1.字符串拼接

var num1 = "hello,world"

var name = "xiaoming"

var  age = 18

let student = num1 + name

let info = name + String(age)

print(name + "\(age)")

2.字符串判断与比较

1??.判断是否为空

 var string1 = " "

   if string1.isEmpty {

       print("empty")

    }else{

       print("NO")

    } // 打印结果:empty

2??.比较是否相等

var string1 = "mingtianhenhao"

var string2 = "mingtianhenhao"

   if string1 ==string2{

      print("相等")

     }else{
 
       print("不相等")

     } //打印结果:相等

3??.hasPrefix 和 hasSuffix

① hasPrefix 是否以某一个字符开头

    if string1.hasPrefix("m"){ ....  }else{....}

② hasSuffix 是否以某一个字符结尾

    if string1.hasSuffix("o"){.....}else{ .... }

3.字符串遍历

 var str = "hello,world"

 str.characters.count  // 字符串的字符数(个数)

 for i in str.characters {

     print (i)

  }

4.字符串的截取

var str = "hello,world"

1??.将String转化为NSString 利用OC的方法截取

let result = (str as NSString).substringWithRange(NSMakeRange(2,3)) 
 //....打印结果 :llo

2??.利用Swift 的Range 进行截取

①获取range

// 打印:2 表示从左向右 0.1.2->  从2开始 包含2 
let start = str.startIndex.advanceBy(2) 
 
// 打印从右向左 0.9.8.7-> 从0开始 包含-1
let end  = str.endIndex.advanceBy (-1) 

let range = Range<string.index>(statr:start,end:end)

②截取

// 打印:llo,worl
let loc = str.subStringWithRange(range)  

//打印:llo,world  包含2
let statrloc = str.subStringFormIndex(statr)  

 //打印 hello,worl end的位置在字母d 那里.
let endloc = str.subStringToIndex(end)