SQL & PL/SQL

hi guys ...
I'm having a problem creating this procedure and I can't solve this problem
Do you have a solution or any tips?
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Goal from procedure:
to print employee name and grades based on salary.
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Problem/Error:
Compilation failed,line 13 (13:52:34)
PLS-00201: identifier 'CURSOR' must be declaredCompilation failed,line 13 (13:52:34)
PL/SQL: SQL Statement ignoredCompilation failed,line 41 (13:52:34)
PLS-00201: identifier 'CURSOR' must be declaredCompilation failed,line 41 (13:52:34)
PL/SQL: SQL Statement ignored
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Code/sql pl:
create or replace PROCEDURE printgrades is
CURSOR nasa IS SELECT ename, sal FROM emp;
r_nasa nasa%ROWTYPE;
BEGIN
--open cursor to allocate memory for cursor
IF NOT nasa%ISOPEN THEN
OPEN CURSOR;
END IF;
--start point of looping on the cursor
LOOP
--fetching data from cursor
FETCH nasa INTO r_nasa;
DBMS_OUTPUT.PUT(r_nasa.ename || ', ');
--classification of employees according to salary
CASE
WHEN r_nasa.sal>1 AND r_nasa.sal<=1000 THEN
DBMS_OUTPUT.PUT('LESS THAN 1000');
WHEN r_nasa.sal>1000 AND r_nasa.sal<=2000 THEN
DBMS_OUTPUT.PUT('BETWEEN 1000 & 2000');
WHEN r_nasa.sal>2000 AND r_nasa.sal<=3000 THEN
DBMS_OUTPUT.PUT('BETWEEN 2000 & 3000');
WHEN r_nasa.sal>3000 THEN
DBMS_OUTPUT.PUT('GREATER THAN 3000');
ELSE
DBMS_OUTPUT.PUT('Invailed salary value!');
END CASE;
--condition to prevent infinite looping
EXIT WHEN nasa%NOTFOUND;
--end point of looping on the cursor
END LOOP;
--close cursor to release the allocated memory
IF nasa%ISOPEN THEN
CLOSE CURSOR;
END IF;
END printgrades;​
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