Произведение цифр целого числа

#include <iostream>
#include <numeric>
 
using namespace std;
 
struct number {
public:
    unsigned int value;
    number() : value(0) {}
    number(unsigned int src) : value(src) {}
    unsigned int operator++() { return value /= 10; }
    unsigned int operator*() { return value % 10; }
    bool operator != (const number &other) { return value != other.value; }
};
 
istream & operator>>(istream &is, number &n) {
    return is >> n.value;
}
 
int main() {
    number n;
    cout << "Введите число: ";
    cin >> n;
    cout << accumulate<number, int>(n, 0, 1, multiplies<int>());
}

#include <iostream>
#include <numeric>
#include <string>
 
int main()
{
    const int N = 1234;
    std::string s = std::to_string(N);
    const int M = std::accumulate(s.cbegin(), s.cend(), 1, [](const int x, const char y) { return x * (y - '0'); });
    std::cout << M << std::endl;
}