Swift语法基础：17 - Swift的For循环, While, Do-While, If, Switch
在Swift中, 也有控制流, 分别是For, For-In, For条件递增, While, Do-While等等, 让我们一起来探讨一下:
1.For循环
在Swift中提供两种循环, 一种是For-In, 另一种是For条件递增, 先来看第一种:
for index in 1...5 {
println("\(index) times 5 is \(index * 5)")
}
// 打印出来的结果:
//1 times 5 is 5
//2 times 5 is 10
//3 times 5 is 15
//4 times 5 is 20
//5 times 5 is 25如果你不需要知道范围内每一项的值,你可以使用下划线(_)替代变量名来忽略对值的访问:
let base = 3
let power = 10
var answer = 1
for _ in 1...power {
answer *= base
}
println("\(base) to the power of \(power) is \(answer)")
// 打印出来的结果:3 to the power of 10 is 59049在前面数组和字典的遍历就已经举过例子了, 所以这里就不再列举了.
2.For条件递增
在Swift中, 我们也可以使用使用条件递增, 只不过和OC有一些区别, 现在让我们来看看:
for var index = 0; index < 3; ++index {
println("indx is \(index)")
}
// 打印出来的结果: indx is 0
// indx is 1
// indx is 2其他的基本上都差不多, 知识在Swift中的声明不太一样.
3.While循环
While循环其实和OC也是差不多的, 让我们来看看例子:
var square = 0
var diceRoll = 0
let finalSquare = 25
var board = [Int](count: finalSquare + 1, repeatedValue: 0)
while square < finalSquare {
if ++diceRoll == 7{
diceRoll = 1
}
square += diceRoll
if square < board.count {
square += board[square]
}
}
println("\(square), \(diceRoll), \(finalSquare)")
// 打印出来的结果: 27, 3, 25原理基本上都差不多只是有一些细节需要注意一下.
4.Do-While循环
在Swift中的Do-While循环里, 和OC中的Do-While差别也不大, 让我们来看看例子:
var a = 20
var b = 10
do {
if ++b == a{
a = 0
}
} while a > b
println("\(a), \(b)")
// 打印出来的结果: 0, 205.条件语句
在Swift中, 也有判断的条件语句, 那就是if, 用法和OC一样, 没区别, 让我们来看看吧:
var temperatureInFahrenheit = 30
if temperatureInFahrenheit <= 32 {
println("It's very cold. Consider wearing a scarf.")
}
// 打印出来的结果: It's very cold. Consider wearing a scarf.和OC一样, 用 if 语句来判断条件, 如果条件成立, 那么就会返回true, 否则就是false.
6.Switch开关
在Swift中的Switch开关非常的好用, 和OC不一样, 在OC中, 如果Switch忘记写break就会报错, 但是在Swift中就不需要写这个东西, 比如:
let someCharacter: Character = "e"
switch someCharacter {
case "a", "e", "i", "o", "u":
println("\(someCharacter) is a vowel")
case "b", "c", "d", "f", "g", "h", "j", "k", "l", "m","n", "p", "q", "r", "s", "t", "v", "w", "x", "y", "z":
println("\(someCharacter) is a consonant")
default:
println("\(someCharacter) is not a vowel or a consonant")
}
// 打印出来的结果: e is a vowel在Switch中还可以这么使用:
let anotherCharacter: Character = "a"
switch anotherCharacter {
case "a":
break
case "A":
println("The letter A")
default:
println("Not the letter A")
}
// 打印出来的结果: 空的PS: 在Swift中不存在隐式贯穿, 在Swift中, 一旦case执行完毕后, 就不会继续往下执行, 所以也就不需要break了, 但如果你的case是空的, 那么就必须得写break了, 因为在Swift中, Switch的开关必须得有一个内容.
同样的, 一个case也可以包含多个模式, 比如:
7.范围匹配
let count = 3_000_000_000_000
let countedThings = "stars in the Milky Way"
var naturalCount: String
switch count {
case 0:
naturalCount = "no"
case 1...3:
naturalCount = "a few"
case 4...9:
naturalCount = "several"
case 10...99:
naturalCount = "tens of"
case 100...999:
naturalCount = "hundreds of"
case 1000...999_999:
naturalCount = "thousands of"
default:
naturalCount = "millions and millions of"
}
println("There are \(naturalCount) \(countedThings).")
// 打印出来的结果:There are millions and millions of stars in the Milky Way.好了, 这次我们就讲到这里, 下次我们继续~
