Euler1

//If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9.
//The sum of these multiples is 23.
//Find the sum of all the multiples of 3 or 5 below 1000. (1000 not included)

#include <iostream>
using namespace std;

bool multipleOf3(int x)
{
    int factor_3 = x / 3;
    if (factor_3*3 == x) return true;
    else return false;
        // can also use if (x % 3 == 0) to find if x is a multiple of 3
}

bool multipleOf5(int y)
{
    int factor_5 = y / 5;
    if (factor_5 * 5 == y) return true;
    else return false;
}

int main()
{
    int i = 1;
    unsigned long int sum = 0;
    while (i < 1000)
    {
        if ((multipleOf3(i) == true) || (multipleOf5(i) == true)) sum += i;
        i++;
    }
    cout << sum << endl;
    system("pause");
    return 0;
}