let age = 4if 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")}
2.whileif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
var num = 5while num > 0 { print("num is (num)")num -= 1 } // 打印了5次
repeat-whilerepeat-while相当于C语言中的do-while
var num = 1repeat { print("num is (num)") } while num > 0 // 打印了1次
for 2.1.闭区间运算符:a…b， a <= 取值 <= blet names = ["Anna", "Alex", "Brian", "Jack"]for i in 0...3 { print(names[i])} // Anna Alex Brian Jack
保存区间范围let range = 1...3for i in range { print(names[i])} // Alex Brian Jack
变量作为区间let a = 1var b = 2for i in a...b { print(names[i])} // Alex Brian
i默认是let，i需要改变时可以声明为varfor var i in 1...3 {i += 5 print(i)} // 6 7 8
不需要i时省略for _ in 1...3 { print("for")} // 打印了3次
2.2.半开区间运算符:a…for name in names[2...] { print(name)} // Brian Jack
2.4.for – 区间运算符用在数组上for name in names[0...3] { print(name)} // Anna Alex Brian Jack
2.5.区间是否包含let range = ...5range.contains(7) // falserange.contains(4) // truerange.contains(-3) // true
2.6.带间隔的区间值let hours = 11let hourInterval = 2// tickMark的取值:从4开始，累加2，不超过11for tickMark in stride(from: 4, through: hours, by: hourInterval) { print(tickMark)} // 4 6 8 10
3.switchvar number = 1switch number {case 1: print("number is 1")case 2: print("number is 2")default: print("number is other")} // number is 1
3.2fallthrough默认可以不写break，并不会贯穿到后面的条件
case、default后面不能写大括号{}
var number = 1switch number {case 1: print("number is 1") fallthroughcase 2: print("number is 2")default: print("number is other")}// number is 1// number is 2
3.3switch注意点3.4区间匹配、元组匹配switch必须要保证能处理所有情况
如果能保证已处理所有情况，也可以不必使用default
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
switch也支持Character、String类型
区间匹配
let count = 62switch 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 the box
值绑定 对于元组来说，只要符合那么就会赋值到case的元组中的变量中（变量可以符合任意的值）。
必要时let也可以改为var
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 a y value of (y)")case let (x, y): print("somewhere else at ((x), (y))")} // on the x-axis with an x value of 2
4.where（条件过滤）满足条件才会执行。
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 arbitrary point")} // on the line x == -y
// 将所有正数加起来var numbers = [10, 20, -10, -20, 30, -30]var sum = 0for num in numbers where num > 0 { // 使用where来过滤numsum += num }print(sum) // 60
5.标签语句在指定的标签位置继续执行或者结束执行
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)") }}