SQL Select

Hi,

I was trying few queries on SQL server, i just gave the below query and i was baffled with the result it gave.

Query : Select '1' + 1

Result = 2

I was expecting the sql server to throw an error while i try to add varchar 1 ('1') and the integer 1 (1), instead it added both the numbers and returned the result as 2.
Can anyone guide me on my the select query added those 2 numbers and why it did not throw an error.

Thanks in advance,
Rajeeva