While and do-while loops in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a while loop with decrement

What is the output of this Kotlin code snippet?

Kotlin

var x = 3
while (x > 0) {
    print(x)
    x--
}

A 123

B 321

C 3

D 0

💡 Hint

Remember that the loop runs while x is greater than zero and x decreases each time.

The loop prints x starting from 3 down to 1, so the output is '321'.

❓ Predict Output

intermediate

Output of a do-while loop with increment

What will this Kotlin code print?

Kotlin

var count = 0
do {
    print(count)
    count += 2
} while (count < 5)

A 024

B 0246

C 02

D 0

💡 Hint

The loop runs at least once and increments count by 2 each time.

The loop prints 0, then increments count to 2, prints 2, increments to 4, prints 4, then increments to 6 and stops because 6 is not less than 5.

🔧 Debug

advanced

Identify the error in this while loop

What error does this Kotlin code produce?

Kotlin

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

A Infinite loop (no increment of i)

B Syntax error: missing parentheses

C Type error: i is not an integer

D No error, prints 0 1 2

💡 Hint

Check if the loop variable changes inside the loop.

The variable i is never incremented, so the condition i < 3 is always true, causing an infinite loop.

❓ Predict Output

advanced

Output of nested while and do-while loops

What is the output of this Kotlin code?

Kotlin

var a = 1
while (a <= 2) {
    var b = 1
    do {
        print(a * b)
        b++
    } while (b <= 2)
    a++
}

A 124

B 1122

C 1224

D 2244

💡 Hint

The outer loop runs twice, and the inner loop runs twice each time.

For a=1, b=1 and 2 print 1 and 2; for a=2, b=1 and 2 print 2 and 4; combined output is '1224'.

🧠 Conceptual

expert

Difference between while and do-while loops

Which statement correctly describes the difference between while and do-while loops in Kotlin?

A While loops can only count up; do-while loops can only count down.

B A while loop runs the body once before checking the condition; a do-while loop checks the condition first.

C Both loops check the condition before running the body, but do-while loops run faster.

D A while loop checks the condition before running the loop body; a do-while loop runs the body once before checking the condition.

💡 Hint

Think about when the condition is checked in each loop type.

While loops test the condition before running the loop body, so they may not run at all. Do-while loops run the body first, then test the condition, so they always run at least once.