C++ Square Calculator

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

using namespace std;
using namespace std::chrono;

class SquareCalculator
{
private:
    int start;
    int end;
    long long executionTime;
    vector<int> results;

public:
    SquareCalculator(int start, int end) : start(start), end(end), executionTime(0) {}

    vector<int> getResults() const
    {
        return results;
    }

    long long getExecutionTime() const
    {
        return executionTime;
    }

    void operator()()
    {
        auto startTime = high_resolution_clock::now();
        for (int i = start; i <= end; i++)
        {
            int square = i * i;
            results.push_back(square);
        }
        auto endTime = high_resolution_clock::now();
        executionTime = duration_cast<milliseconds>(endTime - startTime).count();
    }
};

int main()
{
    const int numbers = 100'000'000;
    const int numThreads = 1;
    const int numbersPerThread = numbers / numThreads;

    vector<SquareCalculator> calculators;
    for (int i = 0; i < numThreads; i++)
    {
        int start = i * numbersPerThread + 1;
        int end = (i + 1) * numbersPerThread;
        calculators.emplace_back(start, end);
    }

    auto startTime = high_resolution_clock::now();
    vector<thread> threads;
    for (auto &calculator : calculators)
    {
        threads.emplace_back(ref(calculator));
    }

    for (auto &thread : threads)
    {
        thread.join();
    }
    auto endTime = high_resolution_clock::now();

    for (size_t i = 0; i < calculators.size(); i++)
    {
        cout << "Thread " << i << " took " << calculators[i].getExecutionTime() << "ms" << endl;
    }

    cout << "Time taken: " << duration_cast<milliseconds>(endTime - startTime).count() << "ms" << endl;

    return 0;
}