For循环
For-In
我们可以使用for-in循环来遍历一个集合里的所有元素,例如由数字表示的区间、数组中的元素、字符串中的字符。
for index in 1...3{
print(index)
}
index是一个每次循环遍历开始时被自动赋值的常量,这种情况下,index在使用前不需要声明,只需要将它包含在循环的声明中,
就可以对其进行隐式声明。
let base = 3
let power = 3
var answer = 1
for _ in 1...power{
answer = base * answer
print(answer)
}
如果我们不需要知道区间内每一项的值,可以使用下划线(_)替代变量名来忽略对值的访问。
For条件递增
for(var i=0;i<3;i++){
print(i)
}
for var i=0;i<3;++i {
print(i)
}
Switch
Swift里面的switch与OC中的语句不同。在Swift中,当匹配的case分支中的代码执行完毕后,程序会终止switch语句,
而不会继续执行下一个case分支。也就是说,不需要在case分支中显示得使用break语句。
既然Swift里面的switch语句有这样的特性,那么如果想要达到贯穿执行怎么办呢?使用***fallthrough***关键字;
let someCharacter: Character = "e"
switch someCharacter {
case "a", "e", "i", "o", "u":
print("\(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":
print("\(someCharacter) is a consonant")
default:
print("\(someCharacter) is not a vowel or a consonant")
}
let anotherCharacter: Character = "a"
switch anotherCharacter {
case "a":
case "A":
print("The letter A")
default:
print("Not the letter A")
}
let anotherCharacter: Character = "a"
switch anotherCharacter {
case "a":
fallthrough
case "A":
print("The letter A")
default:
print("Not the letter A")
}
Switch的区间匹配
let count = 30
let countedThings = "stars in the Milky Way"
var naturalCount: String
switch count {
case 0:
naturalCount = "no"
case 1...9:
naturalCount = "a few"
case 10...99:
naturalCount = "tens of"
case 100...999:
naturalCount = "hundreds of"
default:
naturalCount = "thousands and millions of"
}
print("There are \(naturalCount) \(countedThings).")
Switch与元组
元组中下划线(_)可以用来匹配所有可能的值
let somePoint = (1, 1)
switch somePoint {
case (0, 0):
print("(0, 0) is at the origin")
case (_, 0):
print("(\(somePoint.0), 0) is on the x-axis")
case (0, _):
print("(0, \(somePoint.1)) is on the y-axis")
case (-2...2, -2...2):
print("(\(somePoint.0), \(somePoint.1)) is inside the box")
default:
print("(\(somePoint.0), \(somePoint.1)) is outside of the box")
}
在上面的例子中,switch语句会判断某个点是否是原点(0,0),是否在想轴上,是否在Y轴上,是否在一个以原点为中心的4*4
的矩形里,或者在这个矩形外面。
不像OC语言,Swift允许多个case匹配同一个值。也就是说,点(0,0)其实可以匹配前四个case,但是首先匹配case(0,0),
因此剩下的能够匹配的case分支都会被忽略掉。
Switch的值绑定
case分支的模式允许将匹配的值绑定到一个临时的变量或常量,这些常量或变量在该case分支里就可以被引用了
——这种行为被称为值绑定。
let anotherPoint = (2, 0)
switch anotherPoint {
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))")
}
//输出:on the x-axis with an x value of 2