控件流 1

var optionalString: String? = "Hello"

print(optionalString == nil)

var optionalName: String? = "John Appleseed"

var greeting = "Hello!"

if let name = optionalName {

greeting = "Hello, \(name)"

}

else {

print(greeting)

}

//let nickName: String? = "ABC"

let nickName: String? = nil

let fullName: String = "John Appleseed"

let informalGreeting = "Hi \(nickName ?? fullName)"

let vegetable = "red pepper"

switch vegetable {

case "celery":

print("Add some raisins and make ants on a log.")

case "cucumber", "watercress":

print("That would make a good tea sandwich.")

case let x where x.hasSuffix("pepper"):

print("Is it a spicy \(x)?")

default:

print("Everything tastes good in soup.")

}

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

}

} }

print(largest)

var n = 2

while n < 100 {

n = n * 2

}

print(n)

var m = 2

repeat {

m = m * 2

} while m < 100

print(m)

var firstForLoop = 0

for i in 0..<4 {

firstForLoop += i

}

print(firstForLoop)

var secondForLoop = 0

for var ij in 0...4  {

secondForLoop += ij

}

print(secondForLoop)