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🔁 Kotlin Control Flow Statements – Conditions, Loops, Ranges & More

🧲 Introduction – Direct Program Logic with If, When, Loops & Breaks

Control flow statements determine how your Kotlin program makes decisions and repeats actions. These include conditional expressions (if, when), loops (for, while, do-while), and branching statements like break and continue.

Kotlin improves control structures with expression-based syntax, eliminating boilerplate and offering greater flexibility with concise logic.

🎯 In this guide, you’ll learn:

• How to use if...else and when expressions for decision making
• How to iterate using for and while loops
• How to control flow inside loops using break and continue
• How to leverage Kotlin’s ranges for loop iterations and validations

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📘 Topics Covered

🔍 Topic	📖 Description
🧭 Kotlin – Control Flow Overview	Summary of Kotlin’s conditional and loop constructs.
🔀 Kotlin – If…Else Expressions	Conditional branching using if, else, and nested expressions.
🧩 Kotlin – When Expression	Kotlin’s flexible replacement for switch-case logic.
🔁 Kotlin – For Loop	Iterating over arrays, ranges, and collections using for.
🔄 Kotlin – While Loop	Repeating tasks using while and do...while loops.
🧷 Kotlin – Break & Continue	Skipping or exiting loops with break, continue, and labeled flow.
📏 Kotlin – Ranges	Creating iterable numeric ranges using .., until, and step.

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🔍 Detailed Sections & Examples

🔀 Kotlin – If…Else Expressions

val score = 85
val grade = if (score >= 90) "A"
            else if (score >= 75) "B"
            else "C"

println(grade)  // Output: B

🧠 Explanation:

• if is an expression that returns a value.
• Supports multi-line, nested, and inline expressions.

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🧩 Kotlin – When Expression (Switch Alternative)

val day = 3
val result = when(day) {
    1 -> "Monday"
    2 -> "Tuesday"
    3 -> "Wednesday"
    else -> "Unknown"
}
println(result)  // Output: Wednesday

💡 when can replace complex if-else chains with clean branching.

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🔁 Kotlin – For Loop

val items = listOf("Kotlin", "Java", "Swift")
for (item in items) {
    println(item)
}

📌 Iterate through any iterable (lists, arrays, ranges) using for (element in collection).

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🔄 Kotlin – While Loop

var i = 0
while (i < 3) {
    println("i = $i")
    i++
}

🌀 Use while when the loop count isn’t known beforehand.

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🔁 Kotlin – Do…While Loop

var num = 0
do {
    println("Running at least once: $num")
    num++
} while (num < 1)

⏩ do...while ensures the block runs at least once.

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🧷 Kotlin – Break & Continue

for (i in 1..5) {
    if (i == 3) continue
    if (i == 5) break
    println(i)
}

📌 Output:
1
2
4

• continue skips current iteration.
• break exits the loop.

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📏 Kotlin – Ranges

for (i in 1..3) {
    println(i)
}

🧠 Kotlin offers:

• 1..5 ➝ inclusive range
• 1 until 5 ➝ excludes 5
• 5 downTo 1 ➝ reverse range
• 1..10 step 2 ➝ custom steps

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📌 Summary – Recap & Next Steps

Kotlin’s control flow is concise and powerful, giving developers a functional approach to conditional logic and iteration. Its expression-based if and when, combined with intuitive loops and range syntax, streamline everyday logic.

🔍 Key Takeaways:

• Use if...else and when as expressions that return values.
• Iterate collections or ranges with for, while, and do...while.
• Control loops with break, continue, and custom ranges.

⚙️ Practical Use Cases:

• Menu handling using when
• Iterating API data with loops
• Conditional formatting and filters in logic-heavy code

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❓ Frequently Asked Questions

❓ Can if be used as an expression in Kotlin?
✅ Yes. if returns a value and can be assigned to a variable:

val result = if (score > 50) "Pass" else "Fail"

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❓ What makes when more powerful than switch in Java?
✅ Kotlin’s when supports ranges, type checks, expressions, and has no fallthrough:

when (x) {
    in 1..10 -> println("In range")
    else -> println("Out of range")
}

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❓ How do I break out of nested loops in Kotlin?
✅ Use labeled breaks:

outer@ for (i in 1..3) {
    for (j in 1..3) {
        if (i == 2) break@outer
        println("$i, $j")
    }
}

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❓ What is the difference between 1..5 and 1 until 5?
✅ 1..5 includes 5, 1 until 5 excludes 5.

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❓ Can I use step with downTo?
✅ Yes. Example:

for (i in 10 downTo 1 step 2) {
    println(i)
}

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