Project Euler - Problem 10 - Summation of primes

p10_projecteuler.cpp

/*
Project_10.cpp : Summation of primes
The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.
Find the sum of all the primes below two million.
*/

#include <iostream>
using namespace std;

int main()
{
  long long sum = 0;  // long long data type as sum will be too big, starts from 2
  bool prime = true;
  for(int i=3; i<2000000; i+=2){  // until 2 million
    prime = true;     // set prime true, if not it will change
    for(int j=2; j<=(i/2); j++){    // until half of the number
      if (i % j == 0) {         // check if not prime
        prime = false;      // set prime false so that it won't add to sum
      }
    }
    if(prime){          // if i is prime
      sum = sum + i;    // add it to sum
      // cout << "Sum: " << sum << endl;  // if you want to print sum everytime it finds prime
    }
  }
  cout << "Sum: " << sum << '\n';   // print the final sum

  return 0;
}

// Answer is: 142913828922
// it's really long to find the answer...