玩转Swift:掌握流程控制技巧
最编程
2024-08-09 14:38:43
...
if else
.if 后面的条件可以省略小括号
.条件后面的大括号不可以省略
. if 后面的条件只能是Bool类型
let age = 4
if age >= 20 {
print("Get married");
}else if age >= 18 {
print("Being a adult")
}else if age >= 7{
print("Go to school")
}else {
print("Just a child")
}
if 条件不像OC的非零即真,一定要Boo类型
While
var num = 5
while num > 0 {
print("num is \(num)")
num -= 1
} // 打印5次
var rnum = 5
repeat {
print("rnum is \(rnum)")
rnum -= 1
} while rnum > 0 // 打印5次
.repeat while相当于C和Java中的do-whiie,循环前先执行一次
. 这里不用num --,是因为从Swift3开始,去除了自增++,自减--运算符
for
// 闭区间运算符 : a...b , a <= 取值 <= b
let names = ["Anna","Alex","Smith","Jack"]
for i in 0...3 {
print(names[i])
} //Anna Alex Smith Jack
let range = 1...3
for i in range {
print(names[i])
} // Alex Smith Jack
// i 默认是let,有需要时可以申明为var
for var i in 1...3 {
i += 5
print(i)
} // 6 7 8
省略变量
for _ in 1...3 {
print("Do Something")
} // 执行三次
// 半开区间运算符: a..b , a <= 取值 < b
for i in 1..<5 {
print(i)
} // 1 2 3 4
// for - 区间运算符用在数组上
let names = ["Anna","Alex","Smith","Jack"]
for name in names[0...3] {
print(name)
} //Anna Alex Smith Jack
// 单侧区间: 让区间朝一个方向尽可能的远
for name in names[...2] {
print(name)
} // Anna Alex Smith
for name in names[..<2] {
print(name)
} // Anna Alex
let range = ...5
print(range.contains(7)) // false
print(range.contains(4)) // true
print(range.contains(-3)) // true
区间类型
let range1: ClosedRange<Int> = 1...3
let range2: Range<Int> = 1..<3
let range3: PartialRangeThrough<Int> = ...5
字符\字符串也能使用区间运算符,但默认不能用在for-in中
let stringRange1 = "cc"..."ff"
print(stringRange1.contains("cb")) // false
print(stringRange1.contains("dz")) // true
print(stringRange1.contains("fg")) // false
\0到~囊括了所有可能要用到的ASCII字符
let characterRange: ClosedRange<Character> = "\0"..."~"
print(characterRange.contains("G")) // true
带间隔的区间值
let hours = 11
let hourInterval = 2
// tickMark的取值,从4开始,累加2,不超过11
for tickMark in stride(from: 4, through: hours, by: hourInterval){
print(tickMark)
} // 4 6 8 10
Switch
var number = 1
switch number {
case 1:
print("number is 1")
break
case 2:
print("number is 2")
break
default:
print("number is other")
break
} // number is 1
case default后面不能写打括号{}
var number = 1
switch number {
case 1:
print("number is 1")
case 2:
print("number is 2")
default:
print("number is other")
} // number is 1
默认可以不写break ,并不会贯穿到后面的条件
fallthrough可以实现贯穿效果
var number = 1
switch number {
case 1:
print("number is 1")
fallthrough
case 2:
print("number is 2")
default:
print("number is other")
}
// number is 1
// number is 2
Switch注意点
// case,default后面至少要有一条语句
// 如果不想做任何事,加个break即可
var number = 1
switch number {
case 1:
print("number is 1")
fallthrough
case 2:
print("number is 2")
default:
break
}
// 如果能保证已处理所有情况,也可以不必使用default
enum Answer {case right,wrong}
let answer = Answer.right
switch answer {
case Answer.right:
print("right")
case Answer.wrong:
print("wrong")
}
// 由于已确定的answer是Answer类型,因此可以省略Answer
enum Answer {case right,wrong}
let answer = Answer.right
switch answer {
case .right:
print("right")
case .wrong:
print("wrong")
}
复合条件
Switch也支持Character,String类型
let string = "Jack"
switch string {
case "Jack":
fallthrough
case "Rose":
print("Right person")
default:
break
} // Right person
switch string {
case "Jack","Roses":
print("Right person")
default:
break
} // Right person
let character: Character = "a"
switch character {
case "a","A":
print("The letter A")
default:
print("Not the letter A")
} // The letter A
区间匹配 元组匹配
// 区间匹配
let count = 62
switch count {
case 0:
print("none")
case 1..<5:
print("a few")
case 5..<12:
print("several")
case 12..<100:
print("dozens of")
case 100..<1000:
print("hundreds of")
default:
print("many")
} // dozens of
// 元组匹配
let point = (1,1)
switch point {
case (0,0):
print("the origin")
case (_,0):
print("on the x-axis")
case (0,_):
print("on the y-axis")
case (-2...2,-2...2):
print("inside the box")
default:
print("outside of the box")
} // inside of box
可以使用下划线_忽略某个值
关于case匹配问题,属于模式匹配(Pattern Matching)的范畴
值绑定
let point = (2,0)
switch point {
case (let x,0):
print("on the x-axis with an x value of \(x)")
case (0,let y):
print("on the y-axis with an y value of \(y)")
case let (x,y):
print("somewhere else at (\(x),\(y)")
}
// 必要时let也可以改为var
// 使用var可以修改绑定值
let point = (2,0)
switch point {
case (var x,0):
print("on the x-axis with an x value of \(x)")
x = 10 // 修改var绑定值,let修饰就不能修改
print(x)
print(point)
case (0,let y):
print("on the y-axis with an y value of \(y)")
case let (x,y):
print("somewhere else at (\(x),\(y)")
}
//on the x-axis with an x value of 2
//10
//(2, 0)
Where
let point = (1,-1)
switch point {
case let (x,y) where x == y:
print("on the line x == y")
case let (x,y) where x == -y:
print("on the line x == -y")
case let (x,y):
print("(\(x),\(y)) is just some arbitary point")
} // on the line x == -y
// 讲所有整数加起来
var numbers = [10,20,-10,-20,30,-30]
var sum = 0
for num in numbers where num > 0 { // 使用where来过滤num
sum += num
}
print(sum) // 60
标签语句
outer: for i in 1...4 {
for k in 1...4 {
if k == 3 {
continue outer
}
if i == 3 {
break outer
}
print("i == \(i),k == \(k)")
}
}
//i == 1,k == 1
//i == 1,k == 2
//i == 2,k == 1
//i == 2,k == 2
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