定义函数(参数name，day类型string，返回值->String)

func greet(name: String, day: String) -> String {
return "Hello \(name), today is \(day)."
}
greet("Bob", "Tuesday")

func getGasPrices() -> (Double, Double, Double) {
return (3.59, 3.69, 3.79)
}
getGasPrices()