Finish the solution so that it returns the sum of all the multiples of 3 or 5 BELOW the number passed in.

and

Note: If the number is a multiple of both 3 and 5, ONLY COUNT IT ONCE.

3 + 5 + 6 + 9 + 10 + 12 + 15 + 18 = 78

The sample test has problem for number = 20.

It should equal 93 while it is 78 now!

Which language? Please when you have troubles with a kata that has several (like this one), state it. Also provide more information, nobody can help you with only that.

Exactly! So, i will take it into account while nominating for Best Performance next time...
Be Prepared! (chuckle)
Though i did not see any calls in your C solution nor any iterations...
(*)

When I pressed the run sample test, I passed, but when I attempted the same code, I failed the same sample test? Also, the "random number" isnot so random