Swift 字符串转换 字符串拼接 字符串遍历 字符串方法

import UIKit

var str:String = "Hello, playground"
str = ""
//通过构造方法来进行str变量的构造
str = String()              //构造空字符串      ""
str = String("hello")       //通过字符串构造     "hello"
str = String(666)           //通过整型数据构造    "666"
str = String(6.66)          //通过浮点型数据构造  "6.66"
str = String("a")           //通过字符构造       "a"
str = String(false)         //通过Bool值构造     "false"
str = String(describing: (1,1.0,true))  //通过元组构造       "(1,1.0,true)"
str = String(describing: [1, 2, 3])     //通过列表构造       "[1, 2, 3]"
str = String(format:"我是%@","珲少") //通过格式化字符串构造 "我是珲少"
str = String(describing: Int.self)           //通过类型来构造字符串 "Int"

var a = Int(1.05)     //将1.05 转成1
var b = Float(a)      //通过整型数据a构造浮点型数据b

//字符串的组合
var c1 = "Hello"
var c2 = "World"
var c3 = c1+" "+c2  //"Hello World"
//使用\()进行字符串插值
var d = "Hello \(123)"      //"Hello 123"
var d2 = "Hello \(c2)"      //"Hello World"
var d3 = "Hello \(1+2)"      //"Hello3"

MemoryLayout<String>.size // 16
MemoryLayout<Character>.size // 16

//创建一个字符
var e:Character = "a"
//创建字符数组
var e2 : [Character] = ["H","E","L","L","O"]
//通过字符数组来构造字符串 "HELLO"
var e3 = String(e2)
//通过构造方法来创建字符类型变量
var e4 = Character("a")
//进行for-in遍历
let name = "China"
for character in name {
    print(character)
}
//使用unicode码来创建字符  21为!
"\u{21}"

//判断字符串是否为空
var obj1 = ""
if obj1.isEmpty {
    print("字符串为空字符串")
}
//获取字符串中字符个数
obj1.count

var com1 = "30a"
var com2 = "31a"
//比较两个字符串是否相等 只有两个字符串中的所有位置的字符都相等时 才为相等的字符串
com1==com2
//比较两个字符串的大小
com1<com2


var string = "Hello-Swift"
//获取字符串首个字符的下标  0位置
var startIndex = string.startIndex
//获取最后一个字符的下标  11位置
var endIndex = string.endIndex
//获取某个下标后一个下标对应的字符 char="e"
var char = string[string.index(after: startIndex)]
//获取某个下标前一个下标对应的字符 char2 = "t"
var char2 = string[string.index(before: string.endIndex)]
//通过范围获取字符串中的一个子串 Hello
var subString = string[startIndex...string.index(startIndex, offsetBy: 4)]
var subString2 = string[string.index(endIndex, offsetBy: -5)..<endIndex]
//追加一个字符 此时 string = "Hello-Swfit!"
string.append(Character("!"))
//获取某个子串在父串中的范围
var range = string.range(of: "Hello")
//追加字符串操作 此时string = "Hello-Swift! Hello-World"
string.append(" Hello-World")
//在指定位置插入一个字符 此时string = "Hello-Swift!~ Hello-World"
string.insert("~", at: string.index(string.startIndex, offsetBy: 12))
//在指定位置插入一组字符 此时string = "Hello-Swift!~~~~ Hello-World"
string.insert(contentsOf: ["~","~","~"], at: string.index(string.startIndex, offsetBy: 12))
//在指定范围替换一个字符串 此时string = "Hi-Swift!~~~~ Hello-World"
string.replaceSubrange(string.startIndex...string.index(string.startIndex, offsetBy: 4), with: "Hi")
//在指定位置删除一个字符 此时string = "Hi-Swift!~~~~ Hello-Worl"
string.remove(at: string.index(before:string.endIndex))
//删除指定范围的字符 此时string = "Swift!~~~~ Hello-Worl"
string.removeSubrange(string.startIndex...string.index(string.startIndex, offsetBy: 2))
//删除所有字符  此时string = ""
string.removeAll()

var string2 = "My name is Jaki"
//全部转换为大写
string2 = string2.uppercased()
//全部转换为小写
string2 = string2.lowercased()
//检查字符串是否有My前缀
string2.hasPrefix("My")
//检查字符串是否有jaki后缀
string2.hasSuffix("jaki")