Connected to Personal Oracle Database 10g Release 10.2.0.3.0 
Connected as kassa@RUSTEST

SQL> 
SQL> create or replace function get_count_of_accounts(bankID number, contrID number)
  2  return number
  3  as
  4  countAc number;
  5  begin
  6  select count(*) into countAc from accounts where bank_id=bankID and contr_id=contrID and sysdate>=dayfrom and sysdate<=dayto;
  7  return countAc;
  8  end;
  9  /

Warning: Function created with compilation errors


SQL> show errors;
Errors for FUNCTION KASSA.GET_COUNT_OF_ACCOUNTS:
LINE/COL ERROR
-------- -----------------------------------------------
6/35     PL/SQL: ORA-00942: table or view does not exist
6/1      PL/SQL: SQL Statement ignored

SQL> 
SQL> create or replace function get_count_of_accounts(bankID number, contrID number)
  2  return number
  3  as
  4  countAc number;
  5  begin
  6  select count(*) into countAc from dual;
  7  return countAc;
  8  end;
  9  /

Function created


SQL> select get_count_of_accounts(0, 0) from dual;

GET_COUNT_OF_ACCOUNTS(0,0)
--------------------------
                         1

SQL>