I created one tablespace.After creating tablspace I dropped the datafile on operating system.I was supposed to
 execute  drop tablespace including contents and datafiles.
Somehow I dropped the datafile prior to give this command.
Now I am not able to drop tablespace.
Can you give any idea how to drop the tablespace as I have to recreate tablespace
with same name.

I created one tablespace.
After creating tablspace I dropped the datafile on operating system.
I was supposed to execute  drop tablespace including contents and datafiles.
Somehow I dropped the datafile prior to give this command.
Now I am not able to drop tablespace.
Can you give any idea how to drop the tablespace 
as I have to recreate tablespace with same name.

SQL> insert into t2 values (t2_s.nextval, x1) returning id into :x2;
insert into t2 values (t2_s.nextval, x1) returning id into :x2
*
ERROR at line 1:
ORA-00984: column not allowed here

I had given the following command to create tablespace:-
create tablespace sitecom_d01 datafile
'/data3/oradata/sc/sitecom_d01.dbf' reuse
autoexend on extent management local;
Then I deleted sitecom_d01.dbf from operating system.
Now I am trying to drop the tablespace and it is giving
me the following error:-

ORA-01116: error in opening database file 12
ORA-01110: data file 12: '/data3/oradata/sc/SITECOM_D01.dbf'
ORA-27041: unable to open file
SVR4 Error: 2: No such file or directory
Additional information: 3
How can I drop the tablespace now

alter database datafile 'datafile path' offline drop
drop tablespace tablespace_name including contents.