Multiples of 3 and 5#

#include<bits/stdc++.h>

int main() {
  int sum = 0;
  for (int i = 1 ; i < 1000 ; i++) {
    if (i % 3 == 0 || i % 5 == 0) {
      sum += i;
    }
  }

  printf("%d\n", sum);
  return 0;
}

OUTPUT

233168