func sayHelloAgain(personName: String) -> String {
    return "Hello again, " + personName + "!"
}
  
print(sayHelloAgain(personName: "Anna"))
// prints "Hello again, Anna!"

func sayHelloWorld() -> String {
    return "hello, world"
}
print(sayHelloWorld())
// prints "hello, world"

for index in 1...5 {
    print("\(index) times 5 is \(index * 5)")
}
// 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

let base = 3
let power = 10
var answer = 1
for _ in 1...power {
    answer *= base
}
print("\(base) to the power of \(power) is \(answer)")
// 输出 "3 to the power of 10 is 59049"

var someInts = [Int]()
print("someInts is of type [Int] with \(someInts.count) items.")
// 打印 "someInts is of type [Int] with 0 items."

var threeDoubles = [Double](count: 3, repeatedValue:0.0)
// threeDoubles 是一种 [Double] 数组，等价于 [0.0, 0.0, 0.0]

var emptyString = ""               // 空字符串字面量
var anotherEmptyString = String()  // 初始化方法
// 两个字符串均为空并等价。

if emptyString.isEmpty {
    print("Nothing to see here")
}
// 打印输出："Nothing to see here"

let b = 10
var a = 5
a = b
// a 现在等于 10

1 + 2       // 等于 3
5 - 3       // 等于 2
2 * 3       // 等于 6
10.0 / 2.5  // 等于 4.0

"hello, " + "world"  // 等于 "hello, world"

//变量声明
var x = 1

//声明多个变量
var x = 1, y = 2

//带类型声明
var msg: String
//变量赋值
msg = "Hello"

//声明常量
let pi = 3.14159