字符串的构造

字符串拼接

let str1 = "hello"
let str2 = "world"
let str = str1 + str2
print(str)

格式化字符串

var index = 9
var urlhead = "http://www.mobiletrain.org"
let message = "\(urlhead)/pic/\(index).png"
print(message)

字符串的比较

let str22 = "hello"
if str == "hello" {
    print(str)
}

if str >= "hello" {
    print(str)
}

前缀/后缀

let str33 = "apple"
//    前缀
if str33.hasPrefix("le") {
    print("前缀\(str33)")
//    后缀
} else if str33.hasSuffix("le") {
    print("后缀\(str33)")
}

大小写转换

let str44 = "apple"
let str55 = "APPLE"
print("小写转大写\(str44.uppercased())")
print("大写转小写\(str55.lowercased())")

字符串长度

print("tingPS.characters.count")

更细致的内容请看
Swift3.0 中 Strings/Characters 闲聊