Day 4 ✅ 今天做了：day4 Ja...的全部评论

取模规则a%b = a - a/b *b

前++先自增，后++先赋值

5.0/9和5/9

&& If a condition is false, it will not run (true is true) || One truth is true ! Take the opposite ^异或 不同为真