1fun main() {
2    println("Hello, World!")
3}

 1fun sum(x: Int, y: Int): Int {
 2    return x + y
 3}
 4
 5// Single-Expression
 6fun mul(x: Int, y: Int) = x * y
 7
 8// Default Arguments
 9fun printMSG (msg1: String = "Hello", msg2: String) {
10    println("$msg1, $msg2!")
11}
12
13fun main() {
14    println(sum(1, 2))
15    println(mul(2, 5))
16    printMSG("Hi", "Jack")
17    printMSG(msg2 = "Kelly")
18}

1fun sum(vararg a: Int): Int {
2    var ret = 0
3    for (x in a) ret = ret + x
4    return ret
5}
6
7fun main() {
8    println(sum(1, 0, -1, 2))
9}

1fun main() {
2    val v = 1 // immutalbe
3    var x: Int // mutable
4    x = 1
5    println(x + v)
6}

 1fun main() {
 2    var notNull: String = "Hi!"
 3    // notNull = null // error
 4    var canNull: String? = "Hello!"
 5    canNull = null
 6
 7    fun len(s: String) = println(s.length)
 8    
 9    len(notNull)
10    // len(canNull) // error
11    canNull = "OAO"
12    len(canNull)
13
14    fun nullLen(s: String?) {
15        var L:Int = 0
16        if (s != null) L = s.length
17        println(L)
18    }
19    
20    canNull = null
21    nullLen(canNull)
22}

 1fun cases(obj: Any) {
 2    when (obj) {
 3        1 -> println("One")
 4        is String -> println("String")
 5        else -> println("Else")
 6    }
 7}
 8
 9fun main() {
10    cases(1)
11    cases(1.0)
12    cases("a")
13}

1fun main() {
2    val L = listOf("apple", "banana", "orange")
3    for (x in L) {
4        println("I like $x.")
5    }
6}

 1fun main() {
 2    for (i in 0..3) print(i) //0123
 3    println("")
 4    for (i in 0..8 step 2) print(i) //02468
 5    println("")
 6    for (i in 3 downTo 0) print(i) //3210
 7    println("")
 8    for (i in 8 downTo 0 step 2) print(i) //86420
 9    println("")
10}

1fun main() {
2    var i = 0
3    var sum = 0
4    while (i < 5) {
5        sum += i
6        i++
7    }
8    println(sum)
9}

1fun main() {
2    val x = 't'
3    if (x in 'a'..'e')
4        println("Good")
5    else
6        println("Bad")
7}

 1fun main() {
 2    val L: List<Int> = listOf(1, 2, 3)
 3    var mL: MutableList<Int> = mutableListOf(0)
 4    L.forEach {
 5        x -> mL.add(x)
 6    }
 7    mL.forEach {
 8        i -> println("elemetn: $i")
 9    }
10    println("L[2] = ${L.getOrNull(2)}") // 3
11    println("L[3] = ${L.getOrNull(3)}") // null
12    println("L[10] = ${L.getOrElse(10, {it})}") // 10
13    println("${L.subList(1, 2)}") // [2]
14}

 1fun main() {
 2    var mL: MutableList<Int> = mutableListOf(2, 1, 7, 5, 9, 1)
 3    println(mL.indexOf(1)) // 1
 4    println(mL.lastIndexOf(1)) // 5
 5    mL.sort() // [1, 1, 2, 5, 7, 9]
 6    println(mL.indexOf(1)) // 0
 7    println(mL.lastIndexOf(1)) // 1
 8    println(mL.indexOfFirst{ it > 5 }) // 4
 9    println(mL.binarySearch(3)) // -4
10    println(mL.binarySearch(1, 1, 5)) // 1
11    mL.fill(0)
12    println(mL) // [0, 0, 0, 0, 0, 0]
13}

 1fun main() {
 2    val S1: Set<Int> = setOf(4, 3, 2, 1)
 3    val S2: Set<Int> = setOf(1, 2, 3, 4)
 4    println("Two sets are equal: ${S1 == S2}") // true
 5    val S3: Set<Int> = setOf(0, 2, 4, 6)
 6    println("S2 union S3: ${S2 union S3}") // [1, 2, 3, 4, 0, 6]
 7    println("S2 intersect S3: ${S2 intersect S3}") // [2, 4]
 8    println("S2 subtract S3: ${S2 subtract S3}") // [1, 3]
 9    println("S3 subtract S2: ${S3 subtract S2}") // [0, 6]
10    println("S1 subtract S2: ${S1 subtract S2}") // []
11    var S4: MutableSet<Int> = mutableSetOf(1, 2, 3, 4)
12    println("${S4.add(0)}") // true
13    println("${S4.add(1)}") // false
14}

1fun main() {
2    val map = mapOf("key" to 42);
3    println("${map["key"]}") // 42
4    println("${map["key2"]}") // null
5    println("${map.getValue("key")}") // 42
6}