苹果公司推出的新编程语言Swift简介和入门教程

var optionalString: String? = "Hello"
optionalString == nil
var optionalName: String? = "John Appleseed"
var gretting = "Hello!"
if let name = optionalName {
    gretting = "Hello, (name)"
}

 

2.3灵活的switch

Swift中的switch支持各种各样的比较操作：

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let vegetable = "red pepper"
switch vegetable {
case "celery":
    let vegetableComment = "Add some raisins and make ants on a log."
case "cucumber", "watercress":
    let vegetableComment = "That would make a good tea sandwich."
case let x where x.hasSuffix("pepper"):
    let vegetableComment = "Is it a spicy (x)?"
default:
    let vegetableComment = "Everything tastes good in soup."
}

 

2.4其它循环

for-in除了遍历数组也可以用来遍历字典：

 

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let interestingNumbers = [
    "Prime": [2, 3, 5, 7, 11, 13],
    "Fibonacci": [1, 1, 2, 3, 5, 8],
    "Square": [1, 4, 9, 16, 25],
]
var largest = 0
for (kind, numbers) in interestingNumbers {
    for number in numbers {
        if number > largest {
            largest = number
        }
    }
}
largest

 

while循环和do-while循环：
 

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var n = 2
while n < 100 {
    n = n * 2
}

var m = 2
do {
    m = m * 2
} while m < 100
m

 

Swift支持传统的for循环，此外也可以通过结合..（生成一个区间）和for-in实现同样的逻辑。

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var firstForLoop = 0
for i in 0..3 {
    firstForLoop += i
}
firstForLoop
var secondForLoop = 0
for var i = 0; i < 3; ++i {
    secondForLoop += 1
}
secondForLoop