for(i = start; i != end; ++i)
This is the “standard” iterator loop. It has the advantage that it works with both pointers and standard library iterators (you can’t rely on iterators having operator< defined).
for(i = start; i < end; ++i)
This won’t work with standard library iterators (unless they have operator< defined), but it does have the advantage that if you go past end for some reason, it will still stop, so it’s slightly safer. I was taught to use this when iterating over integers, but I don’t know if it’s actually considered “best practice”.
The way I generally write these is to prefer <.