Adding iterators to a class for use in ranged-for loops. See https://godbolt.org/z/4FLhuY

iterators.cpp

#include <iostream>
#include <string>

using namespace std;

template <typename T>
class Ring
{
    private:
        int m_size;
        T* m_data;
        int m_pos;
    
    public:
        Ring(int const t_size) : m_size{t_size}, m_data{ new T[m_size]}, m_pos{0} {}

        ~Ring() {
            delete [] m_data;
            cout << "Destructed." << endl;
        }

        void add(T const t_arg) {
            m_data[m_pos++] = t_arg;
            if (m_pos == m_size) m_pos = 0;
        }

        int size() const { return m_size; }

        T& get(int const t_index) const { return m_data[t_index]; }

        class iterator;

        iterator begin() {
            return iterator(0, *this);
        }

        iterator end() {
            return iterator(m_size, *this);
        }

};

template <typename T>
class Ring<T>::iterator
{
    private:
        int m_pos;
        Ring& m_ring;
    
    public:
        iterator(int t_pos, Ring& t_ring) : m_pos{t_pos}, m_ring{t_ring} {}

        bool operator!=(iterator const& t_other) const { return m_pos != t_other.m_pos; }

        // Postfix ++
        iterator& operator++(int) {
            m_pos++;
            return *this;
        }

        // Prefix ++, required for C++ 11 style ranged-for
        iterator& operator++() {
            m_pos++;
            return *this;
        }

        // Postfix --
        iterator& operator--(int) {
            m_pos--;
            return *this;
        }

        T& operator*() { return m_ring.get(m_pos); }

};


int main() {

    Ring<string> textring(3);
    textring.add("one");
    textring.add("two");
    textring.add("three");
   
    // Output one, two, three
    for(int i = 0; i < textring.size(); i++) {
       cout << textring.get(i) << endl;
    }

    cout << endl;

    textring.add("four");
    textring.add("five");

    // Output four, five, three
    // C++ 98 style
    for(Ring<string>::iterator it = textring.begin(); it != textring.end(); it++) {
        cout << *it << endl;
    }

    cout << endl;

    auto end = textring.end();
    *end-- = "six";

    // Output four, five, six
    // C++ 11 style
    for (auto value: textring) {
        cout << value << endl;
    }

    return 0;
}