Excel Macro edited w/VB, Add cells in columns

I have this loop that works:

While Range("A" & i) <> ""
Range("C" & i).Select
Range("C" & i) = DealerID
Range("D" & i).Select
Range("D" & i) = "N"
i = i + 1
Wend

This does not:

While Range("A" & j) <> ""
Range("J" & j).Select
Range("K" & j).Select
Range("L" & j).Select
Range("L" & j) = Range("J" & j) + Range("K" & j)
j = j + 1
Wend

How do I subscript "J" and "K" and add them to "L"