While and do-while loops in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers from 1 to 5 using a while loop.

Kotlin

var i = 1
while (i [1] 5) {
    println(i)
    i++
}

Drag options to blanks, or click blank then click option'

A<=

B<

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'i < 5' will stop before printing 5.

Using 'i > 5' will never enter the loop.

The while loop continues as long as i is less than or equal to 5, so it prints numbers 1 to 5.

2fill in blank

medium

Complete the code to print numbers from 1 to 5 using a do-while loop.

Kotlin

var i = 1
do {
    println(i)
    i++
} while (i [1] 6)

Drag options to blanks, or click blank then click option'

A<

B>

C<=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' will print 6 as well.

Using '>' will cause the loop to run only once or not at all.

The do-while loop runs at least once and continues while i is less than 6, printing 1 to 5.

3fill in blank

hard

Fix the error in the while loop condition to avoid an infinite loop.

Kotlin

var count = 0
while (count [1] 5) {
    println(count)
    // Missing increment
}

Drag options to blanks, or click blank then click option'

A<=

B>=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>=' or '>' will cause the loop to never run or run infinitely.

Not incrementing the counter causes infinite loop.

The condition should be count < 5 to run the loop 5 times. However, the loop will still be infinite because count is not incremented inside the loop.

4fill in blank

hard

Fill both blanks to create a while loop that prints even numbers from 2 to 10.

Kotlin

var num = 2
while (num [1] 10) {
    println(num)
    num [2] 2
}

Drag options to blanks, or click blank then click option'

A<=

B+=

C-=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' will exclude 10.

Using '-=' will decrease num and cause infinite loop.

The loop runs while num is less than or equal to 10, and increments num by 2 each time to print even numbers.

5fill in blank

hard

Fill all three blanks to create a do-while loop that prints numbers from 10 down to 1.

Kotlin

var i = [1]
do {
    println(i)
    i [2] 1
} while (i [3] 0)

Drag options to blanks, or click blank then click option'

A10

B-=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at 1 will print only one number.

Using '+=' will increase i and cause infinite loop.

Using '<' in condition will cause infinite loop.

The loop starts at 10, decreases i by 1 each time, and continues while i is greater than 0, printing 10 down to 1.

Practice

1. What is the main difference between a while loop and a do-while loop in Kotlin?

easy

A. while loops are faster than do-while loops.

B. while runs code once before checking; do-while checks the condition before running code.

C. while checks the condition before running the code; do-while runs code once before checking.

D. while loops only run once; do-while loops run multiple times.

Solution

1. Step 1: Understand while loop behavior

   A while loop checks its condition before running the code inside it, so if the condition is false initially, the code inside won't run at all.

2. Step 2: Understand do-while loop behavior

   A do-while loop runs the code inside once first, then checks the condition to decide if it should repeat.

3. Final Answer:

   while checks the condition before running the code; do-while runs code once before checking. -> Option C

4. Quick Check:

   Loop condition check timing = while checks the condition before running the code; do-while runs code once before checking. [OK]

Hint: Remember: do-while runs code once before condition check [OK]

Common Mistakes:

• Thinking both loops check condition before running code
• Confusing which loop runs code first
• Assuming do-while runs only once

2. Which of the following is the correct syntax for a do-while loop in Kotlin?

easy

A. do { /* code */ } while (condition)

B. while (condition) { /* code */ } do

C. do (condition) { /* code */ } while

D. while { /* code */ } do (condition)

Solution

1. Step 1: Recall correct do-while syntax

   The do-while loop syntax starts with do, then the code block in braces, followed by while with the condition in parentheses.

2. Step 2: Compare options to syntax

   do { /* code */ } while (condition) matches the correct syntax exactly: do { /* code */ } while (condition). Others have wrong order or misplaced keywords.

3. Final Answer:

   do { /* code */ } while (condition) -> Option A

4. Quick Check:

   Syntax order for do-while = do { /* code */ } while (condition) [OK]

Hint: Remember: do { } while(condition) is the correct order [OK]

Common Mistakes:

• Placing while before do
• Using parentheses incorrectly
• Mixing up braces and parentheses

3. What will be the output of this Kotlin code?

var count = 3
while (count > 0) {
    println(count)
    count--
}

medium

A. 3 2 1

B. 1 2 3

C. 3 2 1 0

D. 0 1 2 3

Solution

1. Step 1: Analyze initial value and condition

   The variable count starts at 3. The loop runs while count > 0, so it runs for 3, 2, and 1.

2. Step 2: Trace each iteration and output

   Each loop prints the current count then decreases it by 1. So it prints 3, then 2, then 1, then stops before printing 0.

3. Final Answer:

   3 2 1 -> Option A

4. Quick Check:

   Loop prints count down from 3 to 1 = 3 2 1 [OK]

Hint: Count down loops print from start to 1, not zero [OK]

Common Mistakes:

• Including 0 in output
• Printing in ascending order
• Not decrementing count

4. Identify the error in this Kotlin code snippet:

var i = 1
do {
    println(i)
    i++
} while i <= 3

medium

A. Missing braces around the do block

B. Incorrect use of do keyword

C. Variable i should be declared inside the loop

D. Missing parentheses around the while condition

Solution

1. Step 1: Check do-while syntax

   The while condition must be inside parentheses after the while keyword.

2. Step 2: Identify the error in the code

   The code has while i <= 3 without parentheses. It should be while (i <= 3).

3. Final Answer:

   Missing parentheses around the while condition -> Option D

4. Quick Check:

   Parentheses required for while condition = Missing parentheses around the while condition [OK]

Hint: Always put condition in parentheses after while [OK]

Common Mistakes:

• Omitting parentheses in while condition
• Placing variable declaration inside loop unnecessarily
• Confusing braces and parentheses

5. You want to write a Kotlin program that asks the user to enter a positive number and keeps asking until the user enters a number greater than zero. Which loop should you use and why?

hard

A. Use a while loop because it checks the condition before asking the user.

B. Use a do-while loop because it asks the user at least once before checking the condition.

C. Use a while loop because it runs the code at least once.

D. Use a do-while loop because it never checks the condition.

Solution

1. Step 1: Understand the problem requirement

   The program must ask the user at least once to enter a number, then repeat if the number is not positive.

2. Step 2: Choose the correct loop type

   A do-while loop runs the code block once before checking the condition, so it ensures the user is asked at least once.

3. Final Answer:

   Use a do-while loop because it asks the user at least once before checking the condition. -> Option B

4. Quick Check:

   Ask user once then check = do-while loop = Use a do-while loop because it asks the user at least once before checking the condition. [OK]

Hint: Use do-while to run code once before condition check [OK]

Common Mistakes:

• Choosing while loop which may skip asking once
• Thinking do-while never checks condition
• Confusing loop behavior with input requirements