//  字符串 string
    func stringTest() -> Void {
         字符串定义
        let str1 = "yiyi"
        let str2 = 2222
        var str3 = String()空string
        var str4 = "" 空string
        
         字符定义（字符为 一 个）
        let char1:Character = d"
        
         字符串长度
        var strCount = str1.characters.count
        strCount = str1.lengthOfBytes(using: String.Encoding.utf8)
        print(String(format:strCount == ),strCount)
        
         字符串转换integer
        print((str2 as NSString).integerValue)
        
         字符串拼接
        str3 = str1 + str2
        str3 = "\(str1)\(str2)"
        str3 = globalStr + String(str1)
        print(String(format:str3 ==  字符串与字符拼接
        str4 = str1+String(char1)
        str4 = \(str1)\(char1)
        str4 = str1.appending(String(char1)) 其他类型转换string  String() exp:String(strCount)
        print(String(format:字符串与其他类型值的拼接
        let int1 = 10
        let int2 = 11.1
        let str5 = String(format:%i%.1f,int1,int2)
        print(String(format:str5 ==  字符串枚举 遍历每个字符
        let s1 = hello world!"
        if strCount != 0 {
            print(判断string长度不为0，不是空)
        }
        for c in s1.characters {
            print(c)
        }
        
         字符串比较
        let ss1 = hello
        let ss2 = 
        var ss3 = ss1+ss2
        if ss1 == ss2 {
            print(ss1=ss2if ss1+ss2 == ss3 {
            print(ss1+ss2=ss3if ss1 > ss2 { h大于b
            print(ss1>ss2 判断字符串是否包含字符串
        if (ss3 .range(of: ss1) != nil) {
            print(字符串包含子串 字符串 大小写
        print(ss3.uppercased()) HELLO,BANANA
        print(ss3.capitalized) Hello,Banana
        print(ss3.lowercased()) hello,banana
        /*
         // 这两个用法没 明白 
        print(ss3.uppercased(with: Locale(identifier: "l")))// HELLO,BANANA
        print(ss3.lowercased(with: Locale(identifier: "o")))// hello,banana
         */
        
        
         截取 修剪 字符串
        print(ss3.substring(from: ss3.characters.index(of: ")!))截取字符串从“,”开始
        print(ss3.substring(to: ss3.characters.index(of: hello 截取字符串到“,”结束
        print(ss3.unicodeScalars[ss3.unicodeScalars.startIndex ..< ss3.unicodeScalars.index(of: ")!]); hello
        print(ss3[ss3.index(ss3.startIndex,offsetBy: 4)]) o  取字符串的某个字符
        ss3.remove(at: ss3.characters.index(of: ")!) 去除字符串中特殊字符文章来自: http://www.pan5.net/ 
        print(ss3) hellobanana
        
    }