一、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 >= 22 {
print("我是成年人")
} else if age >= 18 {
print("我是青年者")
} else if age >= 7 {
print("我还是小孩子")
} else {
print("我是个儿童")
}
二、while
// 打印5次
var num = 5
while num > 0 {
print("num is \(num)")
num -= 1 // 不能用num--,只能用num-=1,Swift3.0后去掉了++、--的运算符
}
// 打印1次 等价于C语言中的do-while
var num = -1
repeat {
print("num is \(num)")
} while num > 0
三、for
- 闭区间运算符:a...b(意思是:a <= 取值 <= b)
- 半开区间运算符:a..<b(意思是:a<= 取值<b)
- 单侧区间:让一个区间尽可能无限远(针对数组,就是数组最大值,很好用哦,不存在数组越界)
- 区间类型:
let range1: ClosedRange<Int> = 1...3 // 闭区间
let range2: Range<Int> = 1..<3 // 半开区间
let range3: PartialRangeThrough<Int> = ...5 // 单侧
- 字符、字符串也能使用区间运算符,但默认不能再for-in中
- 带间隔的区间值
- 默认i为let,可以用var声明为变量
- 如果用不到i这个值可以用下划线进行忽略
---------------------------------------------------------------
// 闭区间运算符1
let names = ["Anna", "Alex", "Brian", "Jack"]
for i in 0...3 {
print(names[i])
} // Anna Alex Brian Jack
---------------------------------------------------------------
// 闭区间运算符2
let range = 1...3
for i in range {
print(names[i])
} // Anna Alex Brian Jack
---------------------------------------------------------------
// 闭区间运算符3
let a = 1
var b = 2
for i in a...b {
print(names[i])
} // Anna Alex
---------------------------------------------------------------
// 闭区间运算符4
for i in a...3 {
print(names[i])
} // Alex Brian Jack
---------------------------------------------------------------
// 闭区间运算符5
for var i in 0...3 { // 默认i为let,可以用var声明为变量
i += 5
print(i)
} // 6 7 8
---------------------------------------------------------------
// 闭区间运算符6
for _ in 1...3 { // 如果用不到i这个值可以用下划线进行忽略
print("for")
} // 打印了3次
---------------------------------------------------------------
// 闭区间运算符7
for name in names[0...3] {
print(name)
} // Anna Alex Brian Jack
---------------------------------------------------------------
// 半开区间运算符
for i in 1..<5 {
print(i)
} // 1 2 3 4
---------------------------------------------------------------
// 单侧区间1
for name in names[2...] { // 这个就是一直遍历到数组最大值
print(name)
}
---------------------------------------------------------------
// 单侧区间2
for name in names[...2] { // 这个就是从最小值到2
print(name)
}
---------------------------------------------------------------
// 单侧区间3
for name in names[..<2] { // 这个就是从最小值到1
print(name)
}
---------------------------------------------------------------
// 区间类型
let range = ...5 // 放到外面就没有限制了
range.contains(7) // false
range.contains(3) // true
range.contains(-3) // true
---------------------------------------------------------------
// 字符、字符串也能使用区间运算符,但默认不能再for-in中
let stringRange1 = "cc"..."ff" // 类型:CloseRange<String>
stringRange1.contains("cb") // false
stringRange1.contains("dz") // true
stringRange1.contains("fg") // false
let stringRange2 = "a"..."f"
stringRange2.contains("d") // true
stringRange2.contains("h") // false
---------------------------------------------------------------
// 字符、字符串也能使用区间运算符,但默认不能再for-in中
// \0到~囊括了所有可能要用到的ASCII字符
let charaterRange: ClosedRange<Character> = "\0"..."~"
charaterRange.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 (form: 4, through: hours, by: hourInterval) {
print(tickMark)
} // 4 6 8 10
四、switch
- case、default后面不能写打括号
- 默认可以不写break,并不会贯穿到后面的条件
- 使用fallthrough可以实现贯穿效果
- switch必须保证能处理所有情况
- case、default后面至少要有一条语句
- 如果你不想做任何事,加个break即可
- 如果能保证已处理所有情况,也可以不必使用default
- switch也支持Character、String类型
- 可以使用下划线_忽略某个值
- 关于case匹配,属于模式匹配
---------------------------------------------------------------
var number = 1
switch number {
case 1:
print("number is 1")
break
case 2:
print("number is 2")
fallthrough
default:
print("number is other")
} // number is 1
---------------------------------------------------------------
enum Answer {case right, wrong}
let answer = Answer.right
switch answer {
case Answer.right:
print("right")
case Answer.wrong:
print("wrong")
}
---------------------------------------------------------------
let string = "Jack"
switch string {
case "Jack":
fallthrough
case "Rose":
print("Right person")
default:
break
}
let string = "Jack"
switch string {
case "Jack", "Rose":
print("Right person")
default:
break
}
---------------------------------------------------------------
// 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")
}
---------------------------------------------------------------
// 值绑定 (必要时可以改成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, let y):
print("somewhere else at (\(x), \(y))")
} // on the x-axis with an x value of 2
五、where
// 用在switch中:先把值赋值给let (x, y),然后判断是否相等
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
---------------------------------------------------------------
// 用在for循环中: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来过滤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 // 加入标签可以控制外层的for循环
}
if i == 3 {
break outer // 加入标签可以控制外层的for循环
}
print("i == \(i), k == \(k)")
}
}