add columns if not exists in oracle

DECLARE 
    v_col_exists number := 0;
begin
select count(1) into v_col_exists from user_tab_cols where TABLE_NAME = UPPER('<table_nane>');

if(v_col_exists = 0) then 
execute immediate '';
else 
dbms_output.put_line('already there');
end if;
end;
/