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！

//1.指定位置插入字符串

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

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

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

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

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

//指定删除字符串

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

string.removeSubrange(range0!)

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

////打印count 值，结果为： 21

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

//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

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

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)

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

//4.以某一特定位置来截取字符串

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

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

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

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

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

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

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

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

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

//5.字符串替换

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

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

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

//6.字符串转数组

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

//7.数组转字符串

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

print("strItem: \(strItem)")