字符串拼接

let str1 = "Hello"
let str2 = " World!"
let str3 = str1 + str2

字符串格式化

格式化

let str1 = String(1)        // 1
let str2 = String(2.0)      // 2.0 let str3 = str1 + str2      // 12.0

保留两位小数

// 5本书的价格共计： ¥110.23
let str4 = String(format: "%d本书的价格共计： ¥%.2f", 5, 110.23456)         

不足两位前面补0

let str5 = String(format: "%02d", 1)        // 01
let str6 = String(format: "%02d", 11)       // 11

获取字符串长度

let str1 = "string"
print(str1.count)    // 6

遍历字符串

let str1 = "string"
for char in str1 {
    print(char)
}

字符串操作

获取首字符

let str = "Hello"
let str1 = str[str.startIndex]      // H

删除首字符

var str2 = "Hello2"
str2.removeFirst()
print(str2)            // ello2

删除指定位置

var str3 = "ABCDabcd"
str3.remove(at: str3.index(str3.startIndex, offsetBy: 2))
print(str3)            // ABDabcd

删除最后一个字符

var str4 = "ABCD"
str4.removeLast()
print(str4)            // ABC

删除所有内容

var str5 = "ABCD"
str5.removeAll()

删除头尾指定位数内容

var str6 = "ABCDabcd"
str6.removeFirst(2)
print(str6)            // CDabcd
str6.removeLast(2)
print(str6)            // CDab

删除某段内容

var str7 = "ABCDabcd"
let startIndex = str7.index(str7.startIndex, offsetBy: 2)
let endIndex = str7.index(str7.endIndex, offsetBy: -2)
str7.removeSubrange(startIndex ... endIndex)
print(str7)             // ABd

首字母大写

var str8 = "abcdefg".capitalized
print(str8)             // Abcdefg

判断字符串是否包含另一个字符串

let str1 = "Hello"
let str2 = "Hello World"
let result = str2.contains(str1)
print(result)         // 输出：true

字符串转数组

let str1 = "Hello World 123"
let array = str1.split(separator: " ")
print(array)         // 输出：["Hello", "World", "123"]

数组转字符串

let array1 = ["Aa", "Bb", "Cc"]
let str1 = array1.joined()
print(str1)         // 输出：AaBbCc
let str2 = array1.joined(separator: "-")
print(str2)         // 输出：Aa-Bb-Cc

字符串截取

头部截取

let str = "abcdefgABCDEFG"
let str1 = str.prefix(2)
print(str1)     // ab

尾部截取

let str2 = str.suffix(3)
print(str2)     // EFG

range 截取

let indexStart = str.index(str.startIndex, offsetBy: 2)
let indexEnd = str.index(str.startIndex, offsetBy: 10)
let indexStr = str[indexStart ... indexEnd]
print(indexStr)     // cdefgABCD

截取指定位置字符串

let range = str.range(of: "AB")
print(str[str.startIndex ..< range!.lowerBound])  // abcdefg
print(str[str.startIndex ..< range!.upperBound])  // abcdefgAB

字符串替换

let str1 = "ABCDabcd"
let str2 = str1.replacingOccurrences(of: "AB", with: "ab")
print(str2)    // abCDabcd

字符串插入

var str1 = "ABCDabcd"

// 单个字符
str1.insert("新", at: str1.index(str1.startIndex, offsetBy: 2))
print(str1)      // AB新CDabcd

// 多个字符
var str2 = "ABCDabcd"
str2.insert(contentsOf: "新来的", at: str2.index(before: str2.endIndex))
print(str2)     // ABCDabc新来的d