//  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 == "),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:""),str4)
        
        //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 == "),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 = ",banana"
        var ss3 = ss1+ss2
        if ss1 == ss2 {
            print("ss1=ss2")
        }
        if ss1+ss2 == ss3 {
            print("ss1+ss2=ss3")
        }
        if 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: ",")!))//,banana 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
        print(ss3)// hellobanana
        
    }