orclz> conn hr/hr
Connected.
orclz> create or replace procedure upd_man(dep_id employees.department_id%type)
  2  as
  3  emp employees_employee_id%type;
  4  begin
  5  select employee_id into emp from employees
  6  where department_id = dep_id
  7  and
  8  salary = (select max(salary) from employees where department_id = dep_id);
  9  update departments set manager_id = emp where department_id = dep_id;
 10  end;
 11  /

Warning: Procedure created with compilation errors.

orclz> sho err
Errors for PROCEDURE UPD_MAN:

LINE/COL ERROR
-------- -----------------------------------------------------------------
3/5      PL/SQL: Item ignored
3/5      PLS-00201: identifier 'EMPLOYEES_EMPLOYEE_ID' must be declared
5/1      PL/SQL: SQL Statement ignored
5/25     PLS-00320: the declaration of the type of this expression is
         incomplete or malformed

5/29     PL/SQL: ORA-00904: : invalid identifier
9/1      PL/SQL: SQL Statement ignored
9/37     PL/SQL: ORA-00904: "EMP": invalid identifier
9/37     PLS-00320: the declaration of the type of this expression is
         incomplete or malformed

orclz>

CREATE OR REPLACE PROCEDURE UPD_MAN(DEP_ID EMPLOYEES.DEPARTMENT_ID%TYPE)
AS

    emp employees.employee_id%TYPE;

BEGIN

  BEGIN
  
     SELECT employee_id 
     INTO   emp 
     FROM   employees
     WHERE  department_id = dep_id
     AND    salary = (  SELECT    MAX(salary) 
                        FROM      employees 
                        WHERE     department_id = dep_id
                     );
                     
  EXCEPTION
  WHEN no_data_found then 
  
     NULL;
  END;
  
     UPDATE departments 
     SET    manager_id = emp 
     WHERE  department_id = dep_id;
 
 COMMIT;
 
END;

EXCEPTION
  WHEN no_data_found then 
  
     NULL;
  END;

BEGIN

  UPDATE departments 
  SET    manager_id = (SELECT employee_id 
                       FROM   employees
                       WHERE  department_id = dep_id
                       AND    salary = (SELECT    MAX(salary) 
                                        FROM      employees 
                                        WHERE     department_id = dep_id
                                       )
                      )
  WHERE  department_id = dep_id;
  
  IF sql%rowcount = 0 THEN
  
    raise_application_error(-20001, 'Dept '||dep_id||' does not exist.');
    
  END IF;
  
END;