google c++ tutorial chapter2 ex1, multithreaded

#include <cstdint>
#include <chrono>
#include <iostream>
#include <atomic>
#include <thread>
#include <vector>

using namespace std;
using namespace std::chrono;
typedef duration<float> fsec;

auto started = steady_clock::now();
atomic<int> counter = 0;

inline int GetNumber()
{
    return ++counter;
}

inline int64_t SigmaN(int64_t n) // to avoid overflow
{
    return n * (n + 1) >> 1;
}

int SerialN(int n)
{
    for (int i = 0; i < n ; ++i)
    {
        if (SigmaN(i) == n)
            return i;
    }

    return 0;
}

int IsPerfectSquare(int n)
{
    if (n < 0)
        return 0;

    int root = (int)(sqrt(n));

    return n == root * root ?
                    root : 0;
}

void Work()
{
    while (true)
    {
        int number = GetNumber();

        if (0 > number)
            break; // until overflow

        int root = IsPerfectSquare(number);

        if (0 < root)
        {
            auto last_of_serial = SerialN(number);

            if (0 < last_of_serial)
            {
                //print elapsed time
                printf("%d = %d^2 = sum(1..%d)\n %0.2f sec\n",
                    number, root, last_of_serial,
                    duration_cast<fsec>(steady_clock::now() - started).count()
                    );
            }
        }
    }//while
}



int main (void)
{
    const size_t sizeofThread = 9;

    vector<thread> workers;

    for (int i = 0; i < sizeofThread; ++i)
    {
        workers.push_back(thread(Work));
    }

    for (auto& t : workers)
        t.join();
}