Prime numbers integral by Eratosthenes

gistfile1.cpp

int64_t nn = 100000000;
vector<int> ip(nn,1);
size_t pos = 2;
ip[0] = 0;
ip[1] = 0;
while ((pos = find(ip.begin()+pos, ip.end(), 1) - ip.begin()) < nn) {
    for (size_t j = pos*pos; j < ip.size(); j+=pos)
        ip[j] = 0;
    pos += 1 + (pos>2);
}
for (int i = 1; i < nn; i++)
    ip[i] += ip[i-1];