Dynamic variable in PL/SQL

I have done the following code for an assignment:

DECLARE
   Ledger_rec   DDI.LEDGER_VIEW%ROWTYPE;

   PROCEDURE Var2Count(v_col IN NUMBER)
      IS
      BEGIN
         DBMS_OUTPUT.PUT(TO_CHAR(NVL(v_col,0), '999,999'));
      END;
BEGIN
   DBMS_OUTPUT.PUT_LINE('                  Total Head Count by Registration Date');
   DBMS_OUTPUT.NEW_LINE;
   DBMS_OUTPUT.PUT_LINE('REGDATE               101     102     103     104     105     106     107     108');
   DBMS_OUTPUT.PUT_LINE('--------             -----   -----   -----   -----   -----   -----   -----   -----');
   FOR Ledger_rec IN
      (
       SELECT * FROM
         (
          SELECT REGDATE, ADULTCNT, CHILDCNT, ROOMNUM
          FROM DDI.LEDGER_VIEW
         )
         PIVOT
         (
          SUM(CHILDCNT + ADULTCNT)
          FOR ROOMNUM IN ('101' AS r101,
                             '102' AS r102,
                             '103' AS r103,
                             '104' AS r104,
                             '105' AS r105,
                             '106' AS r106,
                             '107' AS r107,
                             '108' AS r108)
         )
       ORDER BY REGDATE
       )
    LOOP
       DBMS_OUTPUT.PUT(RPAD(Ledger_rec.REGDATE, 16));
       Var2Count(Ledger_rec.r101);
       Var2Count(Ledger_rec.r102);
       Var2Count(Ledger_rec.r103);
       Var2Count(Ledger_rec.r104);
       Var2Count(Ledger_rec.r105);
       Var2Count(Ledger_rec.r106);
       Var2Count(Ledger_rec.r107);
       Var2Count(Ledger_rec.r108);
       DBMS_OUTPUT.NEW_LINE;
    END LOOP;

EXCEPTION
   WHEN NO_DATA_FOUND THEN
   DBMS_OUTPUT.PUT_LINE('No data found.');
END;

This is working except there is one thing I am missing from the assignment description:

Use the dynamic variable, (CHILDCNT + ADULTCNT) HEADCNT, for the aggregate SUM(HEADCNT)

So, I think my code should read SUM(HEADCNT). How do I assign and use this dynamic variable?