DECLARE
    p NUMBER := 0;
    q NUMBER := 1;
    r NUMBER;
BEGIN
    DBMS_OUTPUT.PUT_LINE(LPAD('0: ', 4) || LPAD(p, 10));
    DBMS_OUTPUT.PUT_LINE(LPAD('1: ', 4) || LPAD(q, 10));
    FOR k IN 2..20 LOOP
        r := p + q;
            DBMS_OUTPUT.PUT_LINE(LPAD(k, 2) || ': ' || LPAD(r, 10));
            p := q;
            q := r;
    END LOOP;
END;

We went over this in one of my classes but I didnt really get a good understanding to how this for loop works. I know the output prints numbers 0-20 on the left and I am confused at how the numbers on the right increase as they do.

the sequence printed are the fibonacci numbers. their recursive definition reads: a_n = a_(n-1) + a_(n-2). in the code snippet, p takes the role of a_(n-2), q that of a_(n-1). imagine the sequence printed out from the right to the left with a sliding window (r, q, p) superimposed. in each iteration, the window moves one step to the left. the lpad function pads a string to the given length. you may optionally add a 3rd argument, the padding character (defaults to ). notet that there is a sibling function rpad. but you probably know this if the code has been discussed in class.