#include <iostream>
#include <chrono>

int main() {

    using namespace std::chrono;

    seconds sec(5);

    milliseconds ms = duration_cast<milliseconds>(sec);

    std::cout << "5 seconds is " << ms.count() << " milliseconds.\n";

    return 0;
}

When converting between different time units using std::chrono in C++, the typical approach is to use the duration_cast function. This ensures that conversions are precise and explicit.