I'm trying to insert the formula shown in CODE 2 below into cells C3:C13.
C3:C13 is a named range that always will be constantly growing, so my
function
InsertFormula() in CODE 1 should handle the range expanding dilema.

My question is syntax with the formula. CODE 2 shows the formula needed in
C3. However, when my function loops to the C4 cell, the formula being
inserted needs to change from using A3 cell to the A4 cell, and so on until
the function fills my range will the formula.

Can someone help me modify my InsertFormula() function to insert the formula
in each cell while incrementing the relative cell reference?

CODE 1:

Sub InsertFormula()

Dim c As Range

Set c = ActiveSheet.Range("C3")

Do While c.Offset(0, -2).Value < ""
c.Value = xxxxxx ' Should be my formula
Set c = c.Offset(1, 0)
Loop

End Sub

CODE 2:

=IF(ISNA(VLOOKUP(A3,DataRange,1,FALSE)),"",A3)