#include <atomic>
#include <future>
#include <iostream>
#include <mutex>
#include <thread>

using namespace std;

atomic<int> a(0), b(0);
mutex m;

void  suma()
{
	while (true)
	{
		m.lock();
		++a;
		++b;
		m.unlock();
	}
}

void resta()
{
	while (true)
	{
		m.lock();
		--a;
		--b;
		m.unlock();
	}
}

void muestra()
{
	while (true)
	{
		m.lock();
		cout << "a = " << a << "\t b = " << b << endl;
		m.unlock();
		this_thread::sleep_for(250ms);
	}
}

int main()
{
	thread t[3] = {thread(suma), thread(resta), thread(muestra)};
	for (auto &i: t) i.join();
}