Kotlin Fundamentals

fun main() {
    // Start the demonstration program.
    println("MonsterBattles started")
}

MonsterBattles started

fun main() {
    print("Monster: ")
    println("Pyron")
    println("Ready to battle")
}

Monster: Pyron
Ready to battle

package nl.monsterbattles.demo

import kotlin.math.max

fun main() {
    // max is imported from kotlin.math.
    println(max(1, 18))
}

18

fun main() {
    val monsterName = "Pyron"
    var currentHp = 100
    currentHp -= 20
    println("$monsterName: $currentHp HP")
}

Pyron: 80 HP

const val GAME_NAME = "MonsterBattles"

fun main() {
    println("Welcome to $GAME_NAME")
}

Welcome to MonsterBattles

fun main() {
    val hp: Int = 100
    val totalBattles: Long = 2L
    val ratio: Double = 0.5
    val bonus: Float = 1.5f
    val alive: Boolean = true
    val rank: Char = 'A'
    val name: String = "Pyron"
    println("$name | $hp | $totalBattles | $ratio | $bonus | $alive | $rank")
}

Pyron | 100 | 2 | 0.5 | 1.5 | true | A

fun main() {
    val attack = 30            // Inferred as Int.
    val defense: Int = 12     // Explicit Int.
    println(attack - defense)
}

18

fun main() {
    val attack = 30
    val defense = 12
    val rawDamage = attack - defense
    println(rawDamage > 0)
    println(7 % 3)
}

true
1

fun main() {
    val firstExists = true
    val secondExists = true
    val sameMonster = false
    val canBattle = firstExists && secondExists && !sameMonster
    println(canBattle)
}

true

fun main() {
    val selectedMonster: String? = null
    // The right-hand side is skipped when null.
    val valid = selectedMonster != null && selectedMonster.length > 2
    println(valid)
}

false

fun main() {
    val name = "Aquara"
    val hp = 110
    println("$name has ${hp - 18} HP remaining")
}

Aquara has 92 HP remaining

fun calculateDamage(attack: Int, defense: Int): Int {
    return maxOf(1, attack - defense)
}

fun main() {
    println(calculateDamage(30, 12))
}

18

fun isAlive(hp: Int): Boolean = hp > 0

fun main() {
    println(isAlive(92))
}

true

fun hit(attack: Int, defense: Int = 10) = maxOf(1, attack - defense)

fun main() {
    println(hit(attack = 30))
    println(hit(defense = 12, attack = 30))
}

20
18

fun main() {
    val pyronSpeed = 110
    val aquaraSpeed = 95
    if (pyronSpeed > aquaraSpeed) {
        println("Pyron starts")
    } else {
        println("Aquara starts")
    }
}

Pyron starts

fun main() {
    val starter = if (110 >= 95) "Pyron" else "Aquara"
    println(starter)
}

Pyron

fun main() {
    val element = "FIRE"
    val display = when (element) {
        "FIRE" -> "Fire monster"
        "WATER" -> "Water monster"
        "WIND" -> "Wind monster"
        else -> "Unknown monster"
    }
    println(display)
    println(when { 110 > 95 -> "Pyron starts"; else -> "Aquara starts" })
}

Fire monster
Pyron starts

fun main() {
    for (turn in 1..2) println("Turn $turn")
    var hp = 2
    while (hp > 0) hp--
    println("HP: $hp")
    do { println("Battle ended") } while (false)
}

Turn 1
Turn 2
HP: 0
Battle ended

fun main() {
    for (turn in 1..5) {
        if (turn == 2) continue
        if (turn == 4) break
        println("Turn $turn")
    }
}

Turn 1
Turn 3

fun main() {
    println((1..3).toList())
    println((1 until 3).toList())
    println((5 downTo 1 step 2).toList())
}

[1, 2, 3]
[1, 2]
[5, 3, 1]

fun main() {
    val monsterName: String? = "Pyron"
    if (monsterName != null) {
        println(monsterName.length)
    }
}

5

fun main() {
    val name: String? = null
    println(name?.length)
}

null

fun main() {
    val monsterName: String? = null
    println(monsterName ?: "Unknown Monster")
}

Unknown Monster

fun main() {
    val name: String? = "Pyron"
    // This succeeds, but a null value would crash.
    println(name!!.length)
}

5

fun main() {
    val value: Any = "Pyron"
    if (value is String) {
        println(value.uppercase())
    }
}

PYRON

fun main() {
    val value: Any = 100
    val name = value as? String
    println(name ?: "No monster name")
}

No monster name

fun announce(value: Any): Unit {
    println(value)
}

fun fail(message: String): Nothing = error(message)

fun main() {
    announce("Monster ready")
    // fail("Not ready") would throw and never return.
}

Monster ready

fun unfinishedBattle(): Int = TODO("Implement battle rules")

fun main() {
    // Never execute a TODO placeholder in the finished app.
    println("TODO() compiles, but throws when called")
}

TODO() compiles, but throws when called

fun calculateDamage(attack: Int, defense: Int): Int {
    require(attack >= 0) { "Attack must be non-negative" }
    require(defense >= 0) { "Defense must be non-negative" }
    return maxOf(1, attack - defense)
}

fun main() {
    println(calculateDamage(30, 12))
}

18

fun main() {
    val names: List<String> = listOf("Pyron", "Aquara")
    val selected = mutableListOf("Pyron")
    selected.add("Aquara")
    println(names.size)
    println(selected)
}

2
[Pyron, Aquara]

fun calculateDamage(attack: Int, defense: Int): Int =
    maxOf(1, attack - defense)

fun main() {
    val pyronName = "Pyron"
    val pyronAttack = 30
    val pyronDefense = 10
    val pyronSpeed = 110
    var pyronHp = 100

    val aquaraName = "Aquara"
    val aquaraAttack = 25
    val aquaraDefense = 12
    val aquaraSpeed = 95
    var aquaraHp = 110

    // At equal speed, the first selected monster begins.
    var pyronTurn = pyronSpeed >= aquaraSpeed
    var turns = 0
    var rounds = 0
    println("${if (pyronTurn) pyronName else aquaraName} starts")

    while (pyronHp > 0 && aquaraHp > 0) {
        if (turns % 2 == 0) rounds++
        turns++
        if (pyronTurn) {
            val damage = calculateDamage(pyronAttack, aquaraDefense)
            aquaraHp = maxOf(0, aquaraHp - damage)
            println("Turn $turns: $pyronName hits $aquaraName for $damage (HP: $aquaraHp)")
        } else {
            val damage = calculateDamage(aquaraAttack, pyronDefense)
            pyronHp = maxOf(0, pyronHp - damage)
            println("Turn $turns: $aquaraName hits $pyronName for $damage (HP: $pyronHp)")
        }
        pyronTurn = !pyronTurn
    }

    println("Winner: ${if (pyronHp > 0) pyronName else aquaraName}")
    println("Rounds: $rounds | Turns: $turns")
    println("Final HP: $pyronName=$pyronHp, $aquaraName=$aquaraHp")
}

Pyron starts
Turn 1: Pyron hits Aquara for 18 (HP: 92)
Turn 2: Aquara hits Pyron for 15 (HP: 85)
Turn 3: Pyron hits Aquara for 18 (HP: 74)
Turn 4: Aquara hits Pyron for 15 (HP: 70)
Turn 5: Pyron hits Aquara for 18 (HP: 56)
Turn 6: Aquara hits Pyron for 15 (HP: 55)
Turn 7: Pyron hits Aquara for 18 (HP: 38)
Turn 8: Aquara hits Pyron for 15 (HP: 40)
Turn 9: Pyron hits Aquara for 18 (HP: 20)
Turn 10: Aquara hits Pyron for 15 (HP: 25)
Turn 11: Pyron hits Aquara for 18 (HP: 2)
Turn 12: Aquara hits Pyron for 15 (HP: 10)
Turn 13: Pyron hits Aquara for 18 (HP: 0)
Winner: Pyron
Rounds: 7 | Turns: 13
Final HP: Pyron=10, Aquara=0