Depending on the compiler, you may actually be passing a double value instead of a float. Try using the "f" on the end of your call.
add(10.2f, 60.1f)
I think (trying to go from memory here) that a double can be cast to both a float and an int but must be done explicitly. Without telling it which one to use, the compiler can't choose for you since they are both narrowing conversions (lose data) and it tells you to pick one yourself.