why is there a segmentation fault on large number inputs e.g.. 1000000?

Question

This is the solution to this question https://practice.geeksforgeeks.org/problems/sum-of-all-prime-numbers-between-1-and-n/0

method :

1. used sieve of eratosthenes to find all the numbers from 1 to N(input) .
2. Created an array s that stores the sum of all prime numbers from 1 to i(index of array). after taking in input: test cases and the values stored in an array ...
3. selects the max N out of all test cases..calls the sieve function that finds the sum of all prime no.s till max N.
4. The input array is traversed and the corresponding sum outputs are displayed.

this works for small values of N but for larger inputs it gives a set fault !

#include <iostream>
using namespace std;


void sieve(int s[], int n)
{
    int *a = new int[n + 1];
    for(int i = 0; i < n + 1; ++i)
        a[i] = 1;

    for(int i = 2; i < n + 1; ++i)
    {
        if(a[i])
        {
            int x;
            for(int j = 0; x = i * (i + j), x < n + 1; ++j)
            {
                a[x] = 0;
            }
        }
    }
    int sum = 0;
    for(int i = 2; i < n + 1; ++i)
    {
        // cout << a[i] << " ";

        if(a[i])
            sum += i;
        s[i] = sum;
    }
    //cout << endl;
    s[0] = s[1] = 0;
    /*for(int i = 2; i < n + 1; ++i)
    {
        cout << s[i] << " ";
    }
    cout << endl;*/
}

int main() {
    //code

    int t;
    cin >> t;
    int a[t];
    for(int i = 0; i < t; ++i)
    {
        cin >> a[i];
    }

    int max = a[0];

    for(int i = 1; i < t; ++i)
    {
        if(a[i] > max)
        {
            max = a[i];
        }
    }

    int s[max+1];

    sieve(s, max);

    for(int i = 0; i < t; ++i)
    {
        cout << s[a[i]] << endl;
    }

    return 0;
}

PS. sorry for the lack of comments..was in a hurry :P