Bottom to top traverse of an associative array using Oracle PL/SQL - Oracle

In the last sections, we have already seen several pre-defined members associated with associative arrays.  Now, let us look into the same scenario with a small difference in traversing.

The last two sections concentrated on a top-down approach to traversing an associative array.  Now, we shall focus on a bottom-top approach to traversing the same.  Let us first go through the code:

declare
      type year_type is table of number index by binary_integer;
      year_sales year_type;
      tot_sales   number := 0;
      i           number;
begin
      year_sales(1990) := 34000;
      year_sales(1991) := 45000;
      year_sales(1992) := 43000;
      year_sales(1996) := 13000;
      year_sales(1998) := 53000;

      i := year_sales.last;
      while i >= year_sales.first
      loop
            tot_sales := tot_sales + year_sales(i);
            dbms_output.put_line('Sales of ' || i || ': ' ||
year_sales(i));
            i := year_sales.prior(i);
      end loop;
      dbms_output.put_line('Total sales: ' || tot_sales);
      dbms_output.put_line('Avg sales: ' ||
(tot_sales/year_sales.count) );

end;

Shown below are the only modifications I made to the above code.  I replaced the following:

i := year_sales.first;
      while i <= year_sales.last
      loop
            tot_sales := tot_sales + year_sales(i);
            dbms_output.put_line('Sales of ' || i || ': ' ||
year_sales(i));
            i := year_sales.next(i);
      end loop;

with this:

      i := year_sales.last;
      while i >= year_sales.first
      loop
            tot_sales := tot_sales + year_sales(i);
            dbms_output.put_line('Sales of ' || i || ': ' ||
year_sales(i));
            i := year_sales.prior(i);
      end loop;

Please observe the color highlighting in the code fragments above.  The rest is the same, and I leave it for you to understand.