{

factorial(int x, int& res) : x(x), res(res) { }

void operator()() { res = calculate(x); }

int result() const { return res; }

int calculate(int x) { return x <= 1 ? 1 : x * calculate(x-1); }

int x;

int& res;

{

int results[NUM_CALCS];

boost::thread_group thrds;

for (int i=0; i < NUM_CALCS; ++i)

thrds.create_thread(factorial(i*10, results[i]));

thrds.join_all();

for (int j=0; j < NUM_CALCS; ++j)

std::cout << j*10 << "! = " << results[j] << std::endl;