"Improved" seven boom by `hasSeven()` being a one op and only the first digit tracking divisibility

sevenboom2.cpp

#include <memory>
#include <ranges>
#include <iostream>

class Digit {
	unsigned char val;
	std::unique_ptr<Digit> moreSignificant;
	static unsigned int sevens;
public:
	Digit(unsigned char startVal) : val(startVal) {}
	virtual void inc() {
		if (val == 7)
			sevens--;
		if (++val > 9) {
			val = 0;
			if (moreSignificant)
				moreSignificant->inc();
			else
				moreSignificant = std::make_unique<Digit>(1);
		}
		if (val == 7)
			sevens++;
	}
	virtual bool hasSeven() {
		return sevens > 0;
	}
};

unsigned int Digit::sevens = 0;

class FirstDigit : public Digit {
	unsigned char sevenCount;
public:
	FirstDigit(unsigned char startVal) : Digit(startVal), sevenCount(startVal % 7) { }
	virtual void inc() {
		Digit::inc();
		if (++sevenCount >= 7)
			sevenCount = 0;
	}
	virtual bool isDivisibleBySeven() {
		return sevenCount == 0;
	}
};

int main() {
	FirstDigit num(0);
	for (unsigned long long i : std::ranges::views::iota(1ULL, 100000ULL)) { // while (true)
		num.inc();
		if (num.hasSeven() || num.isDivisibleBySeven())
			std::cout << "BOOM" << std::endl;
		else
			std::cout << i << std::endl;
	}
}