CounterGenerator.cpp

#include <iostream>
using namespace std;

// Counts numbers from 0 to n-1.
struct Counter {
    int i = 0;
    int n;
    bool first = true; // Tracks if this is the first invocation of the next() function
    Counter(int _n): n(_n) {}
    int* next() {
        if (i == n) return nullptr;
        if (!first) goto cx;
        first = false;
        while (i < n) {
            return &i; // yield the next value in the sequence
            cx: // We continue from here on the next invocation of this function
            ++i;
        }
        return nullptr;
    }
};

int main() {
    Counter c(10);
    int *n = c.next();
    while (n) {
        cout << *n << ", ";
        n = c.next();
    }
    cout << endl;
}