#include <stdlib.h>
#include <iostream>
#include <assert.h>

template<int Capcity>
class cbuffer
{
public:
    cbuffer() : sz(0), p(0){}
    void push_back(int n)
    {
        buf[p++] = n;
        if (sz < Capcity)
            sz++;
        if (p >= Capcity)
            p = 0;
    }
    int size() const
    {
        return sz;
    }
    int operator[](int n) const
    {
        assert(n < sz);
        n = p - sz + n;
        if (n < 0)
            n += Capcity;
        return buf[n];
    }
    int buf[Capcity];
    int sz, p;
};

int main()
{
    cbuffer<5> buf;

    // insert random 100 numbers
    for (int i = 0; i < 100; ++i)
        buf.push_back(rand());

    // output to cout contents of the circular buffer
    for (int i = 0; i < buf.size(); ++i)
        std::cout << buf[i] << ' ';
}