Swift 语言主要使用 String 和 Character 来存储字符数据。String 是字符串类型，Character 是字符类型，一个或多个字符组成一个字符串，不多说了，直接上代码！

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//1.指定位置插入字符串

var string = "https:www.baidu.com"

let index = string.index(string.startIndex, offsetBy: 6)

string.insert(contentsOf: "//".characters, at: index)

//结果为：https://www.baidu.com

print("string of : \(string)")

string.insert("!", at: string.endIndex)//末尾加！

//结果为：  https://www.baidu.com!

print("string end: \(string)")

//指定删除字符串

var string = " https://www.baidu.com"

let range0 = string.range(of: "!")

string.removeSubrange(range0!)

//结果为：https://www.baidu.com

print("remove string: \(string)")

////打印count 值，结果为： 21

print("string count : \(string.characters.count)")

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//2.指定index 的位置是以后面开始，向左移动3位开始截取字符串

var string = " https://www.baidu.com"

let index1 = string.index(string.endIndex, offsetBy: -3)

//截取以index 的位置的字符串

let fromIndex = string.substring(from: index1)

//结果为： com

print("sub from string : \(fromIndex)")

//3.制定index 的位置是以前面开始，向右移动5位开始截取字符串

var string = " https://www.baidu.com"

let index2 = string.index(string.startIndex, offsetBy: 5)

//截取以index 的位置的字符串

let toIndex = string.substring(to: index2)

//结果为： https

print("sub to string : \(toIndex)")

//4.以某一特定位置来截取字符串

var string = " https://www.baidu.com"

let range = string.range(of: "baidu")

let lowerStr = string.substring(to: (range?.lowerBound)!)

//结果为： https://www.

print("to lower string: \(lowerStr)")

let upperStr = string.substring(to: (range?.upperBound)!)

//结果为： https://www.baidu

print("to upper string: \(upperStr)")

let lowerStr2 = string.substring(from: (range?.lowerBound)!)

//结果为： baidu.com

print("from lower string: \(lowerStr2)")

let upperStr2 = string.substring(from: (range?.upperBound)!)

//结果为： .com

print("from upper string: \(upperStr2)")

//5.字符串替换

var string = " https://www.baidu.com"

let range1 = string.range(of: "baidu")

string.replaceSubrange(range1!, with: "google".characters)

//结果为：https://www.google.com

print("replace string :\(string)")

//6.字符串转数组

var string = " https://www.baidu.com"

let arr = string.components(separatedBy: ".")

//结果为： ["https://www", "google", "com"]

print("arr item : \(arr)")

//7.数组转字符串

var string = " https://www.baidu.com"

let strItem = arr.joined(separator: "#")

//结果为：https://www#google#com

print("strItem: \(strItem)")