// MARK: - 字符串长度
    func demo5() {
        let string = "hello world"
        
        // 1，字符串的遍历,字符串是一个结构体
        for c in string.characters {
            print(c)
        }
        // 2， 返回指定编码对应的的字节数量
        //        utf8 编码（0-4）个，每个汉字的是3个字节
        print(string.lengthOfBytes(using: .utf8))
        
        // 3， 字符串长度--- 获取字符的个数
        print("---\(string.characters.count)----")
        
        // 4，使用NSString中转 ( string as  "类型"  swift中的类型转换)
        let ocString = string as NSString
        print(ocString.length)
    }

// MARK: - 字符串的拼接
    func demo6()  {
        
        let name = "谁家娇妻守空房"
        let age = "隔壁老王来帮忙"
        let title:  String? = "大王叫我来巡山了"
        
        let nameString  = "\(name) \(age) \(title ?? "")"
        print(nameString)
        print(name + age + (title ?? ""))
    }

// MARK: - 字符串的截取
    func demo8() -> () {
        let titleString = "曾经的王者,如今的小弟"
        
        // 1，转化成NSString ，强烈建议使用
        let ocString = titleString as NSString
        
        let string1 = ocString.substring(with: NSMakeRange(2,4))
        print(string1)
        
        // 2，swift 3.0以后的新方法
        
        // from："字符串的起始长度"
        let string2 = titleString.substring(from: "我们".endIndex)
        let string3 = titleString.substring(from: "adc".endIndex)
        
        print("-------------")
        print(string2)
        print(string3)
        
        // 字符串的范围
        guard  let range = titleString.range(of: "王者") else {
            print("不包括字符串")
            return
        }
        print("------------")
        print(range) // 获取字符串对应的 range
        print(titleString.substring(with: range))
        
    }

// MARK: - 特定格式化字符串
    func demo7() -> () {
        let h = 7
        let m = 30
        let s = 0
    
        print("\(h):\(m):\(s)")
    
        let dataString  = String(format: "%02d:%02d:%02d",h,m,s)
        print(dataString)
    }