Task: Intersecting number wheels
C#: using System;
using System.Collections.Generic;
using System.Linq;

public static class IntersectingNumberWheels
{
    public static void Main() {
        TurnWheels(('A', "123")).Take(20).Print();
        TurnWheels(('A', "1B2"), ('B', "34")).Take(20).Print();
        TurnWheels(('A', "1DD"), ('D', "678")).Take(20).Print();
        TurnWheels(('A', "1BC"), ('B', "34"), ('C', "5B")).Take(20).Print();
    }

    static IEnumerable<char> TurnWheels(params (char name, string values)[] wheels) {
        var data = wheels.ToDictionary(wheel => wheel.name, wheel => wheel.values.Loop().GetEnumerator());
        var primary = data[wheels[0].name];
        while (true) {
            yield return Turn(primary);
        }

        char Turn(IEnumerator<char> sequence) {
            sequence.MoveNext();
            char c = sequence.Current;
            return char.IsDigit(c) ? c : Turn(data[c]);
        }
    }

    static IEnumerable<T> Loop<T>(this IEnumerable<T> seq) {
        while (true) {
            foreach (T element in seq) yield return element;
        }
    }

    static void Print(this IEnumerable<char> sequence) => Console.WriteLine(string.Join(" ", sequence));
}

C++: #include <initializer_list>
#include <iostream>
#include <map>
#include <vector>

struct Wheel {
private:
    std::vector<char> values;
    size_t index;

public:
    Wheel() : index(0) {
        
    }

    Wheel(std::initializer_list<char> data) : values(data), index(0) {
        
        if (values.size() < 1) {
            throw new std::runtime_error("Not enough elements");
        }
    }

    char front() {
        return values[index];
    }

    void popFront() {
        index = (index + 1) % values.size();
    }
};

struct NamedWheel {
private:
    std::map<char, Wheel> wheels;

public:
    void put(char c, Wheel w) {
        wheels[c] = w;
    }

    char front(char c) {
        char v = wheels[c].front();
        while ('A' <= v && v <= 'Z') {
            v = wheels[v].front();
        }
        return v;
    }

    void popFront(char c) {
        auto v = wheels[c].front();
        wheels[c].popFront();

        while ('A' <= v && v <= 'Z') {
            auto d = wheels[v].front();
            wheels[v].popFront();
            v = d;
        }
    }
};

void group1() {
    Wheel w({ '1', '2', '3' });
    for (size_t i = 0; i < 20; i++) {
        std::cout << ' ' << w.front();
        w.popFront();
    }
    std::cout << '\n';
}

void group2() {
    Wheel a({ '1', 'B', '2' });
    Wheel b({ '3', '4' });

    NamedWheel n;
    n.put('A', a);
    n.put('B', b);

    for (size_t i = 0; i < 20; i++) {
        std::cout << ' ' << n.front('A');
        n.popFront('A');
    }
    std::cout << '\n';
}

void group3() {
    Wheel a({ '1', 'D', 'D' });
    Wheel d({ '6', '7', '8' });

    NamedWheel n;
    n.put('A', a);
    n.put('D', d);

    for (size_t i = 0; i < 20; i++) {
        std::cout << ' ' << n.front('A');
        n.popFront('A');
    }
    std::cout << '\n';
}

void group4() {
    Wheel a({ '1', 'B', 'C' });
    Wheel b({ '3', '4' });
    Wheel c({ '5', 'B' });

    NamedWheel n;
    n.put('A', a);
    n.put('B', b);
    n.put('C', c);

    for (size_t i = 0; i < 20; i++) {
        std::cout << ' ' << n.front('A');
        n.popFront('A');
    }
    std::cout << '\n';
}

int main() {
    group1();
    group2();
    group3();
    group4();

    return 0;
}