參見：Implicit conversions

摘錄：

Real floating-integer conversionsA finite value of any real floating type can be implicitly converted to any integer type. Except where covered by boolean conversion above, the rules are: The fractional part is discarded (truncated towards zero). If the resulting value can be represented by the target type, that value is used otherwise, the behavior is undefined

翻譯：

浮點型轉化為整型（除了_Bool型別。轉化為_Bool時沒有向0取整的過程，而是直接比較其是不是0）的規則是：

先向零取整，如果取整後的結果能被目標整型容納，那一切OK；若不能，則屬於未定義行為。