Exploring For Loops in Kotlin: A Beginner's Guide

Understanding Loop Structures

Hello and welcome to today's journey into loops in Kotlin! Imagine you've been assigned the task to count the trees in your area. Will you do it individually? That's not efficient, right? That's where loops come to the rescue, saving both time and effort by automating repetitive tasks. Kotlin offers two types of loops, for and while . Our focus today is on for loops, which are used when the number of repetitions is known.

Introduction to 'For' Loop in Kotlin

Let's start with the for loop. It's an orderly and efficient way of accomplishing tasks repetitively in Kotlin. If you have a list of names and want to print them, you can use the for loop: Kotlin fun main() {// Our list of names val names = listOf("John", "Sarah", "Jane", "Tom") // Our 'for' loop for (name in names) {println(name) // Prints each name in the list}} fun main() {// Our list of names val names = listOf("John", "Sarah", "Jane", "Tom") // Our 'for' loop for (name in names) {println(name) // Prints each name in the list}} Every iteration of the loop picks a new name from names and prints it.

Variations of 'For' Loop in Kotlin

Are you ready to explore for loops further? Kotlin provides the flexibility to denote ranges that define a start and end value. To print numbers from 1 to 5, you can do: Kotlin fun main() {// Loop from 1 to 5 and print each number for (i in 1..5) {println(i) // Outputs numbers 1 through 5}} fun main() {// Loop from 1 to 5 and print each number for (i in 1..5) {println(i) // Outputs numbers 1 through 5}} To execute a loop in reverse, we can use the downTo keyword: Kotlin fun main() {// Loop from 5 to 1 for (i in 5 downTo 1) {println(i) // Outputs numbers 5 to 1 in descending order}} fun main() {// Loop from 5 to 1 for (i in 5 downTo 1) {println(i) // Outputs numbers 5 to 1 in descending order}}

'For' Loop in Action

It's time to practice! If you want to print the numbers 1 through 10 and all elements of an array, refer to the example below: Kotlin fun main() {// Loop to print numbers 1 through 10 for (num in 1..10) {println(num) // Prints numbers 1 to 10} // Loop to iterate through an array val numbers = arrayOf(1, 2, 3, 4, 5) for (n in numbers) {println(n) // Prints numbers 1 to 5}} In a for loop, if you want to access the index along with the value: Kotlin fun main() {// Our list of names val names = listOf("John", "Sarah", "Jane", "Tom") // Loop through the list withIndex() for ((index, value) in names.withIndex()) {println("The element at $index is $value") // Prints index and corresponding name} // Alternatively you can use .indices property to get a valid index range for array for (i in names.indices) {println("The element at $i is ${names[i]}") // Prints index and corresponding name}}

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Kotlin

fun main() {
    // Our list of names
    val names = listOf("John", "Sarah", "Jane", "Tom")

    // Our 'for' loop
    for (name in names) {
        println(name)  // Prints each name in the list
    }
}

Kotlin

fun main() {
    // Loop from 1 to 5 and print each number
    for (i in 1..5) {
        println(i)  // Outputs numbers 1 through 5
    }
}

Kotlin

fun main() {
    // Loop from 5 to 1
    for (i in 5 downTo 1) {
        println(i) // Outputs numbers 5 to 1 in descending order
    }
}

Kotlin

fun main() {
    // Loop to print numbers 1 through 10
    for (num in 1..10) {
        println(num)  // Prints numbers 1 to 10
    }

    // Loop to iterate through an array
    val numbers = arrayOf(1, 2, 3, 4, 5)
    for (n in numbers) {
        println(n)  // Prints numbers 1 to 5
    }
}

Kotlin

fun main() {
    // Our list of names
    val names = listOf("John", "Sarah", "Jane", "Tom")
    
    // Loop through the list withIndex()
    for ((index, value) in names.withIndex()) {
        println("The element at $index is $value")  // Prints index and corresponding name
    }

    // Alternatively you can use .indices property to get a valid index range for array
    for (i in names.indices) {
        println("The element at $i is ${names[i]}")  // Prints index and corresponding name
    }
}

Kotlin

fun main() {
    // Loop over a range of numbers
    for (i in 1..3) {
        val innerValue = "hello"  // Declare a variable in the loop
    }
    println(innerValue)  // Error! innerValue is out of the scope
}

fun main() {
    // Loop over a range of numbers
    for (i in 1..3) {
        val innerValue = "hello"  // Declare a variable in the loop
    }
    println(innerValue)  // Error! innerValue is out of the scope
}

Kotlin

for (i in 1..3) println("Loop iteration: $i")  // Directly prints each iteration

var outsideVar = 0
for (i in 1..3) outsideVar = i  // Updates an externally declared variable
println("Last updated value: $outsideVar")  // Correctly prints: Last updated value: 3

Kotlin

// Attempting multiple statements without braces - This will cause an error
for (i in 1..3) println("Iteration: $i") val squared = i * i println("Squared: $squared")

Kotlin

  1..4 // 1, 2, 3, 4
  1 until 4 // 1, 2, 3
  4 downTo 1 // 4, 3, 2, 1
  0..8 step 2 // 0, 2, 4, 6, 8
  8 downTo 0 step 2 // 8, 6, 4, 2, 0

  1..4 // 1, 2, 3, 4
  1 until 4 // 1, 2, 3
  4 downTo 1 // 4, 3, 2, 1
  0..8 step 2 // 0, 2, 4, 6, 8
  8 downTo 0 step 2 // 8, 6, 4, 2, 0

Kotlin

fun main() {
    // Loop over a range of numbers
    for (i in 1..3) {
        val innerValue = "hello"  // Declare a variable in the loop
    }
    println(innerValue)  // Error! innerValue is out of the scope
}

Kotlin

for (i in 1..3) println("Loop iteration: $i")  // Directly prints each iteration

var outsideVar = 0
for (i in 1..3) outsideVar = i  // Updates an externally declared variable
println("Last updated value: $outsideVar")  // Correctly prints: Last updated value: 3

Kotlin

// Attempting multiple statements without braces - This will cause an error
for (i in 1..3) println("Iteration: $i") val squared = i * i println("Squared: $squared")

Kotlin

  1..4 // 1, 2, 3, 4
  1 until 4 // 1, 2, 3
  4 downTo 1 // 4, 3, 2, 1
  0..8 step 2 // 0, 2, 4, 6, 8
  8 downTo 0 step 2 // 8, 6, 4, 2, 0

Understanding Loop Structures

Introduction to 'For' Loop in Kotlin

Variations of 'For' Loop in Kotlin

'For' Loop in Action

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Variable Scopes

Shorthand Loop Syntax

Cheat Sheet for Kotlin Ranges

Lesson Summary and Upcoming Practice