Loops in Kotlin

# CHAPTER 8

Loops in Kotlin #

1. Chapter Introduction #

2. Learning Objectives #

• Understand and create Kotlin Ranges (.., downTo, step).

• Use the for loop to iterate over ranges and collections.

• Use while and do-while loops.

• Stop or skip loop iterations using break and continue.

• Build a Mini Project: Multiplication Table Generator.

3. Understanding Ranges #

• 1..5 : Creates a range from 1 to 5 (inclusive: 1, 2, 3, 4, 5)

• 1 until 5 : Creates a range from 1 to 4 (exclusive of the last number)

• 5 downTo 1 : Counts backward (5, 4, 3, 2, 1)

4. The for Loop #

fun main() {
    // Iterating through a standard range
    for (i in 1..5) {
        println("Iteration: $i")
    }
}

#### Advanced for Loop Features You can control the iteration step using step, or count backwards using downTo.

fun main() {
    println("Counting by 2s:")
    for (i in 1..10 step 2) {
        print("$i ") // 1 3 5 7 9
    }

    println("\nCounting backwards:")
    for (i in 5 downTo 1) {
        print("$i ") // 5 4 3 2 1
    }
}

5. The while Loop #

fun main() {
    var counter = 5
    
    // The condition is checked BEFORE the loop runs
    while (counter > 0) {
        println("Countdown: $counter")
        counter-- // IMPORTANT: Must decrease the counter to avoid an infinite loop!
    }
    println("Liftoff!")
}

6. The do-while Loop #

fun main() {
    var x = 10
    
    do {
        println("x is $x")
        x++
    } while (x < 5) // Condition is false, but the block already ran once!
}

7. Loop Control (break and continue) #

• break: Instantly exits the entire loop.

• continue: Skips the rest of the current iteration and jumps to the next one.

fun main() {
    for (i in 1..10) {
        if (i == 3) {
            continue // Skips printing 3
        }
        if (i == 7) {
            break // Stops the loop completely when i reaches 7
        }
        println(i)
    }
    // Output: 1, 2, 4, 5, 6
}

8. Mini Project: Multiplication Table Generator #

fun main() {
    print("Enter a number to generate its table: ")
    val number = readln().toIntOrNull() ?: 1

    println("--- Multiplication Table for $number ---")
    
    for (i in 1..10) {
        val result = number * i
        println("$number x $i = $result")
    }
}

9. Common Mistakes #

• Infinite Loops: Forgetting to increment or decrement the condition variable inside a while loop. The program will run forever and crash your computer!

• Using Java for syntax: Trying to write for (int i=0; i<10; i++) in Kotlin will result in compilation errors.

10. Best Practices #

• Prefer for loops: If you are iterating over a known set of numbers or a list, always use a for loop with a Range. Only use while loops for unbounded operations (like waiting for a user to type a specific word).

11. Exercises #

1. 1. Write a for loop that prints the even numbers between 2 and 20 (use step).

1. 2. Write a while loop that starts at x = 0, adds 5 to x each iteration, and stops when x reaches 25.

12. MCQs with Answers #

13. Interview Questions #

• Q: What is an Infinite Loop, and how does it occur in a while statement?

• Q: Explain the difference between the break and continue statements. Give an example of when you would use each.

14. Summary #

15. Next Chapter Recommendation #