Reference: Data Structures and Algorithms with Object-Oriented Design Patterns in C++

#include <iostream>
#include <stdexcept> // std::out_of_range
using namespace std;

template <class T>

class Array
{
protected:
    T* data;
    unsigned int base;
    unsigned int length;
public:
    Array();
    Array(unsigned int, unsigned int = 0);
    ~Array();

    Array(Array const&);
    Array& operator = (Array const&);

    T const& operator [] (unsigned int) const;
    T& operator [] (unsigned int);

    T const* Data() const;
    unsigned int Base() const;
    unsigned int Length() const;

    void SetBase(unsigned int);
    void SetLength(unsigned int);
};

template <class T>
Array<T>::Array()
{
    data = new T[0];
    base = 0;
    length = 0;
}

template <class T>
Array<T>::Array(unsigned int n, unsigned int m)
{
    data = new T[n];
    base = m;
    length = n;
}

template <class T>
Array<T>::Array(Array<T> const& array)
{
    data = new T[array.length];
    base = array.base;
    length = array.length;
    for(unsigned int i = 0; i<length; i++)
        data[i] = array.data[i];
}

template <class T>
Array<T>::~Array()
{
    delete [] data;
}

template <class T>
T const* Array<T>::Data() const
{
    return data;
}

template <class T>
unsigned int Array<T>::Base() const
{
    return base;
}

template <class T>
unsigned int Array<T>::Length() const
{
    return length;
}

template <class T>
T const& Array<T>::operator [] (unsigned int position) const
{
    unsigned int const offset = position - base;
    if(offset >= length)
        throw out_of_range("invalid position");
    return data[offset];
}

template <class T>
T& Array<T>::operator [] (unsigned int position)
{
    unsigned int const offset = position - base;
    if(offset >= length)
        throw out_of_range("invalid position");
    return data[offset];
}

template <class T>
void Array<T>::SetBase(unsigned int newBase)
{
    base = newBase;
}

template <class T>
void Array<T>::SetLength(unsigned int newLength)
{
    T* const newData = new T[newLength];
    unsigned int const min = length < newLength ? length : newLength;
    for(unsigned int i = 0; i<min; i++)
        newData[i] = data[i];
    delete [] data;
    data = newData;
    length = newLength;
}

int main()
{
    Array<int> array(5,0);
    array[0] = 10;
    array[1] = 20;
    return 0;
}