How to work with CURSOR in PL/SQL?

Question

I have table RADNIK filled with some test data and containing 21 rows. When I execute simple SELECT command like: SELECT ime, prz, plt FROM RADNIK; it gives me expected result.

I decided to learn PL/SQL and I wrote this code:

DECLARE
    CURSOR c_radnik IS 
        SELECT ime, prz, plt FROM RADNIK;
    rec_radnik c_radnik%ROWTYPE;
BEGIN
    OPEN c_radnik;
    LOOP
        FETCH c_radnik INTO rec_radnik;
        EXIT WHEN c_radnik%NOTFOUND;
        DBMS_OUTPUT.PUT_LINE(rec_radnik.ime || ' ' 
            || rec_radnik.prz || ' ' 
            || rec_radnik.plt);
    END LOOP;
    CLOSE c_radnik;
END;

After executing this code, I got only message: PL/SQL procedure successfully completed.

I don't know what is wrong.