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Cannot copy vector

rozick1 (218)
Hi all,

I've created a sieve of eratosthenes. The intial vector contains numbers 1- howmany and then replaced with 0 if not prime.

I want to remove the 0s. Instead of deleting vector elements I created a new vector to copy all non-0 elements but the program keeps crashing (when howmany is more than 100).

Any help would be great.

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#include <iostream>
#include <vector>
#include <fstream>

using namespace std;

int main()
{
    //initialise//
    int howmany=1000;

    vector <int> primes (howmany);

    for (int a=1;a<howmany;a++)
    {
        primes[a] = a;
    }

    //sieve


    for (int b=2;b<howmany;b++)
    {
        if (primes[b] == 0)
        {
            continue;
        }

        bool mult =true;
        int c=2;
            while (mult)
            {

                if ((c*b)>howmany)
                {
                    break;
                }


                primes[c*b]=0;

                c++;
            }

    }

//copy
vector <int> copied;

for ( int p=0;p<howmany;p++)
{
    if (primes[p]!=0)
    copied.push_back(primes[p]);
}



}
Peter87 (11222)
primes[c*b]=0; will fail if c*b == howmany.
Last edited on
rozick1 (218)
Ah great thanks.
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