I assume you are doing Project Euler 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.
There are a couple problems with your algorithm. you are setting f to 200 and t to 333. then you decrement both, so eventually, you will get to f at 0, and t at 133. your condition will fail, and so you will have missed many of the multiples of 3.
But additionally, you are also adding in some factors twice. 600, for example, is a multiple of BOTH 3 and 5, and your current method will add it in twice.
One thing I often do when working on these problems (and i've done the first 60 or so) is to
test my algorithm against the smaller case. You know what the answer should be for using 10 instead of 1000. Change your code on lines 14 and 15 to use 10, and see if you get the right answer.
Another thing you can do is to print the values your adding in each time - so after line 22 print out totalFive and after line 24 print totalThree. By setting your original limit to 10, you can see if a) you are getting everything you should, and b) that you are not counting any values twice.