C++ Random Integer 0-99 Array optimization

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

class RandomCounterArray
{
private:
    int start;
    int end;
    std::vector<int> results;

public:
    RandomCounterArray(int start, int end) : start(start), end(end), results(100, 0) {}

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

    int getLength() const
    {
        int length = 0;
        for (int value : results)
        {
            length += value;
        }
        return length;
    }

    void operator()()
    {
        auto startTime = std::chrono::steady_clock::now();
        for (int i = start; i <= end; i++)
        {
            int result = randomInt();
            results[result]++;
        }
        auto endTime = std::chrono::steady_clock::now();
        std::chrono::duration<double, std::milli> duration = endTime - startTime;
        std::cout << "Thread took " << duration.count() << "ms" << std::endl;
    }

private:
    int randomInt()
    {
        return rand() % 100;
    }
};

int main()
{
    srand(time(nullptr));

    int numbers = 10000000;
    int numThreads = 1;
    int numbersPerThread = numbers / numThreads;
    std::vector<std::thread> threads;

    for (int i = 0; i < numThreads; i++)
    {
        int start = i * numbersPerThread + 1;
        int end = (i + 1) * numbersPerThread;
        threads.emplace_back(RandomCounterArray(start, end));
    }

    auto startTime = std::chrono::steady_clock::now();

    for (auto &thread : threads)
    {
        thread.join();
    }

    auto endTime = std::chrono::steady_clock::now();
    std::chrono::duration<double, std::milli> duration = endTime - startTime;

    std::cout << "Time taken: " << duration.count() << "ms" << std::endl;

    return 0;
}