Excel's Formula - sisman

Chapter 25: VBA Custom Function Examples 711
Function SIMPLESUM(ParamArray arglist() As Variant) As Double
Dim arg as Variant
For Each arg In arglist
SIMPLESUM = SIMPLESUM + arg
Next arg
End Function
The following formula returns the sum of the single-cell arguments:
=SIMPLESUM(A1,A5,12)
The most serious limitation of the SIMPLESUM function is that it does not handle multicell
ranges. This improved version does:
Function SIMPLESUM(ParamArray arglist() As Variant) As Double
Dim arg as Variant
Dim cell as Range
For Each arg In arglist
If TypeName(arg) = “Range” Then
For Each cell In arg
SIMPLESUM = SIMPLESUM + cell.Value
Next cell
Else
SIMPLESUM = SIMPLESUM + arg
End If
Next arg
End Function
This function checks each entry in the Arglist array. If the entry is a range, then the code uses
a For Each-Next loop to sum the cells in the range.
Even this improved version is certainly no substitute for the Excel SUM function. Try it by using
various types of arguments, and you’ll see that it fails unless each argument is a value or a range
reference. Also, if an argument consists of an entire column, you’ll find that the function is very
slow because it evaluates every cell — even the empty ones.
Emulating the Excel SUM function
This section presents a Function procedure called MYSUM. Unlike the SIMPLESUM function
listed in the previous section, MYSUM emulates the Excel SUM function perfectly.
Before you look at the code for the MYSUM function, take a minute to think about the Excel SUM
function. This very versatile function can have any number of arguments (even missing arguments),