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String 的原因
String 是一个结构体，性能更高NSString 是一个 OC 对象，性能略差String 支持直接遍历Swift 提供了 String 和 NSString 之间的无缝转换// 字符串遍历
var str = "Hello, Swift"
for c in str.characters {
print(c)
}
let str1 = "Hello"
let str2 = "World"
let str3 = str1 + str2
let name = "why"
let age = 18
let info = "my name is \(name), age is \(age)"
let min = 3
let second = 4
let time = String(format: "%02d:%02d", arguments: [min, second])
import UIKit // 1.定义字符串：swift定义字符串不用加@，直接是c语言字符串“” let str = "hello world" // 2.遍历字符串中字符：空格也算是一个字符 for c in str.characters { print(c) } // 3.字符串的拼接 // 3.1.字符串之间的拼接 let str1 = "小码哥" let str2 = "IT教育" let result = str1 + str2 // 3.2.字符串和其他标识符之间的拼接 let age = 18 let name = "why" let height = 1.88 // 拼接其他标识符的格式: \(标识符的名称) let info = "my name is \(name), age is \(age), height is \(height)" // 3.3.字符串的格式化: %02d表示占位的意思，占两位，不足两位的用0去补位，arguments参数类型为一个数组，[min, second]表示一个数组，swift数组中可存放基本类型数据，用[]来表示 //音乐播放器： let min = 3 let second = 04 let timeStr = String(format: "%02d:%02d", arguments: [min, second]) // 4.字符串的截取：from 和 to都包括了 let urlString = "www.520it.com" // 将String类型转成NSString类型 string as NSString let header = (urlString as NSString).substring(to: 3) let middle = (urlString as NSString).substring(with: NSRange(location: 4, length: 5)) let footer = (urlString as NSString).substring(from: 10)
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原文地址：http://www.cnblogs.com/cqb-learner/p/5883316.html
