working with string

使用string

swift

In swift ,strings are squences of Unicode characters,This means that they're able to store pretty much any characters that has ever been a part of human lanuage ,which is great news for making your app translate to other lanuuages

在swift中，字符串string是采用unicode编码的字符组成的序列。这意味着string能存储几乎所有（pretty much any）组成人类语言文字(比如英语，法语，中文)的字符。这对于那些正在准备把自己的app 转成别的语言的开发者来说是一个大好消息

Creating a string in swift is easy.You can create an empty sring by creating a string literal with nothing in it:
创建一个字符串是很容易的，你可以通过一个空的双引号的方式创建一个空的字符串：

let emptyString = ""  //let 声明的是常量

还可以通过初始化字符串类型的方法创建一个空的字符串:

let anotherEmptySting = String()

用isEmpty属性来检测一个字符串是否为空：

emptyString.isEmpty  //true

要拼接字符串的话，可以用“+” 号或者是“+=” ：

var composingAString = "hello"
composingAString += ", world"   //结果为hello,world

字符串实质上是一个字符对象的序列，每个字符代表一个Unicode字符，要循环string的每一个字符的话，可以使用for-in循环

Internally a string is a squence of Character objects, each represting a Unicode character.To loop over every characters in a string, you can use a for-in loop:

var reversedString =''
for character in "hello".characters{
    reversedString =String(character) + reversedString
}
reversedString   //"olleH"    

要计算出一个string有多少个字符组成，可以使用count函数

To work out how many characters are in a string ,you use the count function:

"hello".characters.count  //5

要改变一个字符的大小写，使用uppercaseString和lowercaseString属性，它们返回原来的string被修改后的版本

To change the case of a string,you use the uppercaseString and lowercaseString properties, which return modiffed versions of the original string:

string1.uppercaseString  // 结果为HELLO
string2.lowecaseString  //结果为  hello