Thread: Sieve of Eratosthenes

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 ;
}

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.

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