take no arguments (such as RAND, TODAY, NOW).

These functions are not dependent on any input arguments. For example, the TODAY function would return the current date and the RAND function would return a random number between 0 and 1.

You can create such similar function in VBA as well.

Below is the code that will give you the name of the file. It doesn’t take any arguments as the result it needs to return is not dependent on any argument.

Function WorkbookName() As String
WorkbookName = ThisWorkbook.Name
End Function

The above code specifies the function’s result as a String data type (as the result we want is the file name – which is a string).

This function assigns the value of  ‘ThisWorkbook.Name’ to the function, which is returned when the function is used in the worksheet.

If the file has been saved, it returns the name with the file extension, else it simply gives the name.

The above has one issue though.

If the file name changes, it wouldn’t automatically update. Normally a function refreshes whenever there is a change in the input arguments. But since there are no arguments in this function, the function doesn’t recalculate (even if you change the name of the workbook, close it and then reopen again).

If you want, you can force a recalculation by using the keyboard shortcut – Control + Alt + F9.

To make the formula recalculate whenever there is a change in the worksheet, you need to a line of code to it.

The below code makes the function recalculate whenever there is a change in the worksheet (just like other similar worksheet functions such as TODAY or RAND function).

Function WorkbookName() As String
Application.Volatile True
WorkbookName = ThisWorkbook.Name
End Function

Now, if you change the workbook name, this function would update whenever there is any change in the worksheet or when you reopen this workbook.

Creating a Function in VBA with One Argument

In one of the sections above, we have already seen how to create a function that takes only one argument (the GetNumeric function covered above).

Let’s create another simple function that takes only one argument.

Function created with the below code would convert the referenced text into uppercase. Now we already have a function for it in Excel, and this function is just to show you how it works. If you have to do this, it’s better to use the inbuilt UPPER function.

Function ConvertToUpperCase(CellRef As Range)
ConvertToUpperCase = UCase(CellRef)
End Function

This function uses the UCase function in VBA to change the value of the CellRef variable. It then assigns the value to the function ConvertToUpperCase.

Since this function takes an argument, we don’t need to use the Application.Volatile part here. As soon as the argument changes, the function would automatically update.

Creating a Function in VBA with Multiple Arguments

Just like worksheet functions, you can create functions in VBA that takes multiple arguments.

The below code would create a function that will extract the text before the specified delimiter. It takes two arguments – the cell reference that has the text string, and the delimiter.

Function GetDataBeforeDelimiter(CellRef As Range, Delim As String) as String
Dim Result As String
Dim DelimPosition As Integer
DelimPosition = InStr(1, CellRef, Delim, vbBinaryCompare) - 1
Result = Left(CellRef, DelimPosition)
GetDataBeforeDelimiter = Result
End Function

When you need to use more than one argument in a user-defined function, you can have all the arguments in the parenthesis, separated by a comma.

Note that for each argument, you can specify a data type. In the above example, ‘CellRef’ has been declared as a range datatype and ‘Delim’ has been declared as a String data type. If you don’t specify any data type, VBA considers these are a variant data type.

When you use the above function in the worksheet, you need to give the cell reference that has the text as the first argument and the delimiter character(s) in double quotes as the second argument.

It then checks for the position of the delimiter using the INSTR function in VBA. This position is then used to extract all the characters before the delimiter (using the LEFT function).

Finally, it assigns the result to the function.

This formula is far from perfect. For example, if you enter a delimiter that is not found in the text, it would give an error. Now you can use the IFERROR function in the worksheet to get rid of the errors, or you can use the below code that returns the entire text when it can’t find the delimiter.

Function GetDataBeforeDelimiter(CellRef As Range, Delim As String) as String
Dim Result As String
Dim DelimPosition As Integer
DelimPosition = InStr(1, CellRef, Delim, vbBinaryCompare) - 1
If DelimPosition < 0 Then DelimPosition = Len(CellRef)
Result = Left(CellRef, DelimPosition)
GetDataBeforeDelimiter = Result
End Function

We can further optimize this function.

If you enter the text (from which you want to extract the part before the delimiter) directly in the function, it would give you an error. Go ahead.. try it!

This happens as we have specified the ‘CellRef’ as a range data type.

Or, if you want the delimiter to be in a cell and use the cell reference instead of hard coding it in the formula, you can’t do that with the above code. It’s because the Delim has been declared as a string datatype.

If you want the function to have the flexibility to accept direct text input or cell references from the user, you need to remove the data type declaration. This would end up making the argument as a variant data type, which can take any type of argument and process it.

The below code would do this:

Function GetDataBeforeDelimiter(CellRef, Delim) As String
Dim Result As String
Dim DelimPosition As Integer
DelimPosition = InStr(1, CellRef, Delim, vbBinaryCompare) - 1
If DelimPosition < 0 Then DelimPosition = Len(CellRef)
Result = Left(CellRef, DelimPosition)
GetDataBeforeDelimiter = Result
End Function

Creating a Function in VBA with Optional Arguments

There are many functions in Excel where some of the arguments are optional.

For example, the legendary VLOOKUP function has 3 mandatory arguments and one optional argument.

An optional argument, as the name suggests, is optional to specify. If you don’t specify one of the mandatory arguments, your function is going to give you an error, but if you don’t specify the optional argument, your function would work.

But optional arguments are not useless. They allow you to choose from a range of options.

For example, in the VLOOKUP function, if you don’t specify the fourth argument, VLOOKUP does an approximate lookup and if you specify the last argument as FALSE (or 0), then it does an exact match.

Remember that the optional arguments must always come after all the required arguments. You can’t have optional arguments at the beginning.

Now let’s see how to create a function in VBA with optional arguments.

Function with Only an Optional Argument

As far as I know, there is no inbuilt function that takes optional arguments only (I can be wrong here, but I can’t think of any such function).

But we can create one with VBA.

Below is the code of the function that will give you the current date in the dd-mm-yyyy format if you don’t enter any argument (i.e. leave it blank), and in “dd mmmm, yyyy” format if you enter anything as the argument (i.e., anything so that the argument is not blank).

Function CurrDate(Optional fmt As Variant)
Dim Result
If IsMissing(fmt) Then
CurrDate = Format(Date, "dd-mm-yyyy")
Else
CurrDate = Format(Date, "dd mmmm, yyyy")
End If
End Function

Note that the above function uses ‘IsMissing’ to check whether the argument is missing or not. To use the IsMissing function, your optional argument must be of the variant data type.

The above function works no matter what you enter as the argument. In the code, we only check if the optional argument is supplied or not.

You can make this more robust by taking only specific values as arguments and showing an error in rest of the cases (as shown in the below code).

Function CurrDate(Optional fmt As Variant)
Dim Result
If IsMissing(fmt) Then
CurrDate = Format(Date, "dd-mm-yyyy")
ElseIf fmt = 1 Then
CurrDate = Format(Date, "dd mmmm, yyyy")
Else
CurrDate = CVErr(xlErrValue)
End If
End Function

The above code creates a function that shows the date in the “dd-mm-yyyy” format if no argument is supplied, and in “dd mmmm,yyyy” format when the argument is 1. It gives an error in all other cases.

Function with Required as well as Optional Arguments

We have already seen a code that extracts the numeric part from a string.

Now let’s have a look at a similar example that takes both required as well as optional arguments.

The below code creates a function that extracts the text part from a string. If the optional argument is TRUE, it gives the result in uppercase, and if the optional argument is FALSE or is omitted, it gives the result as is.

Function GetText(CellRef As Range, Optional TextCase = False) As String
Dim StringLength As Integer
Dim Result As String
StringLength = Len(CellRef)
For i = 1 To StringLength
If Not (IsNumeric(Mid(CellRef, i, 1))) Then Result = Result & Mid(CellRef, i, 1)
Next i
If TextCase = True Then Result = UCase(Result)
GetText = Result
End Function

Note that in the above code, we have initialized the value of ‘TextCase’ as False (look within the parenthesis in the first line).

By doing this, we have ensured that the optional argument starts with the default value, which is FALSE. If the user specifies the value as TRUE, the function returns the text in upper case, and if the user specifies the optional argument as FALSE or omits it, then the text returned is as is.

Creating a Function in VBA with an Array as the Argument

So far we have seen examples of creating a function with Optional/Required arguments – where these arguments were a single value.

You can also create a function that can take an array as the argument. In Excel worksheet functions, there are many functions that take array arguments, such as SUM, VLOOKUP, SUMIF, COUNTIF, etc.

Below is the code that creates a function that gives the sum of all the even numbers in the specified range of the cells.

Function AddEven(CellRef as Range)
 Dim Cell As Range
 For Each Cell In CellRef
 If IsNumeric(Cell.Value) Then
 If Cell.Value Mod 2 = 0 Then
 Result = Result + Cell.Value
 End If
 End If
 Next Cell
 AddEven = Result
 End Function

You can use this function in the worksheet and provide the range of cells that have the numbers as the argument. The function would return a single value – the sum of all the even numbers (as shown below).

In the above function, instead of a single value, we have supplied an array (A1:A10). For this to work, you need to make sure your data type of the argument can accept an array.

In the code above, I specified the argument CellRef as Range (which can take an array as the input). You can also use the variant data type here.

In the code, there is a For Each loop that goes through each cell and checks if it’s a number of not. If it isn’t, nothing happens and it moves to the next cell. If it’s a number, it checks if it’s even or not (by using the MOD function).

In the end, all the even numbers are added and teh sum is assigned back to the function.

Creating a Function with Indefinite Number of Arguments

While creating some functions in VBA, you may not know the exact number of arguments that a user wants to supply. So the need is to create a function that can accept as many arguments are supplied and use these to return the result.

An example of such worksheet function is the SUM function. You can supply multiple arguments to it (such as this):

=SUM(A1,A2:A4,B1:B20)

The above function would add the values in all these arguments. Also, note that these can be a single cell or an array of cells.

You can create such a function in VBA by having the last argument (or it could be the only argument) as optional. Also, this optional argument should be preceded by the keyword ‘ParamArray’.

‘ParamArray’ is a modifier that allows you to accept as many arguments as you want. Note that using the word ParamArray before an argument makes the argument optional. However, you don’t need to use the word Optional here.

Now let’s create a function that can accept an arbitrary number of arguments and would add all the numbers in the specified arguments:

Function AddArguments(ParamArray arglist() As Variant)
For Each arg In arglist
AddArguments = AddArguments + arg
Next arg
End Function

The above function can take any number of arguments and add these arguments to give the result.

Note that you can only use a single value, a cell reference, a boolean, or an expression as the argument. You can not supply an array as the argument. For example, if one of your arguments is D8:D10, this formula would give you an error.

If you want to be able to use both multi-cell arguments you need to use the below code:

Function AddArguments(ParamArray arglist() As Variant)
For Each arg In arglist
For Each Cell In arg
AddArguments = AddArguments + Cell
Next Cell
Next arg
End Function

Note that this formula works with multiple cells and array references, however, it can not process hardcoded values or expressions. You can create a more robust function by checking and treating these conditions, but that’s not the intent here.

The intent here is to show you how ParamArray works so you can allow an indefinite number of arguments in the function. In case you want a better function than the one created by the above code, use the SUM function in the worksheet.

Creating a Function that Returns an Array

So far we have seen functions that return a single value.

With VBA, you can create a function that returns a variant that can contain an entire array of values.

Array formulas are also available as inbuilt functions in Excel worksheets. If you’re familiar with array formulas in Excel, you would know that these are entered using Control + Shift + Enter (instead of just the Enter). You can read more about array formulas here. If you don’t know about array formulas, don’t worry, keep reading.

Let’s create a formula that returns an array of three numbers (1,2,3).

The below code would do this.

Function ThreeNumbers() As Variant
Dim NumberValue(1 To 3)
NumberValue(1) = 1
NumberValue(2) = 2
NumberValue(3) = 3
ThreeNumbers = NumberValue
End Function

In the above code, we have specified the ‘ThreeNumbers’ function as a variant. This allows it to hold an array of values.

The variable ‘NumberValue’ is declared as an array with 3 elements. It holds the three values and assigns it to the ‘ThreeNumbers’ function.

You can use this function in the worksheet by entering the function and hitting the Control + Shift + Enter key (hold the Control and the Shift keys and then press Enter).

When you do this, it will return 1 in the cell, but in reality, it holds all the three values. To check this, use the below formula:

=MAX(ThreeNumbers())

Use the above function with Control + Shift + Enter. You will notice that the result is now 3, as it is the largest values in the array returned by the Max function, which gets the three numbers as the result of our user-defined function – ThreeNumbers.

You can use the same technique to create a function that returns an array of Month Names as shown by the below code:

Function Months() As Variant
Dim MonthName(1 To 12)
MonthName(1) = "January"
MonthName(2) = "February"
MonthName(3) = "March"
MonthName(4) = "April"
MonthName(5) = "May"
MonthName(6) = "June"
MonthName(7) = "July"
MonthName(8) = "August"
MonthName(9) = "September"
MonthName(10) = "October"
MonthName(11) = "November"
MonthName(12) = "December"
Months = MonthName
End Function

Now when you enter the function =Months() in Excel worksheet and use Control + Shift + Enter, it will return the entire array of month names. Note that you see only January in the cell as that is the first value in the array. This does not mean that the array is only returning one value.

To show you the fact that it is returning all the values, do this – select the cell with the formula, go to the formula bar, select the entire formula and press F9. This will show you all the values that the function returns.

You can use this by using the below INDEX formula to get a list of all the month names in one go.

=INDEX(Months(),ROW())

Now if you have a lot of values, it’s not a good practice to assign these values one by one (as we have done above). Instead, you can use the Array function in VBA.

So the same code where we create the ‘Months’ function would become shorter as shown below:

Function Months() As Variant
Months = Array("January", "February", "March", "April", "May", "June", _
"July", "August", "September", "October", "November", "December")
End Function

The above function uses the Array function to assign the values directly to the function.

Note that all the functions created above return a horizontal array of values. This means that if you select 12 horizontal cells (let’s say A1:L1), and enter the =Months() formula in cell A1, it will give you all the month names.

But what if you want these values in a vertical range of cells.

You can do this by using the TRANSPOSE formula in the worksheet.

Simply select 12 vertical cells (contiguous), and enter the below formula.

Understanding the Scope of a User Defined Function in Excel

A function can have two scopes – Public or Private.

• A Public scope means that the function is available for all the sheets in the workbook as well as all the procedures (Sub and Function) across all modules in the workbook. This is useful when you want to call a function from a subroutine (we will see how this is done in the next section).
• A Private scope means that the function is available only in the module in which it exists. You can’t use it in other modules. You also won’t see it in the list of functions in the worksheet. For example, if your Function name is ‘Months()’, and you type function in Excel (after the = sign), it will not show you the function name. You can, however, still, use it if you enter the formula name.

If you don’t specify anything, the function is a Public function by default.

Below is a function that is a Private function:

Private Function WorkbookName() As String
WorkbookName = ThisWorkbook.Name
End Function

You can use this function in the subroutines and the procedures in the same modules, but can’t use it in other modules. This function would also not show up in the worksheet.

The below code would make this function Public. It will also show up in the worksheet.

Function WorkbookName() As String
WorkbookName = ThisWorkbook.Name
End Function

Different Ways of Using a User Defined Function in Excel

Once you have created a user-defined function in VBA, you can use it in many different ways.

Let’s first cover how to use the functions in the worksheet.

Using UDFs in Worksheets

We have already seen examples of using a function created in VBA in the worksheet.

All you need to do is enter the functions name, and it shows up in the intellisense.

Note that for the function to show up in the worksheet, it must be a Public function (as explained in the section above).

You can also use the Insert Function dialog box to insert the user defined function (using the steps below). This would work only for functions that are Public.

The above steps would insert the function in the worksheet. It also displays a Function Arguments dialog box that will give you details on the arguments and the result.

You can use a user defined function just like any other function in Excel. This also means that you can use it with other inbuilt Excel functions. For example. the below formula would give the name of the workbook in upper case:

=UPPER(WorkbookName())

Using User Defined Functions in VBA Procedures and Functions

When you have created a function, you can use it in other sub-procedures as well.

If the function is Public, it can be used in any procedure in the same or different module. If it’s Private, it can only be used in the same module.

Below is a function that returns the name of the workbook.

Function WorkbookName() As String 
WorkbookName = ThisWorkbook.Name 
End Function

The below procedure call the function and then display the name in a message box.

Sub ShowWorkbookName()
MsgBox WorkbookName
End Sub

You can also call a function from another function.

In the below codes, the first code returns the name of the workbook, and the second one returns the name in uppercase by calling the first function.

Function WorkbookName() As String
WorkbookName = ThisWorkbook.Name
End Function

Function WorkbookNameinUpper()
WorkbookNameinUpper = UCase(WorkbookName)
End Function

Calling a User Defined Function from Other Workbooks

If you have a function in a workbook, you can call this function in other workbooks as well.

There are multiple ways to do this:

1. Creating an Add-in
2. Saving function in the Personal Macro Workbook
3. Referencing the function from another workbook.

Creating an Add-in

By creating and installing an add-in, you will have the custom function in it available in all the workbooks.

Suppose you have created a custom function – ‘GetNumeric’ and you want it in all the workbooks. To do this, create a new workbook and have the function code in a module in this new workbook.

Now follow the steps below to save it as an add-in and then install it in Excel.

Now the add-in has been activated.

Now you can use the custom function in all the workbooks.

Saving the Function in Personal Macro Workbook

A Personal Macro Workbook is a hidden workbook in your system that opens whenever you open the Excel application.

It’s a place where you can store macro codes and then access these macros from any workbook. It’s a great place to store those macros that you want to use often.

By default, there is no personal macro workbook in your Excel. You need to create it by recording a macro and saving it in the Personal macro workbook.

You can find the detailed steps on how to create and save macros in the personal macro workbook here.

Referencing the function from another workbook

While the first two methods (creating an add-in and using personal macro workbook) would work in all situations, if you want to reference the function from another workbook, that workbook needs to be open.

Suppose you have a workbook with the name ‘Workbook with Formula’, and it has the function with the name ‘GetNumeric’.

To use this function in another workbook (while the Workbook with Formula is open), you can use the below formula:

=’Workbook with Formula’!GetNumeric(A1)

The above formula will use the user defined function in the Workbook with Formula file and give you the result.

Note that since the workbook name has spaces, you need to enclose it in single quotes.

Using Exit Function Statement VBA

If you want to exit a function while the code is running, you can do that by using the ‘Exit Function’ statement.

The below code would extract the first three numeric characters from an alphanumeric text string. As soon as it gets the three characters, the function ends and returns the result.

Function GetNumericFirstThree(CellRef As Range) As Long
Dim StringLength As Integer
StringLength = Len(CellRef)
For i = 1 To StringLength
If J = 3 Then Exit Function
If IsNumeric(Mid(CellRef, i, 1)) Then
J = J + 1
Result = Result & Mid(CellRef, i, 1)
GetNumericFirstThree = Result
End If
Next i
End Function

The above function checks for the number of characters that are numeric, and when it gets 3 numeric characters, it Exits the function in the next loop.

Debugging a User Defined Function

There are a few techniques you can use while debugging a user-defined function in VBA:

Debugging a Custom Function by Using the Message Box

Use MsgBox function to show a message box with a specific value.

The value you display can be based on what you want to test. For example, if you want to check if the code is getting executed or not, any message would work, and if you want to check whether the loops are working or not, you can display a specific value or the loop counter.

Debugging a Custom Function by  Setting the Breakpoint

Set a breakpoint to be able to go step through each line one at a time. To set a breakpoint, select the line where you want it and press F9, or click on the gray vertical area which is left to the code lines. Any of these methods would insert a breakpoint (you will see a red dot in the gray area).

Once you have set the breakpoint and you execute the function, it goes till the breakpoint line and then stops. Now you can step through the code using the F8 key. Pressing F8 once moves to the next line in the code.

Debugging a Custom Function by Using Debug.Print in the Code

You can use Debug.Print statement in your code to get the values of the specified variables/arguments in the immediate window.

For example, in the below code, I have used Debug.Print to get the value of two variables – ‘j’ and ‘Result’

Function GetNumericFirstThree(CellRef As Range) As Long
Dim StringLength As Integer
StringLength = Len(CellRef)
For i = 1 To StringLength
If J = 3 Then Exit Function
If IsNumeric(Mid(CellRef, i, 1)) Then
 J = J + 1
 Result = Result & Mid(CellRef, i, 1)
 Debug.Print J, Result
 GetNumericFirstThree = Result
End If
Next i
End Function

When this code is executed, it shows the following in the immediate window.

Excel Inbuilt Functions Vs. VBA User Defined Function

There are few strong benefits of using Excel in-built functions over custom functions created in VBA.

• Inbuilt functions are a lot faster than the VBA functions.
• When you create a report/dashboard using VBA functions, and you send it to a client/colleague, they wouldn’t have to worry about whether the macros are enabled or not. In some cases, clients/customers get scared by seeing a warning in the yellow bar (which simply asks them to enable macros).
• With inbuilt Excel functions, you don’t need to worry about file extensions. If you have macros or user-defined functions in the workbook, you need to save it in .xlsm.

While there are many strong reasons to use Excel in-built functions, in a few cases, you’re better off using a user-defined function.

• It’s better to use a user-defined function if your inbuilt formula is huge and complicated. This becomes even more relevant when you need someone else to update the formulas. For example, if you have a huge formula made up of many different functions, even changing a reference to a cell can be tedious and error-prone. Instead, you can create a custom function that only takes one or two arguments and does all the heavy lifting the backend.
• When you have to get something done that can not be done by Excel inbuilt functions. An example of this can be when you want to extract all the numeric characters from a string. In such cases, the benefit of using a user-defined function gar outweighs its negatives.

Where to put the VBA Code for a User-Defined Function

When creating a custom function, you need to put the code in the code window for the workbook in which you want the function.

Below are the steps to put the code for the ‘GetNumeric’ function in the workbook.

1. Go to the Developer tab.
2. Click on the Visual Basic option. This will open the VB editor in the backend.
3. In the Project Explorer pane in the VB Editor, right-click on any object for the workbook in which you want to insert the code. If you don’t see the Project Explorer go to the View tab and click on Project Explorer.
4. Go to Insert and click on Module. This will insert a module object for your workbook.
5. Copy and paste the code in the module window.

You May Also Like the Following Excel VBA Tutorials:

• Working with Cells and Ranges in Excel VBA.
• Working with Worksheets in Excel VBA.
• Working with Workbooks using VBA.
• How to use Loops in Excel VBA.
• Excel VBA Events – An Easy (and Complete) Guide
• Using IF Then Else Statements in VBA.
• How to Record a Macro in Excel.
• How to Run a Macro in Excel.
• How to Sort Data in Excel using VBA (A Step-by-Step Guide).
• Excel VBA InStr Function – Explained with Examples.

Home / VBA / VBA Worksheet Function (Use Excel Functions in a Macro)

Key Notes

• You can use the WorksheetFunction property to access worksheet functions to use in a macro.

How to use a Worksheet Functions in VBA while Writing a Macro

Use the following steps to use a worksheet function in VBA.

• First, specify the cell where you want to insert the values returned by the function.
  
• After that, use an equal sign (=) and type Application.WorksheetFunction (as you can already in the Excel application, you can only use WorksheetFunction).
  
• Next, you need to enter a dot (.), and the moment you do that, you’ll get a list of functions that you have in the worksheet.
  
• From here, let’s use the TextJoin function to join text from the cell A1 and B1. Just like that, you use a function in the worksheet; when you enter starting parentheses, it shows you the arguments that you need to specify in the cell.
  
• As you can see in the above screenshot, it shows you the argument that you need to specify, but not the name of the arguments. So, you need to know the arguments before using them. Here are the arguments that you need to use in TextJoin.
  
• Now, let’s enter arguments in the function.
  
  1. delimiter: “ “
  2. ignore_empty: True
  3. text1: Range(“A1”)
  4. text2: Range(“B1”)

Here’s the full code.

Sub MyMacro()

Range("A1") = _
Application.WorksheetFunction.TextJoin _
(" ", True, Range("A2"), Range("A3"))

End Sub

And when you run this macro:

There is a total of 387 worksheet functions that you can use in VBA. But there are a few functions (Example: LEFT) that are not available to use.

Reason? There are In-Built functions in VBA that you can use while writing a VBA code.

Let’s if you want to use a message box to get the value for a function. Lets you want to get the maximum value from the named range “myValues”.

The code would be:

Sub MyMacro()

MsgBox Prompt:=WorksheetFunction.Max(Range("myValues"))

End Sub

And here’s how you get a message box:

Application.WorksheetFunction vs. Application

There are two different ways to refer to a worksheet function. Below are the two different lines of code that perform the same activity.

Sub MyMacro()

MsgBox Prompt:= _
Application.WorksheetFunction.Max(Range("myValues"))

MsgBox Prompt:= _
Application.Max(Range("myValues"))

End Sub

But there’s a benefit to using the second method. It returns an error code instead of showing the error directly.

In This Chapter

Using functions to make your VBA expressions more powerful Using the VBA built-in functions Using Excel worksheet functions in your VBA code Writing custom functions
In previous chapters, I allude to the fact that you can use functions in your VBA expressions. I provide a full explanation in this chapter. Functions can make your VBA code perform some powerful feats, with little or no programming effort required. If you like that idea, this chapter’s for you.

What Is a Function?

All Excel users beyond rank beginners use worksheet functions in their formulas. The most common worksheet function is the SUM function, and you have hundreds of others at your disposal.
A function essentially performs a calculation and returns a single value. The SUM function, of course, returns the sum of a range of values. The same holds true for functions used in your VBA expressions: Each function does its thing and returns a single value.

The functions you use in VBA can come from three sources:

Built-in functions provided by VBA Worksheet functions provided by Excel
Custom functions that you (or someone else) write, using VBA
The rest of this chapter clarifies the differences and (I hope) convinces you of the value of using functions in your VBA code.

Using VBA Functions

VBA provides numerous built-in functions. Some of these functions take arguments and some do not.

VBA function examples

In this section, I present a few examples of using VBA functions in code. In many of these examples, I use the MsgBox function to display a value in a message box. Yes, MsgBox is a VBA function — a rather unusual one, but a function nonetheless. This useful function displays a message in a pop-up dialog box. For more details about the MsgBox function, see Chapter 15.
A workbook that contains all of the examples is available at this topic’s Web site.

Displaying the system date

The first example uses VBA’s Date function to display the current system date in a message box:

Notice that the Date function doesn’t use an argument. Unlike worksheet functions, a VBA function with no argument doesn’t require an empty set of parentheses. In fact, if you provide an empty set of parentheses, the VBE will remove them.
To get the system date and time, use the Now function instead of the Date function. Or to get only the time, use the Time function.

Finding a string length

The following procedure uses the VBA Len function, which returns the length of a string. The Len function takes one argument: the string. When you execute this procedure, the message box displays 11 because the argument has 11 characters.

Excel also has a function, which you can use in your worksheet formulas. The Excel version and the VBA function work the same.

Displaying the integer part of a number

The following procedure uses the Fix function, which returns the integer portion of a value — the value without any decimal digits:

In this case, the message box displays 123.
VBA has a similar function called Int. The difference between Int and Fix is how each deals with negative numbers.
Int returns the first negative integer that’s less than or equal to the argument.
Fix returns the first negative integer that’s greater than or equal to the argument.

Determining a file size

The following Sub procedure displays the size, in bytes, of the Excel executable file. It finds this value by using the FileLen function.

Notice that this routine hard codes the filename (that is, it explicitly states the path). Generally, this isn’t a good idea. The file might not be on the C drive, or the Excel folder may have a different name. The following statement shows a better approach:

Path is a property of the Application object. It simply returns the name of the folder in which the application (that is, Excel) is installed (without a trailing backslash).

Identifying the type of a selected object

The following procedure uses the Type Name function, which returns the type of the selected object (as a string):

This could be a Range, a ChartObject, a TextBox, or any other type of object that can be selected.
The TypeName function is very versatile. You can also use this function to determine the data type of a variable.
VBA functions that do more than return a value
A few VBA functions go above and beyond the call of duty. Rather than simply return a value, these functions have some useful side effects. Table 9-1 lists them.

Table 9-1	Functions with Useful Side Benefits
Function	What It Does
MsgBox	Displays a handy dialog box containing a message and buttons.
	The function returns a code that identifies which button the user
	clicks. See Chapter 15 for details.
InputBox	Displays a simple dialog box that asks the user for some input.
	The function returns whatever the user enters into the dialog
	box. I discuss this in Chapter 15.

Function	What It Does
Shell	Executes another program. The function returns the task ID
	(a unique identifier) of the other program (or an error if the
	function can’t start the other program).

Discovering VBA functions

How do you find out which functions VBA provides? Good question. The best source is the Excel Visual Basic Help system. I compiled a partial list of functions, which I share with you in Table 9-2. I omitted some of the more specialized or obscure functions.
For complete details on a particular function, type the function name into a VBA module, move the cursor anywhere in the text, and press F1.

Table 9-2	VBA’s Most Useful Built-in Functions
Function	What It Does
Abs	Returns a number’s absolute value
Array	Returns a variant containing an array
Asc	Converts the first character of a string to its ASCII value
Atn	Returns the arctangent of a number
Choose	Returns a value from a list of items
Chr	Converts an ANSI value to a string
Cos	Returns a number’s cosine
CurDir	Returns the current path
Date	Returns the current system date
DateAdd	Returns a date to which a specified time interval has been
	added — for example, one month from a particular date
DateDiff	Returns an integer showing the number of specified time intervals
	between two dates, for example the number of months between
	now and your birthday
DatePart	Returns an integer containing the specified part of a given
	date — for example, a date’s day of the year

Table 9-2 (continued)
Function	What It Does
DateSerial	Converts a date to a serial number
DateValue	Converts a string to a date
Day	Returns the day of the month from a date value
Dir	Returns the name of a file or directory that matches a pattern
Erl	Returns the line number that caused an error
Err	Returns the error number of an error condition
Error	Returns the error message that corresponds to an error number
Exp	Returns the base of the natural logarithm (e) raised to a power
FileLen	Returns the number of bytes in a file
Fix	Returns a number’s integer portion
Format	Displays an expression in a particular format
GetSetting	Returns a value from the Windows registry
Hex	Converts from decimal to hexadecimal
Hour	Returns the hours portion of a time
InputBox	Displays a box to prompt a user for input
InStr	Returns the position of a string within another string
Int	Returns the integer portion of a number
IPmt	Returns the interest payment for an annuity or loan
IsArray	Returns True if a variable is an array
IsDate	Returns True if an expression is a date
IsEmpty	Returns True if a variable has not been initialized
IsError	Returns True if an expression is an error value
IsMissing	Returns True if an optional argument was not passed to a
	procedure
IsNull	Returns True if an expression contains no valid data
IsNumeric	Returns True if an expression can be evaluated as a number

Function	What It Does
IsObject	Returns True if an expression references an OLE Automation object
LBound	Returns the smallest subscript for a dimension of an array
LCase	Returns a string converted to lowercase
Left	Returns a specified number of characters from the left of a string
Len	Returns the number of characters in a string
Log	Returns the natural logarithm of a number to base e
LTrim	Returns a copy of a string, with any leading spaces removed
Mid	Returns a specified number of characters from a string
Minute	Returns the minutes portion of a time value
Month	Returns the month from a date value
MsgBox	Displays a message box and (optionally) returns a value
Now	Returns the current system date and time
RGB	Returns a numeric RGB value representing a color
Right	Returns a specified number of characters from the right of a string
Rnd	Returns a random number between 0 and 1
RTrim	Returns a copy of a string, with any trailing spaces removed
Second	Returns the seconds portion of a time value
Sgn	Returns an integer that indicates a number’s sign
Shell	Runs an executable program
Sin	Returns a number’s sine
Space	Returns a string with a specified number of spaces
Sqr	Returns a number’s square root
Str	Returns a string representation of a number
StrComp	Returns a value indicating the result of a string comparison
String	Returns a repeating character or string
Tan	Returns a number’s tangent

Table 9-2 (continued)
Function	What It Does
Time	Returns the current system time
Timer	Returns the number of seconds since midnight
TimeSerial	Returns the time for a specified hour, minute, and second
TimeValue	Converts a string to a time serial number
Trim	Returns a string without leading or trailing spaces
TypeName	Returns a string that describes a variable’s data type
UBound	Returns the largest available subscript for an array’s dimension
UCase	Converts a string to uppercase
Val	Returns the numbers contained in a string
VarType	Returns a value indicating a variable’s subtype
Weekday	Returns a number representing a day of the week
Year	Returns the year from a date value

Using Worksheet Functions in VBA

Although VBA offers a decent assortment of built-in functions, you might not always find exactly what you need. Fortunately, you can also use most of Excel’s worksheet functions in your VBA procedures. The only worksheet functions that you cannot use are those that have an equivalent VBA function.
VBA makes Excel’s worksheet functions available through the Worksheet Function object, which is contained in the Application object. (Remember, the Application object is Excel.) Therefore, any statement that uses a worksheet function must use the Application. Worksheet Function qualifier. In other words, you must precede the function name with Application.Worksheet Function (with a dot separating the two). The following is an example:

You can omit the Application part of the expression because it’s assumed. You can also omit the Worksheet Function part of the expression; VBA will determine that you want to use an Excel worksheet function. But if you do so, then you must include the Application part. In other words, these three expressions all work exactly the same:

My personal preference is to use the Worksheet Function part just to make it perfectly clear that the code is using an Excel function.

Worksheet function examples

In this section, I demonstrate how to use worksheet functions in your VBA expressions.

Finding the maximum value in a range

Here’s an example showing how to use the MAX worksheet function in a VBA procedure. This procedure displays the maximum value in the range named Number List on the active worksheet:

You can use the MIN function to get the smallest value in a range. And, as you might expect, you can use other worksheet functions in a similar manner. For example, you can use the LARGE function to determine the kth-largest value in a range. The following expression demonstrates this:

Notice that the LARGE function uses two arguments; the second argument represents the kth part — 2 in this case (the second-largest value).

Calculating a mortgage payment

The next example uses the PMT worksheet function to calculate a mortgage payment. I use three variables to store the data that’s passed to the Pmt function as arguments. A message box displays the calculated payment.

As the following statement shows, you can also insert the values directly as the function arguments:

However, using variables to store the parameters makes the code easier to read and modify, if necessary.

Using a lookup function

The following example uses the simple lookup table shown in Figure 9-1. Range A1:B13 is named Price List.

You can download this workbook from the topic’s Web site.

Figure 9-1:
The range, named Price List, contains prices for parts.

The procedure starts this way:

1. VBA’s InputBox function asks the user for a part number.
Figure 9-2 shows the Microsoft Excel dialog box that displays when this statement is executed.
2. This statement assigns the part number the user enters for the PartNum variable.
3. The next statement activates the Prices worksheet, just in case it’s not already the active sheet.

Figure 9-2:
Use the InputBox function to get the user’s input.
4. The code uses the VLOOKUP function to find the part number in the table.
Notice that the arguments you use in this statement are the same as those you would use with the function in a worksheet formula. This statement assigns the result of the function to the Price variable.
5. The code displays the price for the part via the MsgBox function.
This procedure doesn’t have any error handling, and it fails miserably if you enter a nonexistent part number. (Try it.) Add some error-handling statements for a more robust procedure. I discuss error handling in Chapter 12.

Entering worksheet functions

You can’t use the Excel Paste Function dialog box to insert a worksheet function into a VBA module. Instead, enter such functions the old-fashioned way: by hand. However, you can use the Paste Function dialog box to identify the function you want to use and find out about its arguments.
1. Activate a worksheet.
2. Choose Insert Function as you normally would.
3. Figure out how the function works.
4. Type the function and its arguments into your module.
Follow these steps to display the VBE’s Auto List Members option, which displays a drop-down list of all worksheet functions:
1. Type Application.Worksheet Function, followed by a period.
2. If this feature isn’t working, choose the VBE’s Tools Options command.
3. Click the Editor tab.
4. Place a check mark next to Auto List Members.

More about Using Worksheet Functions

Newcomers to VBA often confuse VBA’s built-in functions and Excel’s workbook functions. A good rule to remember is that VBA doesn’t try to reinvent the wheel. For the most part, VBA doesn’t duplicate Excel worksheet functions.
Bottom line? If you need to use a function, first determine whether VBA has something that meets your needs. If not, check out the worksheet functions. If all else fails, you may be able to write a custom function by using VBA.
The Worksheet Function object contains the worksheet functions available to VBA procedures. To see a list of these functions, you can use the Object Browser as shown in Figure 9-3. Follow these steps to display a complete list of worksheet functions available in VBA:
1. In the VBE, press F2.
The Object Browser appears.
2. In the Project/Library drop-down list (the one in the upper-left corner of the Object Browser), select Excel.
3. In the list labeled Classes, select Worksheet Function.
The Members of list shows all the worksheet functions you can use in your code.
For most worksheet functions that are unavailable as methods of the Application object, you can use an equivalent VBA built-in operator or function. For example, the MOD worksheet function is unavailable in
the Worksheet Function object because VBA has an equivalent, built-in Mod operator. This is by design — a VBA operator works faster than an Excel function in a VBA module.

Figure 9-3:
Use the Object Browser to show the worksheet function available in VBA.

Using Custom Functions

I’ve covered VBA functions and Excel worksheet functions. The third category of functions you can use in your VBA procedures is custom functions. A custom function is one you develop yourself using (what else?) VBA. To use a custom function, you must define it in the workbook in which you use it.

Here’s an example of defining a simple Function procedure and then using it in a VBA Sub procedure:

The custom function Multiply Two has two arguments. The Show Result Sub procedure uses this Function procedure by passing two arguments to it (in parentheses). The Show Result procedure then displays a message box showing the value returned by the Multiply Two function.
The Multiply Two function is fairly useless. It’s much more efficient to perform the multiplication in the Show Result Sub procedure. I include it simply to give you an idea of how a Sub procedure can make use of a custom function.
You can use custom functions also in your worksheet formulas. For example, if Multiply Two is defined in your workbook, you can write a formula such as this one:

This formula returns the product of the values in cells A1 and A2.
Custom worksheet functions is an important (and very useful) topic. So important (and useful) that I devote an entire chapter to it. See Chapter 21.