What is Happening to my Sieve of Eratosthenes Program? - c++

Question

I'm trying to solve a challenge question of summing all primes under 2 million. Knowing full well a naive approach would take too long, I decided to implement The Sieve of Eratosthenes with a counter to record the sum. It works for up to 512500 after which I receive this error:
Is the input size just too big for code to handle? If that's the case, how can I improve my code to avoid this error. If that's not possible, what is a better algorithm to implement for these purposes?
Here is my header code:
#ifndef NUMBERSIEVE_H
#define NUMBERSIEVE_H
class NumberSieve
{
public:
NumberSieve();
virtual ~NumberSieve();
int EratosthenesSieve(int num);
private:
void SetSieve(int nums[],int Size);
int current_prime;
int current_prime_address;
void updateSieve(int nums[],int Size,int start);
bool updateCurrentPrime(int nums[],int Size,int start);
bool notComplete;
void printSieve(int nums[],int Size);
int primeSum;
};
#endif // NUMBERSIEVE_H
Here is my implementation file:
#include "NumberSieve.h"
#include <cstdlib>
#include <iostream>
NumberSieve::NumberSieve()
{
//ctor
}
NumberSieve::~NumberSieve()
{
//dtor
}
void NumberSieve::SetSieve(int nums[],int Size)
{
for(int i=0;i<Size;i++)
{
nums[i]=(i+1);
}
nums[0]=0;//Sets the first composite number 1 to 0. We use 0 as an analogy for "crossing out numbers in the Sieve".
}
void NumberSieve::updateSieve(int nums[],int Size,int start)
{
int CURRENT_PRIME=nums[start];
for(int i=start;i<Size;i++)
{
if(nums[i]%CURRENT_PRIME==0)
{
nums[i]=0;
}
}
nums[start]=CURRENT_PRIME;
}
bool NumberSieve::updateCurrentPrime(int nums[],int Size,int start)
{
for(int i=start+1;i<Size;i++)
{
if(nums[i]!=0)
{
primeSum+=nums[i];
current_prime=nums[i];
current_prime_address=i;
return true;
}
}
return false;
}
void NumberSieve::printSieve(int nums[],int Size)
{
for(int i=0;i<Size;i++)
{
std::cout<<nums[i]<<std::endl;
}
}
int NumberSieve::EratosthenesSieve(int num)
{
int Eratosthenes[num];
int primeSum=0;
SetSieve(Eratosthenes,num);
current_prime=2;
primeSum+=2;
current_prime_address=1;
updateSieve(Eratosthenes,num,current_prime_address);
notComplete=updateCurrentPrime(Eratosthenes,num,current_prime_address);
while(notComplete)
{
updateSieve(Eratosthenes,num,current_prime_address);
notComplete=updateCurrentPrime(Eratosthenes,num,current_prime_address);
}
return primeSum;
}

Answer 1

My best guess is stackoverflow, because of this:
int Eratosthenes[num];
Instead try getting it from the free store:
int* Eratosthenes = new int[num]
Update the rest of the code accordingly
If you are not comfortable with pointers, a vector might be another option.