ORA-06550 error when trying to create PL/SQL procedure - oracle

Question

Something is off but can't figure out what I am missing?
select
grade.sectionid,
grade.studentid,
course.courseid
FROM section
INNER JOIN grade
ON grade.sectionid = section.sectionid
INNER JOIN course
ON course.courseid = section.courseid;
DECLARE
CURSOR mycursor is
select
sectionid, studentid, courseid, coursename
FROM grade, course, section;
var_secID NUMBER(10);
var_studentID NUMBER (10);
var_gradeLetter CHAR(1);
var_coursetitle VARCHAR2(25);
BEGIN
OPEN mycursor;
LOOP
FETCH mycursor
INTO var_secID, var_studentID, var_gradeLetter, var_coursetitle;
EXIT WHEN mycursor%NOTFOUND;
If var_coursetitle(coursename,1) BETWEEN A AND F then
UPDATE grade
SET grade = 'A'
WHERE sectionid;
END IF;
END LOOP;
CLOSE mycursor;
END;
/
Keep getting this error:
ERROR at line 21:
ORA-06550: line 21, column 18:
PL/SQL: ORA-00920: invalid relational operator
ORA-06550: line 19, column 4:
PL/SQL: SQL Statement ignored

Answer 1

BETWEEN A AND F then
should perhaps be:
BETWEEN 'A' and 'F' then

Answer 2

You could do it without any PL/SQL, as:
update grade g set grade = 'A'
where g.sectionid in
( select s.sectionid from section s
join course c on c.courseid = s.courseid
where substr(c.coursename,-1, 1) between 'A' and 'F' );
However as a PL/SQL learning exercise, you could do it without any of the variable or cursor management:
begin
for r in (
select g.sectionid, g.studentid, c.courseid, c.coursename
, substr(c.coursename,-1, 1) as course_lastchar
from grade g
join section s on s.sectionid = g.sectionid
join course c on c.courseid = s.courseid
for update of grade
)
loop
if r.course_lastchar between 'A' and 'F' then
update grade set grade = 'A' where sectionid = r.sectionid;
end if;
end loop;
end;
(btw it's worth getting into the habit of laying code out neatly with a consistent indent size.)