// main.cpp
#include "tools/sieve.h"
#include <iostream>

int main()
{
    std::vector<long> testing{ tools::getSieves(100) };
    for (auto &t : testing)
    {
        std::cout << t << ' ';
    }
    return 0;
}

// tools/sieve.h
#ifndef SIEVE_H
#define SIEVE_H

#include <vector>

namespace tools
{
    std::vector<long> getSieves(int max);
};

#endif // !SIEVE_H

// tools/sieve.cpp
#include <vector>

namespace tools
{

    std::vector<long> getSieves(int max)
    {
        bool table[max+1];
        for (int x = 0; x <= max; x++)
            table[x] = true;
        for (int i = 2; i*i <= max; i++)
            if (table[i] == true)
                for (int j = i*2; j <= max; j += i)
                    table[j] = false;
        std::vector<long> sieves{};
        for (int i = 2; i <= max; i++)
            if (table[i])
                sieves.push_back(i);
        return sieves;
    }

}