754: Practice

A popular alternative to storing railroad_car objects in either ordinary arrays or lists is to store them in self-expanding arrays. A self-expanding array is an array that gets larger as more and more elements are added to it.

You can implement a self-expanding array as follows:

• Define a self_expanding_array class that contains a member variable assigned to an internal array of objects.
• Define class reader and writer member functions that read from and write into the internal array.
• Modify the writer such that, if a program attempts to write into a location that does not exist, a new, larger array is created, the old array is copied into the new array, and the old array is destroyed.
• Modify the reader such that, if a program attempts to read from a location that does not exist, an error message is displayed.

The following definition of the Integer_array class embodies the first two steps toward the creation of a self-expanding array of integers:

#include   
// Define global integer array: 
class Integer_array { 
  public: // Constructor: 
          Integer_array ( ) { 
            hidden_array = new int[100]; 
          } 
          // Reader: 
          int read_element (int n) { 
            return hidden_array[n]; 
          } 
          // Writer: 
          void write_element (int n, int i) { 
            hidden_array[n] = i; 
          } 
  private: int* hidden_array; 
}; 

Modify the definition so as to complete the development.