为什么我的代码无法正确生成素数

Question

The number of prime numbers less than 10,000,000 is 664,579 but my code generates only 664,214. The source of the numbers is https://primes.utm.edu/howmany.html

#include <iostream>
#include <bitset>
#include <vector>
using namespace std;

const int N = 10000001;
bitset<N>num;
vector<int>prime;
inline void sieve()
{
    num.flip();
    num[0] = num[1] = 0;
    for(int i=2;i<N;i++)
        if(num[i])
        {
            prime.push_back(i);
            for(long long unsigned j=i*i; j<N;j+=i)
                num[j] = 0;
        }
}

int main() {
    sieve();
    cout << prime.size() << endl;
    return 0;
}

Answer 1

You have an integer overflow when calculating i*i . The fact that you then assign the result to a long long doesn't make the compiler promote the types before the multiplication.

If I declare i as a long long unsigned int then your program outputs 664579