【Swift4】(2) 运算符 | 字符串

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基于版本：4.1.2

运算符

• 赋值

let a = 2

• 操作符

a + b
a += a //swift4 废弃++
a +=2

a * b
a / b //b不能为0
a % b // b 不能为0

let d = 5.2,e = 1.7
d / e
d % e //也能使用浮点型进行求余

Int.max //查看Int类型支持的最大值
Int.min //查看Int类型支持的最小值

var c = 2
c+=1

//条件运算符
var score = 62
var rate = score > 60 ? "合格":"不合格"

• nil聚合运算符

var userNickName :String?

userNickName = "imagine"

let outputName:String = userNickName != nil ? userNickName! : "Guest"
print("hello,"+outputName)

//改进
let outputName:String = userNickName ?? "Guest"

• 区间运算符

//闭区间 [a,b]  表示：a...b
//前闭后开区间 [a,b) 表示：a..<b

• for-in

for index in 1..<10
{
	index
	//index = 3 //error
}
//arr.count数组长度
let names = ["aaa","bbb","ccc"];
for i in 0..<names.count
{
	names[i]
}

• 逻辑运算符

!a //非
a && b //与
a || b //或

区别“位运算符”
a & b  //按位与
a | b  //按位或

字符串

• String和Character

//变量与常量字符串
var str1 = "aaa"
let str2 = "bbb" 

//创建空字符串
var emptyString = ""
var str2 = String() 

//字符串遍历
var str = "hello"
for c in str
{
    print(c)
}
//定义一个字符
var ch:Character = "!"
str.append(ch) //在字符串后面拼接一个字符

//字符串之间拼接
var str2 = "!!!"
str += str2 //hello!!!!

• String操作

var str = "Hello"

//拼接
str + "imagine"

str

str += "imagine"
str

//字符串插值
print("123 \(str)")

//字符串比较

//按字典顺序比较，不考虑长度
let str_a = "abc"
let str_b = "abc"
str_a == str_b

let str_c = "abd"
str_a < str_c

//前缀 Prefix 与 后缀 Suffix
//.hasPrefix and .hasSuffix
//统计前缀有 b 的个数
let names = [
    "a 1.aaa",
    "b 1.bbb",
    "b 2.bbb",
    "b 3.ccc"
]

var count = 0
for name in names {
    if name.hasPrefix("b"){
        count += count //3 times
    }
    
}

• 导入Foundation 使用字符串的更多功能

import Foundation

var str = "hello"
str.capitalized //Hello 首字母大写
str.uppercased() //字母大写
str.lowercased() //字母小写

//split 
var str2 = "hello hhh"

str2.components(separatedBy: " ")