c++ - Project Euler 10 exercise -

what sum of primes below 2000000? example of sum below 10 2+3+5+7 = 17

i wrote code, still getting wrong answers: tested numbers lower few hundreds, , has shown correct answers.

#include <iostream> #include <math.h> using namespace std;  bool isprime(long n) {     if (n < 2)         return false;     if (n == 2)         return true;     if (n == 3)         return true;     int k = 3;     int z = (int)(sqrt(n) + 1);     // square root n, because 1 of product must lower 6, if squared root of 36      if (n % 2 == 0)         return false;     while (n % k != 0)     {         k += 2;         if (k >= z)             return true;     }     return false; }  long primesumbelow(long x) {     long long total = 0;     (int = 0; < x; i++)         // looping times of prime appearing     {         if (isprime(i) == true)             total += i;         if (isprime(i) == false)             total += 0;     }     cout << "fd" << endl;     return total; }  int main() {     cout << primesumbelow(20) << endl;     cout << primesumbelow(2000000) << endl;      system("pause");     return 0; } 

the total counter's type correctly long long. unfortunately function primesumbelow returns long so, depending on platform, correctly calculated result truncated when it's returned function.