optional and timer in boost and sprout

// sudo apt-get install libboost-all-dev
// g++ prog.cc -Wall -Wextra -I/opt/wandbox/boost-1.73.0/gcc-head/include -std=c++2b
// clang++ prog.cc -Wall -Wextra -I/opt/wandbox/boost-1.69.0/clang-7.0.0/include -std=c++11
//
#include <iostream>
#include <string>

#define BOOST  // #define SPROUT

#if defined(BOOST)
#include <boost/optional.hpp> // boost 1.63.0
#include <cstdlib>
#include <boost/timer/timer.hpp>
#elif defined(SPROUT)
#include <sprout/optional.hpp> // sprout not boost
#endif

#if defined(BOOST)
boost::optional<int> f(int n)
{
    return { n };
}
#elif defined(SPROUT)
sprout::optional<int> f(int n)
{
    return { n };
}
#endif

int main()
{
#if defined(BOOST)
    const auto n1 = f(23);

    if (n1) std::cout << "note its a pointer " << *n1 << std::endl;

    const long n=10000000;
    {
        boost::timer::cpu_timer timer;

        for (long i = 0; i < n; ++i) {
        // DO 1
        }

        std::string result = timer.format();
        std::cout << result << std::endl;
    }
    {
        boost::timer::cpu_timer timer;

        for (long i = 0; i < n; ++i) {
        // DO 2
        }

        std::string result = timer.format();
        std::cout << result << std::endl;
    }

#elif defined(SPROUT)
    const auto n = f(23);
    for (int i : n) std::cout << "the value using sprout " << i << std::endl;
#endif

}