Find the sum of all the multiples of 3 or 5 below 1000

Question

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. I have the following code but the answer do

Answer 1

You might start by iterating from 3 to 1000 in steps of 3 (3,6,9,12,etc), adding them to the sum like,

int i = 3, sum = 0;
for (; i < 1000; i += 3) {
  sum += i;
}

Then you could iterate from 5 to 1000 by 5 (skipping multiples of 3 since they've already been added) adding those values to the sum as well

for (i = 5; i < 1000; i += 5) {
  if (i % 3 != 0) sum += i;
}

Then display the sum

printf("%d\n", sum);