Problem
https://projecteuler.net/problem=1
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.
Answer: 233168
Solution
#include <iostream>
int sum_natural_35(size_t upper)
{
unsigned int sum(0);
for( int i = upper ; --i; )
{
if( 0 == i % 3 )
{
sum += i;
}
else if ( 0 == i % 5 )
{
sum += i;
}
}
return sum;
}
int main(int argc, char* argv[])
{
std::cout << sum_natural_35(1000) << std::endl;
}