Kotlin Loops

Repeating code execution efficiently

🔄 What are Loops?

Loops allow you to repeat code multiple times without writing it over and over. They're essential for processing collections, counting, and automating repetitive tasks in your programs efficiently and elegantly. 


// Simple loop example
for (i in 1..3) {
    println("Count: $i")
}

Types of Loops

🔢

For Loop

Iterate over ranges and collections 

for (i in 1..5) {
    println(i)
}
⏳

While Loop

Repeat while condition is true 

var count = 0
while (count < 3) {
    println(count++)
}
🎯

Do-While Loop

Execute at least once, then check condition 

var x = 0
do {
    println("x = $x")
    x++
} while (x < 2)
📋

Collection Loops

Iterate through lists and arrays 

val fruits = listOf("apple", "banana")
for (fruit in fruits) {
    println(fruit)
}

🔹 For Loop Basics

The most common loop for iterating over ranges: 

fun main() {
    // Count from 1 to 5
    println("Counting up:")
    for (i in 1..5) {
        println("Number: $i")
    }
    
    // Count backwards
    println("\nCountdown:")
    for (i in 5 downTo 1) {
        println("$i...")
    }
    println("Blast off! 🚀")
}

Output:

Counting up:

Number: 1

Number: 2

Number: 3

Number: 4

Number: 5


Countdown:

5...

4...

3...

2...

1...

Blast off! 🚀

🔹 While Loop

Repeat code while a condition remains true: 

fun main() {
    var password = ""
    var attempts = 0
    
    while (password != "secret" && attempts < 3) {
        attempts++
        println("Attempt $attempts: Enter password")
        
        // Simulating user input
        password = when (attempts) {
            1 -> "wrong"
            2 -> "incorrect"
            3 -> "secret"
            else -> ""
        }
        
        if (password == "secret") {
            println("Access granted! ✅")
        } else {
            println("Wrong password! ❌")
        }
    }
}

Output:

Attempt 1: Enter password

Wrong password! ❌

Attempt 2: Enter password

Wrong password! ❌

Attempt 3: Enter password

Access granted! ✅

🔹 Do-While Loop

Execute code at least once, then check condition: 

fun main() {
    var userChoice: String
    
    do {
        println("=== Menu ===")
        println("1. Play Game")
        println("2. View Scores")
        println("3. Exit")
        println("Choose an option:")
        
        // Simulating user input
        userChoice = "2" // User chooses option 2
        
        when (userChoice) {
            "1" -> println("Starting game... 🎮")
            "2" -> println("High Score: 1000 points 🏆")
            "3" -> println("Thanks for playing! 👋")
            else -> println("Invalid choice!")
        }
        
        // For demo, we'll exit after one iteration
        userChoice = "3"
        
    } while (userChoice != "3")
}

Output:

=== Menu ===

1. Play Game

2. View Scores

3. Exit

Choose an option:

High Score: 1000 points 🏆

Thanks for playing! 👋

🔹 Looping Through Collections

Iterate over lists, arrays, and other collections: 

fun main() {
    val fruits = listOf("Apple", "Banana", "Orange", "Grape")
    val numbers = arrayOf(10, 20, 30, 40, 50)
    
    // Loop through list
    println("Fruits in basket:")
    for (fruit in fruits) {
        println("🍎 $fruit")
    }
    
    // Loop with index
    println("\nNumbers with positions:")
    for ((index, number) in numbers.withIndex()) {
        println("Position $index: $number")
    }
    
    // Loop through indices
    println("\nUsing indices:")
    for (i in fruits.indices) {
        println("${i + 1}. ${fruits[i]}")
    }
}

Output:

Fruits in basket:

🍎 Apple

🍎 Banana

🍎 Orange

🍎 Grape


Numbers with positions:

Position 0: 10

Position 1: 20

Position 2: 30

Position 3: 40

Position 4: 50


Using indices:

1. Apple

2. Banana

3. Orange

4. Grape

🧠 Test Your Knowledge

Which loop executes at least once, even if the condition is false?