In case of casting a float/double value to int, you generally loose the fractional part due to integer truncation.
This is quite different from rounding as we would usually expect, so for instance 2.8 ends up as 2 with integer truncation, just as 2.1 would end up as 2.
Update:
Another source of potential (gross) inaccuracy with casting is due to the limited range of values being able to be represented with integers as opposed to with floating point types (thanks to @R reminding us about this in the comment below)