this is attempt for sieve of Eras algorithm...but it works freaking slow for numbers above 10000..i was wondering is there a way to make it faster (I am yet to try the Euler sieve algorithm..but I don't see how it is any different)? I don't think it would make any difference if i used vectors..and i don't know how to use vectors anyway.Code:#include <iostream> #include <list> using namespace std ; #define SIZE 10 int main() { list<unsigned long int> sieve ; list<unsigned long int>::iterator it ; long int i =2 ; while(i<SIZE) { sieve.push_back(i) ; i++ ; } it = sieve.begin() ; i=*it; unsigned long int sum =0; while(i*i < SIZE) { i = *it ; sieve.push_back(*it) ; it = sieve.erase(it) ; while(it!=sieve.end()) { if(i!=*it&&(*it)%i==0) { it = sieve.erase(it) ; } else { it++ ; } } it = sieve.begin() ; } it = sieve.begin() ; while(it!=sieve.end()) { sum+=*it ; it++ ; } cout << "Sum of all prime is: " << sum ; cin.get() ; return 0 ; }

One more thing..when I remove the multiples from a list and i increment the iterator, the program crashes i had to use an else for that, to increment the iterator if an element is not erased.

I don't understand why it crashes, i mean

i would safely assume that when I removed from a list and incremented the list thereafter the iterator would point to valid address if there was an element after it. But since I can't be sure, it is better to use the else to increment the iterator if not erased... :S