Transact SQL :: Conversion Failed - Int Is Incompatible With Date

I tried a simple declaration

declare @fromdate date
declare @todate date
set @fromdate='2011-12-01'
set @todate='2012-11-31'
print @fromdate
print @todate

Got the error as "Conversion failed when converting date and/or time from character string." then i tried as below

declare @fromdate date
declare @todate date
set @fromdate=12-01-2011
set @todate=11-31-2012
print @fromdate
print @todate

this time got the error as ''
Msg 206, Level 16, State 2, Line 3
Operand type clash: int is incompatible with date
Msg 206, Level 16, State 2, Line 4
Operand type clash: int is incompatible with date".