Note that the built-in operator != requires its operands to be of the same type, and will achieve that using promotions and conversions if necessary. In other words, your condition is equivalent to:
(float)i != (float)i
That should never fail, and so the code will eventually overflow i, giving your program Undefined Behaviour. Any behaviour is therefore possible.
To correctly check what you want to check, you should cast the result back to int:
if ((int)(float)i != i)