I'm making a program that is supposed to get the sum of all prime number in a specified range which is in this case 1 000 000. The program works fine, except that it seems to count some prime numbers even if they aren't prime.

Here is my code:

I'm fairly certain that the isPrime() function is wrong, since the actual prime count should be somewhere closer to 78000. My program counts exactly: 78665 when the range is 1 000 000. It works fine when I take a lower range. Any ideas/improvements?Code:#include <iostream> #include <cmath> using namespace std; const int RANGE = 1000000; bool isPrime(int n) { if (n <= 0 || n == 1 || (n % 2 == 0 && n != 2)) return false; for (int i=3;i<sqrt(n);i++) { if ((n%i) == 0) return false; } return true; } int main(void) { unsigned long sumPrimes = 0; long counter = 0; for (int i=0;i<RANGE-1;i++) { if (isPrime(i)) { cout << i << endl; sumPrimes+=i; counter++; } } cout << "Counter: " << counter << endl; cout << "Sum of primes: " << sumPrimes; while (cin) cin.get(); return 0; }