std::thread

thread std lib allows us to spawn threads in cpp on demand, join() them or detach() them as per the requirement.

Thread execution is started as soon as it is created with as task.

#include <iostream>
#include <thread>
#include <chrono>
#include <algorithm>
using namespace std;
using namespace std::chrono;
typedef long long int ull;

void findEven(ull start, ull end, ull *EvenSum)
{
    for (ull i = start; i <= end; ++i)
    {
        if (!(i & 1))
        {
            *(EvenSum) += i;
        }
    }
}

void findOdd(ull start, ull end, ull *OddSum)
{
    for (ull i = start; i <= end; ++i)
    {
        if (i & 1)
        {
            (*OddSum) += i;
        }
    }
}

int main()
{
    ull start = 0, end = 1900000000;

    ull OddSum = 0;
    ull EvenSum = 0;

    auto startTime = high_resolution_clock::now();

    // // WITH THREAD
    std::thread t1(findEven, start, end, &(EvenSum));
    std::thread t2(findOdd, start, end, &(OddSum));

    t1.join();
    t2.join();

    // // WITHOUT THREAD
    // findEven(start,end, &EvenSum);
    // findOdd(start, end, &OddSum);
    auto stopTime = high_resolution_clock::now();
    auto duration = duration_cast<microseconds>(stopTime - startTime);

    cout << "OddSum : " << OddSum << endl;
    cout << "EvenSum : " << EvenSum << endl;

    cout << "Sec: " << duration.count() / 1000000 << endl;

    return 0;
}

Try this here.