在OC的基础之上学习Swift：字符串String

1.OC和Swift中字符串的区别
a.在OC中字符串类型时NSString,在Swift中字符串类型是String
b.OC中字符串@"",Swift中字符串""

2.String的理解
a.String 是一个结构体，性能更高
b.NSString 是一个 OC 对象，性能略差
c.String 支持直接遍历
d.Swift 提供了 String 和 NSString 之间的无缝转换(在标识符后加:as NSString即可)

3.遍历字符串

// 1.定义字符串
let str = "hello world"
// 2.遍历字符串中字符
for c in str.characters {
    print(c)
}

4.字符串的拼接

let str1 = "小码哥"
let str2 = "IT教育"
// NSString stringwithFormat:@"%@%@", str1, str2]
let result = str1 + str2

5.字符串和其他数据类型的拼接

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)"

6.字符串的格式化

let min = 3
let second = 04
let timeStr = String(format: "%02d:%02d", arguments: [min, second])

7.字符串的截取

let urlString = "www.520it.com"

// 将String类型转成NSString类型 string as NSString
let header = (urlString as NSString).substringToIndex(3)
let middle = (urlString as NSString).substringWithRange(NSRange(location: 4, length: 5))
let footer = (urlString as NSString).substringFromIndex(10)