struct particle
{
    int index;
    double x;
    double y;
    vector<int> nn;
};

vector<particle> cluster;
//initiate the "x" and "y" values of the particles
particle tmp;
for (int i = 0; i < 10; i++)
{
        tmp.index = i;
        tmp.x = 1.1*i;
        tmp.y = 2.2*i;
        cluster.push_back(tmp);
}

vector<int> nnn;
for (int i = 0; i < 5; i++)
{
    bla.push_back(i);
}
cluster[0].nn.push_back(bla);

for (int i = 0; i < 5; i++)
{
        cluster[0].nn.push_back(j);
}