import UIKit//swift 字符串//1>swift中的字符串String是一個結構體，性能更高//2>NSString是一個OC對象，性能略差//3>String支持直接遍歷//4>Swift提供了String和NSString的無縫轉換let str = "hello world"//遍歷字符串for c in str.characters{    PRint(c)}//字符串拼接//兩個字符串之間的拼接let str1 = "你好"let str2 = "世界"let str3 = str1 + str2//字符串和其它標識符的拼接let name = "ZYF"let age = 18let height = 1.88let info = "my name is /(name) , my age is /(age) , my height is /(height)"//拼接字符串時，字符串的格式化let minent = 2let seconds = 8let timeString = String(format: "%02d:%02d", arguments:[minent,seconds])print(timeString)//字符串的截取let urlStr = "www.zhengyanfeng.com"//將String類型轉換為NSString類型let header = (urlStr as NSString).substring(to: 3)let body = (urlStr as NSString).substring(with: NSRange(location: 4, length: 12))let afterbody = (urlStr as NSString).substring(from: 17)