How to insert column in sql server dynamically using stored procedures? : M trying this query bt its not working.

CREATE PROCEDURE USP_UPDATEUSERS_0 @COLUMNNAME NVARCHAR(30),@DATATYPE NVARCHAR(30) AS ALTER TABLE HC_USER_MAIN ADD COLUMNNAME=@COLUMNNAME DATATYPE=@DATATYPE

its showing error:
Msg 102, Level 15, State 1, Procedure USP_UPDATEUSERS_0, Line 1
Incorrect syntax near '='.