Arithmetic progression

#include <iostream>
#include <cstdlib>
#include <vector>

using namespace std;

int main()
{
    // d, n, a1,an
    // an - posledniq chlen ; sn - sumata na chlenovete; an1 - temp chlen
    double a1, n, d, an;
    double sn;
    cout << "Purvit chlen e: ";cin >> a1; cout << "Razlikata e: "; cin >> d; cout << "Broq e "; cin >> n; cout << endl;
    int d1 = d;

    vector <double> prog = { };

    an = a1 + (n - 1) / d;
    sn = (a1 + an) / 2 * n;

    for (int i = a1; i <= sn; i++)
    {
        if (i % d1 == 0)
        {
            prog.push_back(i);
        }
    }

    for (int i = 0; i <n; i++)
    {
        cout << prog[i] << " ";
    }

    //cout << "an: " << an << endl;
    //cout << "sn: " << sn << endl;
}