fun main() {
  // Code goes here
}

main() 函數(shu)是每個 Kotlin 程序的起點，在(zai)(zai)執行(xing)之前必須包(bao)含在(zai)(zai)代碼中

println("Greetings, earthling!")
print("Take me to ")
print("your leader.")

/* 
打(da)印:
Greetings, earthling!
Take me to your leader.
*/

// 這是單行注釋

/*
這個(ge)
注釋
用(yong)于
多
行
*/

fun main() {
  println("I will be printed first.")
  println("I will be printed second.")
  println("I will be printed third.")
}

var age = 25
age = 26  

val goldenRatio = 1.618

// 以下變(bian)量(liang)在雙(shuang)引號內(nei)分配了一個文本值
// 因(yin)此推斷的類(lei)型(xing)是 String

var color = "Purple" 

var streetAddress = "123 Main St."
var cityState = "Brooklyn, NY" 

println(streetAddress + " " + cityState) 
// 打印: 123 Main St. Brooklyn, NY 

var address = "123 Main St."
println("The address is $address") 
// 打印: The address is 123 Main St.

var monument = "the Statue of Liberty"

println(monument.capitalize())
// 打(da)印: The Statue of Liberty
println(monument.length)
// 打印: 21

5 + 7  // 12
9 - 2  // 7
8 * 4  // 32
25 / 5 // 5 
31 % 2 // 1 

+ 加法、- 減法、* 乘法、/ 除法和 % 模數

5 + 8 * 2 / 4 - 3 // 6 
3 + (4 + 4) / 2   // 7
4 * 2 + 1 * 7     // 15
3 + 18 / 2 * 1    // 12  
6 - 3 % 2 + 2     // 7   

var batteryPercentage = 80

// 長(chang)語法
batteryPercentage = batteryPercantage + 10 

// 帶(dai)有增廣賦值運算符(fu)的短(duan)句(ju)法(fa)
batteryPercentage += 10 

var year = 2019 
year++ // 2020
year-- // 2019 

Math.pow(2.0, 3.0)  // 8.0
Math.min(6, 9)      // 6 
Math.max(10, 12)    // 12
Math.round(13.7)    // 14

var morning = true

if (morning) {
  println("Rise and shine!")
}
// 打印(yin): Rise and shine!

var rained = false

if (rained) {
  println("今天不需要給(gei)植物澆水。")
} else {
  println("植物需(xu)要澆水！")
}
// 打印: 植物需要澆水！

var age = 65

if (age < 18 ) {
  println("您(nin)被(bei)視為未成(cheng)年(nian)人")
} else if (age < 60) {
  println("您被(bei)視為(wei)成(cheng)年人")
} else {
  println("你被認(ren)為是高級")
}

// 打印: 你被(bei)認為是高級

var myAge = 19
var sisterAge = 11
var cousinAge = 11

myAge > sisterAge  // true
myAge < cousinAge  // false
myAge >= cousinAge // true
myAge <= sisterAge // false

var humid = true
var raining = true
var jacket = false

println(!humid)
// 打印: false
println(jacket && raining)
// 打(da)印(yin): true
println(humid || raining)
// 打印(yin): true

var humid = true
var raining = true
var shorts = false
var sunny = false

// true AND true
println(humid && raining) //  true
// true AND false
println(humid && shorts)  //  false
// false AND true
println(sunny && raining) //  false
// false AND false
println(shorts && sunny)  // false

var late = true
var skipBreakfast = true
var underslept = false
var checkEmails = false

// true OR true
println(skipBreakfast || late) //  true
// true OR false
println(late || checkEmails) //  true
// false OR true
println(underslept || late) //  true
// false OR false
println(checkEmails || underslept) // false

var hungry = true
var full = false

println(!hungry) //  false
println(!full) //  true

!true && (false || true) // false
/*
(false || true) 被(bei)評估首先返回 true。
然后，評估 !true && true 并返回最終(zhong)結果 false
*/

!false && true || false // true
/*
!false 被評估首先返回(hui) true。 
然后評估(gu) true && true，返回 true。
那么(me)，真|| 評估 false 最終返回 true
*/

var studied = true
var wellRested = true

if (wellRested) {
  println("祝你今天好運！")
  if (studied) {
    println("你應該為考試(shi)做好準備！")
  } else {
    println("考試(shi)前花幾個小時學習(xi)！")
  }
}

// 打印: 祝你今天好運！
// 打印: 你應該為考試做好準備(bei)！

var grade = "A"

when(grade) {
  "A" -> println("很棒的工作！")
  "B" -> println("做得太好了！")
  "C" -> println("你(ni)通過了！")
  else -> println("關！下次一(yi)定(ding)要多準備！")
}
// 打印: 很棒的工作！

var height = 46 // inches

if (height in 1..53) {
  println("抱歉，您必須至少 54 英寸才能(neng)乘坐過山(shan)車")
}
// Prints: 抱歉，您必(bi)須(xu)至少 54 英(ying)寸才能乘坐過山車

var myAge = 22
var sisterAge = 21

myAge == sisterAge // false
myAge !== sisterAge // true

var programmingLanguages = listOf("C#", "Java", "Kotlin", "Ruby") 

var fruits = mutableListOf("Orange", "Apple", "Banana", "Mango") 

var cars = listOf("BMW", "Ferrari", "Volvo", "Tesla")

println(cars[2]) // Prints: Volvo

var worldContinents = listOf("Asia", "Africa", "North America", "South America", "Antarctica", "Europe", "Australia")

println(worldContinents.size) // Prints: 7

var primaryColors = setOf("Red", "Blue", "Yellow")

var womenInTech = mutableSetOf("Ada Lovelace",  "Grace Hopper",  "Radia Perlman",  "Sister Mary Kenneth Keller")

var averageTemp = mapOf("winter" to 35,  "spring" to 60,  "summer" to 85, "fall" to 55)

var europeanDomains = mutableMapOf("Germany" to "de", "Slovakia" to "sk", "Hungary" to "hu", "Norway" to "no")

var oscarWinners = mutableMapOf("Parasite" to "Bong Joon-ho", "Green Book" to "Jim Burke", "The Shape Of Water" to "Guillermo del Toro")

println(oscarWinners.keys)
// Prints: [Parasite, Green Book, The Shape Of Water]

println(oscarWinners.values)
// Prints: [Bong Joon-ho, Jim Burke, Guillermo del Toro]

println(oscarWinners["Parasite"])
// Prints: Bong Joon-ho

var worldCapitals = mutableMapOf("United States" to "Washington D.C.", "Germany" to "Berlin", "Mexico" to "Mexico City", "France" to "Paris")

worldCapitals.put("Brazil", "Brasilia")
println(worldCapitals)
// Prints: {United States=Washington D.C., Germany=Berlin, Mexico=Mexico City, France=Paris, Brazil=Brasilia}

worldCapitals.remove("Germany")
println(worldCapitals)
// Prints: {United States=Washington D.C., Mexico=Mexico City, France=Paris, Brazil=Brasilia}

fun greet() {
  println("Hey there!")
}

fun main() {
  // Function call
  greet() // Prints: Hey there!
}

fun birthday(name: String, age: Int) {
   println("Happy birthday $name! You turn $age today!")
}

fun main() {
  birthday("Oscar", 26) 
  // Prints: Happy birthday Oscar! You turn 25 today!
  birthday("Amarah", 30) 
  // Prints: Happy birthday Amarah! You turn 30 today!
}

fun favoriteLanguage(name, language = "Kotlin") {
  println("Hello, $name. Your favorite programming language is $language")  
}

fun main() {
  favoriteLanguage("Manon") 
  // Prints: Hello, Manon. Your favorite programming language is Kotlin
  
  favoriteLanguage("Lee", "Java") 
  // Prints: Hello, Lee. Your favorite programming language is Java
}

fun findMyAge(currentYear: Int, birthYear: Int) {
   var myAge = currentYear - birthYear
   println("I am $myAge years old.")
}

fun main() {
  findMyAge(currentYear = 2020, birthYear = 1995)
  // Prints: I am 25 years old.
  findMyAge(birthYear = 1920, currentYear = 2020)
  // Prints: I am 100 years old.
}

// Return type is declared outside the parentheses
fun getArea(length: Int, width: Int): Int {
  var area = length * width

  // return statement
  return area
}

fun main() {
  var myArea = getArea(10, 8)
  println("The area is $myArea.")
  // Prints: The area is 80.
}

fun fullName(firstName: String, lastName: String) = "$firstName $lastName"

fun main() {
  println(fullName("Ariana", "Ortega")) 
  // Prints: Ariana Ortega
  println(fullName("Kai", "Gittens")) 
  // Prints: Kai Gittens
}

fun main() {
  // Anonymous Function:
  var getProduct = fun(num1: Int, num2: Int): Int {
     return num1 * num2
  }
  println(getProduct(8, 3)) 
  // Prints: 24

  // Lambda Expression
  var getDifference = { num1: Int, num2: Int -> num1 - num2 }
  println(getDifference(10, 3))
  // Prints: 7
}

// 具有包含默認值的屬性的類
class Student {
  var name = "Lucia"
  var semester = "Fall"
  var gpa = 3.95
}

// 沒有類體的簡寫語法(fa)
class Student 

// Class
class Student {
  var name = "Lucia"
  var semester = "Fall"
  var gpa = 3.95
}

fun main() {
  var student = Student()   
  // Instance
  println(student.name)     
  // Prints: Lucia
  println(student.semester) 
  // Prints: Fall
  println(student.gpa)      
  // Prints: 3.95  
} 

class Student(val name: String, val gpa: Double, val semester: String, val estimatedGraduationYear: Int) 

fun main() {
  var student = Student("Lucia", 3.95, "Fall", 2022) 
  println(student.name)     
  // Prints: Lucia
  println(student.gpa)      
  // Prints: 3.95
  println(student.semester) 
  // Prints: Fall
  println(student.estimatedGraduationYear) 
  // Prints: 2022
}

class Student(val name: String, val gpa: Double, val semester: String, val estimatedGraduationYear: Int) {
  init {
    println("$name has ${estimatedGraduationYear - 2020} years left in college.")
  }
}

fun main() {
  var student = Student("Lucia", 3.95, "Fall", 2022)
  // Prints: Lucia has 2 years left in college. 
}