Excel VBA - Passing a Dynamic Range to a Function - excel

Question

I created a function in Excel VBA:
Function codeList(Criteria As String, LookupRange As Range, ValueRange As Range, delimiter As String)
It works great when I pass hard coded ranges to it like this:
ActiveCell.FormulaR1C1 = "=codelist(RC[2],R2C4:R84C4,R2C3:R84C3,"","")"
I would like the rows to be dynamic, so instead of saying C2:C84 or D2:D84 I would like to make the C84 / D84 vary based on the number of columns that have data.
I tried to compute the last row and concatenate the ranges to make them dynamic when I call the function, but I get a compile syntax error :
Dim lastRow As Long
lastRow = Range("C" & Rows.Count).End(xlUp).Row
ActiveCell.FormulaR1C1 = "=codelist(RC[2],"R2C4:R" & lastrow &"C4", "R2C3:R" & lastrow & "C3"),"","")"
Any suggestions on how to make this work?

Answer 1

When you want to include double quotes inside a string, you have to use two double quotes to escape them.
ActiveCell.FormulaR1C1 = "=codelist(RC[2],R2C4:R" & lastRow & "C4, R2C3:R" & lastRow & "C3,"""")"
The four double quotes near the end convert to two double quotes (the empty string your looking for).
This way is longer, but I tend to use offsets in formulas. I find it easier to read than trying to determine where the strings begin and end
Const DBLQTE As String = """"""
ActiveCell.FormulaR1C1 = "=codelist(RC[2]," & _
Range("D2").Resize(lastRow - 1).Address(, , xlR1C1) & _
"," & _
Range("C2").Resize(lastRow - 1).Address(, , xlR1C1) & _
"," & _
DBLQTE & _
")"
Update
For a comma delimeter
ActiveCell.FormulaR1C1 = "=codelist(RC[2],R2C4:R" & lastRow & "C4, R2C3:R" & lastRow & "C3,"","")"
and
Const COMMA As String = ""","""
ActiveCell.FormulaR1C1 = "=codelist(RC[2]," & _
Range("D2").Resize(lastRow - 1).Address(, , xlR1C1) & _
"," & _
Range("C2").Resize(lastRow - 1).Address(, , xlR1C1) & _
"," & _
COMMA & _
")"

Answer 2

Qualify the parent worksheet and resize according to the column's populated limit. Resize every associated range that needs to be the same size.
Function codeList(Criteria As String, LookupRange As Range, ValueRange As Range, delimiter As String)
with LookupRange.parent
set LookupRange = .range(LookupRange.cells(1), .cells(.rows.count, LookupRange.cells(LookupRange.cells.count).column).end(xlup))
set ValueRange = ValueRange.cells(1).resize(LookupRange.rows.count, LookupRange.columns.count)
end with
'all the rest of the code
end function
Never use ActiveSheet or ActiveCell in a worksheet's UDF. The originating cell where the formula is in is the Application.Caller.