You declared binarylist as a function above (in bold).
class BigInt : public DList
//BigInt toBigInt(DList list);
void toBinary(DList list);
But you use it as an object here. I assume those are supposed to be member variables, not functions.
void BigInt::toBinary(DList list)
int size = list.size();
for(int i=0, compare;i<size;i++)
compare = 8;
temp = list.at(i);
if(temp >= compare)
temp -= compare;
compare /= 2;
PS. If they are member variables then that also makes me wonder why BigInt derives from DList and also contains two DLists.