Oracle function compilation error PLS-00103 (Encountered the symbol "SELECT" ...)

Question

I receive the following error when I compile this function:

Compilation errors for PROCEDURE INV.USP_MSC_MODIFICA_ESTADO

Error: PLS-00103: Encountered the symbol "SELECT" when expecting one of the following:( - + case mod new not null <an identifier>
<a double-quoted delimited-identifier> <a bind variable>
 continue avg count current exists max min prior sql stddev
sum variance execute forall merge time timestamp interval
date <a string literal with character set specification>
<a number> <a single-quoted SQL string> pipe
<an alternatively-quoted string literal with character set specification>
<an alternat    Line: 14    Text: IF SELECT TRUNC((SYSDATE) -TO_DATE(@FCH_GRABACION, 'DD/MM/YYYY HH24:MI:SS')) From DUAL=1 THEN

CREATE OR REPLACE PROCEDURE "USP_MSC_MODIFICA_ESTADO" AS
  BEGIN
    DECLARE
      CURSOR reservar IS
      SELECT
        id_reserva,
        fch_grabacion 
       FROM tb_msc_reserva
      WHERE to_date(to_char(fch_grabacion, 'dd/mm/yyyy')) = to_date(to_char(SYSDATE, 'dd/mm/yyyy')) - 1;
      id_reserva    VARCHAR2(50);
      fch_grabacion DATE;
    BEGIN
      OPEN reservar;
      FETCH reservar INTO id_reserva, fch_grabacion;

      IF SELECT TRUNC((SYSDATE) - TO_DATE(@fch_grabacion, 'DD/MM/YYYY HH24:MI:SS')) FROM dual=1 THEN

      UPDATE inv.tb_msc_reserva t
      SET t.flg_estado = 'C'
      WHERE id_reserva = @id_reserva;
      COMMIT;
    END if;
    WHILE (@@fetch_status = 0)

    CLOSE RESERVAR;

  END;

Answer 1

Franky speaking too many errors in the code. Cant Write them all. Few mistakes:

1. Declare on line-4 not needed.
2. Too many Begin statements.
3. While(@@FETCH_STATUS=0) isnt used for loop termination. Use EXIT WHEN.

4. Missed the Loop beginning & End Loop[Assuming that You are using Loop as you are Cursor in stead of Select Into]

   CREATE OR REPLACE PROCEDURE "USP_MSC_MODIFICA_ESTADO"
   AS
   CURSOR reservar
   IS
   SELECT id_reserva, fch_grabacion
   FROM tb_msc_reserva
   WHERE TO_DATE (TO_CHAR (fch_grabacion, 'dd/mm/yyyy')) =
   TO_DATE (TO_CHAR (SYSDATE, 'dd/mm/yyyy'))
   - 1;
   
   id_reserva      VARCHAR2 (50);
   fch_grabacion   DATE;
   BEGIN
   OPEN reservar;
   
   FETCH reservar
   INTO id_reserva, fch_grabacion;
   
   LOOP
   IF (SELECT TRUNC (  (SYSDATE) - TO_DATE (@fch_grabacion, 'DD/MM/YYYY HH24:MI:SS'))
   FROM DUAL) = 1
   THEN
   UPDATE inv.tb_msc_reserva t
   SET t.flg_estado = 'C'
   WHERE id_reserva = @id_reserva;
   
   COMMIT;
   END IF;
   
   EXIT WHEN (@@fetch_status = 0);
   END LOOP;
   
   CLOSE reservar;
   END;