Help needed

Hi to all

am new in this forum & new to plsql. i wish to become a plsql developer.i wish you people help me for this.
Today i installed Oracle 11gR2 and sql Developer.i write a simple pgm.the pgm was successfully complied but i cant see the output in results.
Is there any mistakes in my code Or is there any changes in developer tool to see the results.

declare
row_count number(5);
begin
update employees
set salary= salary+100 where employee_id >150;
if sql%notfound then
dbms_output.put_line('No records updated');
elsif sql%found then
row_count := sql%rowcount;
dbms_output.put_line('number of updated employees are'||row_count);
end if;
exception
when no_data_found then
dbms_output.put_line('No records in this range');
end;


Thanks in Advance
Pravi