How to write an algorithm to find among natural numbers the sum of multiples of 3 and 5 below 1000 ?

/* This program has been worked on from http://www.s-anand.net/euler.html */

#include <stdio.h>

sofmul()
{
int n, i;
n = 0;

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

printf("Sum of the multiples of 3 and 5 below 1000 is %d \n", n);
}