一、if-else 语句
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")
}
-
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
二、while循环语句
var num = 5
while num > 0 {
print("num is \(num)")
num -= 1
} // 打印5次
var num = -1
repeat {
print("num is \(num)")
}while num > 0 //打印1次
// num is -1
-
repeat-while相当于C语言中的do-while - 这里不用num-- ,因为从swift3开始,去除自增(++) 、 自减(--) 运算符
三、for循环语句
1)区间运算符: a...b 代表 a <= 取值 <= b
let name = ["Anna", "Alex", "Brian", "Jack"]
for i in 0...3 {
print(names[i])
} //Anna Alex Brian Jack
- 常量存储遍历范围
let name = ["Anna", "Alex", "Brian", "Jack"]
let range = 1...3 //CloseRang
for i in range {
print(names[i])
} //Alex Brian Jack
- 常量和变量定义取值范围
let a = 1
var b = 2
for i in a...b {
print(names[i])
} // Alex Brian
for i in a...3 {
print(names[i])
} // Alex Brian Jack
- i 默认就是let , 有需要时可以声明为var
for var i in 1...3 {
i += 5
print(i)
} // 6 7 8
- 循环中用不到 i 可以用_省略
for _ in 1...3 {
print("for")
} //打印3次
2)半开区间运算符: a...b , a <= 取值 < b
for i in 1..<5 {
print(i)
} // 1 2 3 4
3) for -区间运算符用在数组上
let names = ["Anna", "Alex", "Brian", "Jack"]
for name in names[0...3] {
print(name)
} //Anna Alex Brian Jack
- 单侧区间: 让区间朝同一个方向尽可能的远
for name in names[2...] {
print(name)
} // Brian Jack
for name in names[2...] {
print(name)
} // Brian Jack
for name in names[...2] {
print(name)
} // Anna Alex Brian
for name in names[..<2] {
print(name)
} // Anna Alex
let range = ...5
range.contains(7) //false
range.contains(4) //ture
range.contains(-2) //ture
4) 区间类型
- 闭区间类型
ClosedRange - 半开半闭区间类型
Range - 单侧区间类型
PartialRangeThrough
let range1 : ClosedRange = 1...3
let range2 : Range = 1..<3
let range3 : PartialRangeThrough = ...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" // ClosedRange
stringRange1.contains("cb") //false
stringRange1.contains("dz") //true
stringRange1.contains("fg") //false
let stringRange2 = "a"..."f"
stringRange2.contains("d") //true
stringRange2.contains("h") //false
- \0到~囊过了所有可能要用到的ASCII字符
let characterRange:ClosedRange = "\0"..."~"
characterRange.contains("G") //true
5) 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, to: hours, by: hourInterval) {
print(tickMark)
} // 4 6 8 10
四、Switch语句
1)常规用法
-
case、default后面不能写大括号
var number = 1
switch number {
case 1:
print(" ")
break
case 2:
print("number is 2")
break
default:
print("number is other")
break
} // number is 1
- 默认可以不写
break,并不会贯穿到后面的条件
switch number {
case 1:
print(" ")
case 2:
print("number is 2")
default:
print("number is other")
} // number is 1
2) fallthrough
- 使用
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
3) switch注意点
- switch 必须要保证能处理所有情况
-
case、default要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")
default:
print("wrong")
}
- 由于已确定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")
}
4)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", "Rose":
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
5) 区间匹配 元组匹配
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
- 可以使用
下划线或略某个值 - 关于
case匹配问题, 属于模式匹配(Pattern Matching)的范畴, 以后会再次详细展开讲解
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
6) 值绑定
- 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 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
五、where语句
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 = 0
for num in numbers where num > 0 { //使用where过滤num
sum += num
}
print(sum) //60
六、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)")
}
}