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.

Running time: Unknown

Assessment: First code I’d written in 7-8 years. I hadn’t started measuring execution time yet, so I’m not sure how long it took to run, but it’s basically instantaneous.

#include <iostream>
using namespace std;

int main()
{
	int total = 0;
	for (int i = 0; i < 1000; i++)
	{
		if( (i % 3 == 0) || (i % 5 == 0) )
			total += i;
	}
	cout << total;	
	return 0;
}