区间运算符可以用来表示两个操作数之间的范围集合。 1，闭区间运算符：a…b for iCount in 512...1024{

//从512遍历到1024（包括1024）

} 2，半闭区间运算符：a..<b var fruts = ["apple","orange","banana"]

let iCount = fruts.count

for i in 0..<iCount{

print("第\(i+1)个水果是\(fruts[i])")

} 3，倒序循环 通过 reversed() 方法，我们可以将一个正序循环变成逆序循环。

for i in (0..<10).reversed() {

print(i)

} 4，字符串范围也可以使用区间运算符 //字符串截取

let words = "Hangge.com"

//不使用区间运算符

let index = words.index(words.startIndex, offsetBy: 4)

let index2 = words.index(words.startIndex, offsetBy: 6)

let range1 = Range(uncheckedBounds: (lower: index, upper: index2))

let rangeStr1 = words.substring(with: range1) //ge

print(rangeStr1)

//使用区间运算符

let range2 = words.index(words.startIndex, offsetBy: 4)..<words.index(words.startIndex,

offsetBy: 6)

let rangeStr2 = words.substring(with: range2) //ge

print(rangeStr2) 5，区间运算符除了返回一个Range外，还可以接受Comparable的输入，返回ClosedInterval或HalfOpenInterval 所以我们可以用这个特性检查字符串里的字符是不是都是合法字符（比如是不是都是小写）

let words = "Hangge.com"

let interval = "a"..."z"

for c in words.characters {

if !interval.contains(String(c)){

print("\(c)不是小写字母")

}

}

//H不是小写字母

//.不是小写字母