a better way than casting from a base class to derived class

Base * bases[NUM_ITEMS];
for(int i=0; i<NUM_ITEMS; i++) {
    int r = get_random_integer();
    if(r == 0)
        bases[i] = new Derived1;
    else if(r == 1)
        bases[i] = new Derived2;
    // ...
}

shared_ptr<Base> bases[NUM_ITEMS];
for(int i=0; i<NUM_ITEMS; i++) {
    int r = get_random_integer();
    if(r == 0)
        bases[i].reset(new Derived1);
    else if(r == 1)
        bases[i].reset(new Derived2);
    // ...
}

std::vector< shared_ptr<Base> > bases;
for(int i=0; i<NUM_ITEMS; i++) {
    int r = get_random_integer();
    if(r == 0)
        bases.push_back(shared_ptr<Base>(new Derived1));
    else if(r == 1)
        bases.push_back(shared_ptr<Base>(new Derived2));
    // ...
}

Derived1 * d = &dynamic_cast<Derived1&>(*bases[x]);

shared_ptr<Derived1> d = dynamic_pointer_cast<Derived1>(bases[x]);
if(d) {
    // conversion successful, it pointed to a derived. d and bases[x] point still
    // to the same object, thus share it.
}

interface IShape
    {
       double GetArea();
    }

    class Square : IShape
    {
       double GetArea()
       {
          return sideLengh*sideLength;
       }
       ...
    }

    class FunnyShape : IShape
    {
       //do funny stuff
       ...
    }

    ...

void calcTotalArea(List<IShape> shapes)
{
   double total = 0.0;
   foreach (IShape s in shapes)
   {
      total += s.GetArea();
   }
   return total;
}

class bankAccount
{
   int money;
   bankAccount() {};

   int MoneyInAccount() {return money;};
}

class savingsAccount : public bankAccount
{
   int SavingsInterest();
}

class MoneyMarket : public bankAccount
{
    int CalculateAllPastReturns();
}