Copy Formula From Previous Cell To Next Cell When I Enter Something

I want to copy formula from previous row to next cell when i enter something in perticular cell.
i.e

--Colomn A --- Colomn B -- --------Colomn C
1 01-09-07 ----- John ----------=vlookup(b2,$s$1:$t$10,2,false)
2 01-09-07 ----- Smith -------- =vlookup(b3,$s$1:$t$10,2,false)
3
4
5

Now if i enter date in cell A3 then cell C3 should be automatically filled/copy formula as celll C2. and so on......
then if i enter data to A4 then cell C4 should be automatically filled/copy formula from cell C3.

I have also attached example file.