i don't think this will work.
lets say that big only contained 10 values and top100 only contained 5, then consider this case:

bigA = {5,5,5,5,1,1,1,1,1,1,10};
then after 9 iterations top5 would looks like this: {5,5,5,5,1}
the last iteration val=10 is passed, which is bigger than the first element, and the resulting top5 will be:

{10,5,5,5,1} which is clearly not the top 5

you could solve it like this, but i think there's a big chance of a stack overflow :

1. void ReplaceSmaller(float val)
2. {
3.   for (int i = 0; i < top100.length; i++)
4.   {
5.     if (val > top100[i])
6.     {
7.       float temp = top100[i];
8.       top100[i] = val;
9.       ReplaceSmaller(temp);
10.       break; // Don't search anymore
11.     }
12.   }
13. }