Swift开发基础02-流程控制
if-slse
1 2 3 4 5 6 7 8 9 10 | 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
while
1 2 3 4 5 | var num = 5 while num > 0 { print( "num is \(num)" ) num -= 1 } // 打印了5次 |
1 2 3 4 | var num = -1 repeat { print( "num is \(num)" ) } while num > 0 // 打印了1次 |
repeat-while相当于C语言中的do-while
这里不用num--,是因为从Swift3开始,去除了自增(++)、自减(--)运算符
for
1、基本使用
闭区间运算符:a...b, a <= 取值 <= b
1 2 3 4 | let names = [ "Anna" , "Alex" , "Brian" , "Jack" ] for i in 0...3 { print(names[i]) } // Anna Alex Brian Jack |
1 2 3 4 5 | // i默认是let,有需要时可以声明为var for var i in 1...3 { i += 5 print(i) } // 6 7 8 |
1 2 3 | <br> for _ in 1...3 { print( "for" ) } // 打印了3次 |
1 2 3 4 | <br>let range = 1...3 for i in range { print(names[i]) } // Alex Brian Jack |
1 2 3 4 5 6 7 8 | <br>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 |
半开区间运算符:a..<b, a <= 取值 < b
1 2 3 | for i in 1..<5 { print(i) } // 1 2 3 4 |
2、for-区间运算符用在数组上
1 2 3 4 | let names = [ "Anna" , "Alex" , "Brian" , "Jack" ] for name in names[0...3] { print(name) } // Anna Alex Brian Jack |
单侧区间:让区间朝一个方向尽可能的远
1 2 3 4 5 6 7 8 9 | 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 |
1 2 3 4 | let range = ...5 range.contains(7) // false range.contains(4) // true range.contains(-3) // true |
3、区间类型
1 2 3 | 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
1 2 3 4 5 6 7 8 | let stringRange1 = "cc" ... "ff" // ClosedRange<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 |
// \0到~囊括了所有可能要用到的ASCII字符
1 2 3 | let characterRange: ClosedRange<Character> = "\0" ... "~" characterRange.contains( "G" ) // true |
4、带间隔的区间值
1 2 3 4 5 6 7 | 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
case、default后面不能写大括号{}
1 2 3 4 5 6 7 8 9 10 11 12 | 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 |
默认可以不写break,并不会贯穿到后面的条件
1 2 3 4 5 6 7 8 9 | 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 |
使用fallthrough可以实现贯穿效果
1 2 3 4 5 6 7 8 9 10 11 12 | 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 |
注意点:
switch必须要保证能处理所有情况
case、default后面至少要有一条语句 n 如果不想做任何事,加个break即可
1 2 3 4 5 6 7 8 9 10 | var number = 1 switch number { case 1: print( "number is 1" ) 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
1 2 3 4 5 6 7 8 | enum Answer { case right, wrong } let answer = Answer.right switch answer { case Answer.right: print( "right" ) case Answer.wrong: print( "wrong" ) } |
1 2 3 4 5 6 7 | // 由于已确定answer是Ansewer类型,因此可以省略Answer switch answer { case .right: print( "right" ) case .wrong: print( "wrong" ) } |
复合条件
switch也支持Character、String类型
1 2 3 4 5 6 7 8 9 10 | let string = "Jack" switch string { case "Jack" : fallthrough case "Rose" : print( "Right person" ) default : break } // Right person |
1 2 3 4 5 6 7 | let character: Character = "a" switch character { case "a" , "A" : print( "The letter A" ) default : print( "Not the letter A" ) } // The letter A |
1 2 3 4 5 6 7 | switch string { case "Jack" , "Rose" : print( "Right person" ) default : break } // Right person |
区间匹配、元组匹配
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | 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 _ 忽略某个值
关于case匹配问题,属于模式匹配(Pattern Matching)的范畴
1 2 3 4 5 6 7 8 9 10 11 12 13 | 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(必要时let也可以改为var)
1 2 3 4 5 6 7 8 9 | 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 |
where
1 2 3 4 5 6 7 8 9 | 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 |
1 2 3 4 5 6 7 | // 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 |
标签语句
1 2 3 4 5 6 7 8 9 10 11 12 | 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)" ) } } |
将来的你会感谢今天如此努力的你!
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