Multi-field dynamic array

I'm sure this has been asked before but I can't seem to find what I'm
looking for in the archives

I'll post the code that I have to help paint the picture
D AddItmIdx       S              5S 0 Inz(0) 
D BuyItmIdx       S              5S 0 Inz(0)
D                 DS
D BuyerInfo                     56A   DIM(1)
D   Buyer                        3A   Overlay(BuyerInfo:1)
D   Item                        27A   Overlay(BuyerInfo:4)
D   Quantity                    11S 2 Overlay(BuyerInfo:31)
D   LastPurch                    8S 0 Overlay(BuyerInfo:43)
D   Vendor                       6A   Overlay(BuyerInfo:51)

/Free

 BuyItmIdx = %LookUp(PBITNO:Item);
 IF BuyItmIdx > 0;
    Quantity(BuyItmIdx) = PBORQT;

    If WrkDate > LastPurch(BuyItmIdx);
       LastPurch(BuyItmIdx) = WrkDate;
    EndIF;

Else;
    AddItmIdx += 1;
    Buyer(AdditmIdx) = PBVNNO;
    Item(additmidx) = PBITNO;
    Quantity(Additmidx) = PBORQT;
    LastPurch(AddItmIdx) = WrkDate;
    Vendor(AddItmIdx) = PBVNNO;
 EndIF;

/Free
I want to be able to increase the size of the array on an as needed
basis. I'm pretty sure this can be done with pointers, but I can't
figure out how. Can anyone offer some suggestions?