[oracle] How to use a variable from a cursor in the select statement of another cursor in pl/sql

You can certainly do something like

SQL> ed
Wrote file afiedt.buf

  1  begin
  2    for d in (select * from dept)
  3    loop
  4      for e in (select * from emp where deptno=d.deptno)
  5      loop
  6        dbms_output.put_line( 'Employee ' || e.ename ||
  7                              ' in department ' || d.dname );
  8      end loop;
  9    end loop;
 10* end;
SQL> /
Employee CLARK in department ACCOUNTING
Employee KING in department ACCOUNTING
Employee MILLER in department ACCOUNTING
Employee smith in department RESEARCH
Employee JONES in department RESEARCH
Employee SCOTT in department RESEARCH
Employee ADAMS in department RESEARCH
Employee FORD in department RESEARCH
Employee ALLEN in department SALES
Employee WARD in department SALES
Employee MARTIN in department SALES
Employee BLAKE in department SALES
Employee TURNER in department SALES
Employee JAMES in department SALES

PL/SQL procedure successfully completed.

Or something equivalent using explicit cursors.

SQL> ed
Wrote file afiedt.buf

  1  declare
  2    cursor dept_cur
  3        is select *
  4             from dept;
  5    d dept_cur%rowtype;
  6    cursor emp_cur( p_deptno IN dept.deptno%type )
  7        is select *
  8             from emp
  9            where deptno = p_deptno;
 10    e emp_cur%rowtype;
 11  begin
 12    open dept_cur;
 13    loop
 14      fetch dept_cur into d;
 15      exit when dept_cur%notfound;
 16      open emp_cur( d.deptno );
 17      loop
 18        fetch emp_cur into e;
 19        exit when emp_cur%notfound;
 20        dbms_output.put_line( 'Employee ' || e.ename ||
 21                              ' in department ' || d.dname );
 22      end loop;
 23      close emp_cur;
 24    end loop;
 25    close dept_cur;
 26* end;
 27  /
Employee CLARK in department ACCOUNTING
Employee KING in department ACCOUNTING
Employee MILLER in department ACCOUNTING
Employee smith in department RESEARCH
Employee JONES in department RESEARCH
Employee SCOTT in department RESEARCH
Employee ADAMS in department RESEARCH
Employee FORD in department RESEARCH
Employee ALLEN in department SALES
Employee WARD in department SALES
Employee MARTIN in department SALES
Employee BLAKE in department SALES
Employee TURNER in department SALES
Employee JAMES in department SALES

PL/SQL procedure successfully completed.

However, if you find yourself using nested cursor FOR loops, it is almost always more efficient to let the database join the two results for you. After all, relational databases are really, really good at joining. I'm guessing here at what your tables look like and how they relate based on the code you posted but something along the lines of

FOR x IN (SELECT *
            FROM all_users,
                 org
           WHERE length(all_users.username) = 3
             AND all_users.username = org.username )
LOOP
  <<do something>>
END LOOP;