Data Structures, Algorithms, & Applications in C++
Chapter 5, Exercise 11

The code is given below and in the file arrayListWithPush.h. Test code is included in arrayListWithPush.cpp. 
template<class T>
class arrayListWithPush : public arrayList<T> 
{
   public:
      // constructor and destructor
      arrayListWithPush(int initialCapacity = 10)
           : arrayList<T> (initialCapacity) {}

      void push_back(const T& theElement);
};

template<class T>
void arrayListWithPush<T>::push_back(const T& theElement)
{// Insert theElement at right end of list.

   // make sure we have space
   if (listSize == arrayLength)
      {// no space, double capacity
         changeLength1D(element, arrayLength, 2 * arrayLength);
         arrayLength *= 2;
      }


   element[listSize] = theElement;

   listSize++;
}
The complexity of the function is O(1) when the array element doesn't need to be resized; otherwise, the complexity is O(listSize).