/**

字符串的构造

*/

let str1 = "hello"

let str2 = "world"

// 拼接 没有减号哦

let str3 = str1 + str2

print(str3)

let index = 9

let urlHead = "http://www.mobiletrain.org/"

let message = "\(urlHead)/pic/\(index).png"

print(message)