Android Academy · Lesson

Control Flow

Use if/else expressions, when statements, for and while loops to control program logic in Kotlin.

Control Flow is a free Android Academy lesson on CoddyKit — lesson 3 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Android Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Control Flow Overview

Control flow lets your program make decisions and repeat actions.

if/else — choose between paths
when — match a value against multiple cases
for — repeat over a range or collection
while — repeat while a condition is true

if/else as an Expression

In Kotlin, if/else is an expression — it returns a value, so you can assign it directly:

fun main() {
    val score = 75

    // Traditional style
    if (score >= 60) {
        println("Pass")
    } else {
        println("Fail")
    }

    // Expression style
    val grade = if (score >= 90) "A"
                else if (score >= 75) "B"
                else if (score >= 60) "C"
                else "F"
    println("Grade: $grade")
}

The when Expression

when is Kotlin's powerful replacement for switch/case:

Matches against any value, not just integers
Can be used as an expression (returns a value)
The else branch catches everything else

when in Action

Use when to handle multiple cases cleanly:

fun main() {
    val day = 3

    val name = when (day) {
        1 -> "Monday"
        2 -> "Tuesday"
        3 -> "Wednesday"
        4, 5 -> "Thu or Fri"   // multiple values
        6, 7 -> "Weekend"
        else -> "Unknown"
    }
    println(name)  // Wednesday

    // when with a range
    val temp = 28
    val feel = when {
        temp < 10 -> "Cold"
        temp < 25 -> "Comfortable"
        else -> "Hot"
    }
    println(feel)  // Hot
}

for Loops

Use for to iterate over ranges, lists, and other collections:

1..5 — range from 1 to 5 (inclusive)
1 until 5 — range from 1 to 4 (exclusive end)
10 downTo 1 — counting down
1..10 step 2 — skip every other value

for Loop Examples

Iterate over ranges and collections:

fun main() {
    // Range
    for (i in 1..5) print("$i ")  // 1 2 3 4 5
    println()

    // Until (excludes end)
    for (i in 0 until 3) print("$i ")  // 0 1 2
    println()

    // Step
    for (i in 0..10 step 3) print("$i ")  // 0 3 6 9
    println()

    // List
    val fruits = listOf("Apple", "Banana", "Cherry")
    for (fruit in fruits) println(fruit)
}

while & do-while

while repeats as long as a condition is true. do-while runs the body at least once before checking the condition.

while Loop Example

Count down using while:

fun main() {
    var count = 5
    while (count > 0) {
        println("Count: $count")
        count--
    }
    println("Done!")

    // do-while runs body first
    var x = 0
    do {
        println("x = $x")
        x++
    } while (x < 3)
}

break & continue

Control loop execution with:

break — exit the loop immediately
continue — skip this iteration and go to the next

Kotlin also supports labeled breaks for nested loops: break@outer.

Quick Check

What does 1 until 5 produce?

Recap: Control Flow

You now know how to control program flow in Kotlin:

if/else as an expression — assign results directly
when — clean replacement for switch/case
for with ranges, until, step, downTo
while and do-while

Next: Kotlin's killer feature — null safety.

Frequently asked questions

Is the “Control Flow” lesson free?

Yes — the full text of “Control Flow” is free to read here on the web, and the Android Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Android Academy course, upgrade to CoddyKit PRO.

What will I learn in “Control Flow”?

Use if/else expressions, when statements, for and while loops to control program logic in Kotlin. You practise Android Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Android Academy?

No prior experience is required. Android Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 3, so you can start here or from the beginning and move at your own pace.

How long does the “Control Flow” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Android Academy lesson?

Yes. Every Android Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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