小码哥Swift技术学习(day04--流程控制)

一、if-else

let age = 4
if age >= 22 {
    print("Get married")
} else if age >= 18{
    print("Being a adult")
} else if age >= 7 {
    print("Go to school")
} else {
    print("Just a child")
}

1.if后面的条件可以省略小括号

2.条件后面的大括号不可以省略

3.if后面的条件只能是Bool类型（以前0是假，非0是真，现在不能用整型数字）

二、while

var num = 5
while num > 0 {
    print("num is \(num)")
    // 5 4 3 2 1
    num -= 1
}

三、repeat-while

var num1 = -1
repeat {
    print("num is \(num1)")
} while num1 > 0

1.repeat-while相当于C语言中的do-whlie

2.从Swift3开始，去除了自增（++）、自减（--）运算符

四、for

1.闭区间运算符：a...b, a <= 取值 <= b

let names = ["Anna","Alex","Brian","Jack"]
for i in 0...3 {
    print(names[i])
}

let range = 1...3
for i in range {
    print(names[i])
}

let a = 1
let b = 2
for i in a...b {
    print(names[i])
}

for i in a...3 {
    print(names[i])
}

2.i默认是let，有需要可以声明为var

for var i in 1...3 {
    i += 5
    print(i)
}

3. 如果i用不到，可以写成下划线_

for _ in 1...3 {
    print("123")
}

4.半开区间运算符：a..<b，a <= 取值 <b

for i in 1..<5 {
    print(i)
}

5.for--区间运算符用在数组上

for name in names[0...3] {
    print(name)
}

6.单侧区间---让区间朝同一个方向尽可能的远

如果对于数组来说就是有范围的远，如果剥离了数组，那么就是没有范围

for name in names[2...] {
    print(name)
}

for name in names[...2] {
    // 0...2
    print(name)
}

for name in names[..<2] {
    // 0,1
    print(name)
}

let range1 = ...5
print(range1.contains(7))
print(range1.contains(4))
print(range1.contains(-3))

五、区间类型

1.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" //区间类型为CloseRange<String>
print(stringRange1.contains("cb"))
print(stringRange1.contains("dz"))
print(stringRange1.contains("fg"))

let stringRange2 = "a"..."f"
print(stringRange2.contains("d"))
print(stringRange2.contains("h"))

2.字符也用双引号来写，双引号默认是字符串，如果是字符的话，需要用到Character来修饰

// "a"默认是字符串，如果是字符的话需要:Character
// \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"))

3.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)
}

六、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
}

1.case、default后面不能写{}

2.默认可以不写break，不会贯穿到后面的条件

var number1 = 2
switch number1 {
case 1:
    print("number is 1")
case 2:
    print("number is 2")
default:
    print("number is other")
}

3.使用fallthrough可以实现贯穿效果

var number2 = 1
switch number2 {
case 1:
    print("number2 is 1")
    fallthrough
case 2:
    print("number2 is 2")
default:
    print("number2 is other")
}

4.switch必须要保证能处理所有情况

5.case、default后面至少要有一条语句，如果不想做任何事情，加个break即可

var number4 = 1
switch number4 {
case 1:
    print("number is 1")
case 2:
    print("number is 2")
default:
    break
}

6.如果能保证已处理所有情况，也可以不必使用default

// 如果能保证已处理所有情况，也可以不必使用default
enum Answer {
    case right
    case wrong
}

let answer = Answer.right
switch answer {
case Answer.right:
    print("right")
case Answer.wrong:
    print("wrong")
}

// 由于已确定answer是Answer类型，因此可以省略Answer
switch answer {
case .right:
    print("right")
case .wrong:
    print("wrong")
}

上面只有两种类型，可以不写default

7.复合条件

switch也支持Character、String类型

// 希望当stringName无论是"Jack"还是"Rose“的时候都打印Right person
let stringName = "Jack"
switch stringName {
case "Jack":
    fallthrough
case "Rose":
    print("Right person")
default:
    break
}

switch stringName {
case "Jack", "Rose":
    print("Right Person")
default:
    break
}

let character: Character = "a"
switch character {
case "a","A":
    print("The letter A")
default:
    print("Not the letter A")
}

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七、区间匹配、元组匹配

1.区间匹配，判断定义的值是否在某一个区间

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")
    
}

2.元组匹配

元组中的两个值是否都在两个元组中，如果是_的话说明没有限制

2.1 可以使用下划线_忽略某个值

2.2 关于case匹配问题，属于模式匹配(Pattern Matching)的范畴

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")
}

八、值绑定

1.值绑定看是否有值相同，有一个相同的值就进行哪一个选择，然后将那个值赋值给case里面的值

2.必要时let也可以改为var

let point1 = (2, 0)
switch point1 {
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 a y value of \(y)")
case let(x, y):
    print("somewhere else at (\(x), \(y)")
}

九、where

where是用来进行筛选条件的

let point2 = (1, -1)
switch point2 {
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 arbitrary point")
}

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)

十、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)")
}
}

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