For loop with ranges in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Kotlin

for (i in [1]) {
    println(i)
}

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

A1 until 5

B1..5

C5..1

D5 until 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'until' which excludes the end number.

Reversing the range like '5..1' which does not work as expected.

The range 1..5 includes numbers from 1 to 5 inclusive.

2fill in blank

medium

Complete the code to print numbers from 1 up to but not including 5.

Kotlin

for (i in [1]) {
    println(i)
}

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

A1 until 5

B1..5

C0 until 5

D5 downTo 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using '..' which includes the end number.

Using a reversed range which does not print anything.

The until operator creates a range excluding the end value, so 1 until 5 is 1, 2, 3, 4.

3fill in blank

hard

Fix the error in the for loop to count down from 5 to 1.

Kotlin

for (i in [1]) {
    println(i)
}

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

A5 downTo 1

B5..1

C1 downTo 5

D1..5

Attempts:

3 left

💡 Hint

Common Mistakes

Using '..' with reversed numbers which does not work.

Using 'downTo' with start less than end.

The downTo function creates a decreasing range from 5 down to 1.

4fill in blank

hard

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

Kotlin

for (i in [1] step [2]) {
    println(i)
}

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

A2..10

B1..10

C2

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using step 3 which skips numbers incorrectly.

Starting range at 1 which includes odd numbers.

The range 2..10 includes numbers from 2 to 10, and step 2 makes the loop jump by 2, printing even numbers.

5fill in blank

hard

Fill all three blanks to create a for loop that prints numbers from 10 down to 1, stepping by 2.

Kotlin

for (i in [1] downTo [2] step [3]) {
    println(i)
}

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

A1

BdownTo

C2

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'until' instead of 'downTo' for counting down.

Using step 1 which does not skip numbers.

The loop starts at 10, counts down to 1 using downTo, and steps by 2 to skip every other number.

Practice

1. What does the following Kotlin code do?
for (i in 1..5) { println(i) }

easy

A. Prints numbers from 1 to 4

B. Prints numbers from 1 to 5 inclusive

C. Prints numbers from 0 to 5

D. Prints numbers from 5 down to 1

Solution

1. Step 1: Understand the range operator

   The operator 1..5 creates a range including numbers 1, 2, 3, 4, and 5.

2. Step 2: Loop through the range

   The for loop runs from 1 to 5, printing each number.

3. Final Answer:

   Prints numbers from 1 to 5 inclusive -> Option B

4. Quick Check:

   Range 1..5 includes 5 [OK]

Hint: .. means inclusive range from start to end [OK]

Common Mistakes:

• Thinking .. excludes the last number
• Confusing range with step or downTo
• Assuming it counts down automatically

2. Which of the following is the correct syntax for a for loop counting down from 5 to 1 in Kotlin?

easy

A. for (i in 5 downTo 1) { println(i) }

B. for (i in 1..5 step -1) { println(i) }

C. for (i in 5..1) { println(i) }

D. for (i in 1 downTo 5) { println(i) }

Solution

1. Step 1: Identify correct descending range syntax

   Kotlin uses downTo to count down from a higher number to a lower number.

2. Step 2: Check each option

   for (i in 5 downTo 1) { println(i) } uses 5 downTo 1, which is correct. for (i in 5..1) { println(i) } uses an invalid range (5..1). for (i in 1..5 step -1) { println(i) } tries to use negative step incorrectly. for (i in 1 downTo 5) { println(i) } reverses the range incorrectly.

3. Final Answer:

   for (i in 5 downTo 1) { println(i) } -> Option A

4. Quick Check:

   Use downTo for descending loops [OK]

Hint: Use downTo to count down in Kotlin loops [OK]

Common Mistakes:

• Using .. for descending ranges
• Trying negative step with .. (not allowed)
• Swapping start and end in downTo

3. What is the output of this Kotlin code?

var sum = 0
for (i in 1..5 step 2) {
  sum += i
}
println(sum)

medium

A. 6

B. 15

C. 9

D. 10

Solution

1. Step 1: Understand the loop range and step

   The loop runs from 1 to 5, stepping by 2: values are 1, 3, 5.

2. Step 2: Calculate the sum of these values

   sum = 0 + 1 + 3 + 5 = 9

3. Final Answer:

   9 -> Option C

4. Quick Check:

   1 + 3 + 5 = 9 [OK]

Hint: Add numbers in steps to find sum quickly [OK]

Common Mistakes:

• Adding all numbers 1 to 5 instead of stepping
• Using step as a multiplier
• Confusing step with downTo

4. Find the error in this Kotlin code snippet:

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

medium

A. println cannot be used inside for loop

B. step cannot be used with ranges

C. Variable i is not declared

D. Range 10..1 is invalid for counting down

Solution

1. Step 1: Analyze the range 10..1

   The range 10..1 tries to count up from 10 to 1, which is invalid because 10 is greater than 1.

2. Step 2: Understand correct descending syntax

   To count down, use downTo instead of .., e.g., 10 downTo 1 step 2.

3. Final Answer:

   Range 10..1 is invalid for counting down -> Option D

4. Quick Check:

   Use downTo for descending ranges [OK]

Hint: .. always counts up; use downTo to count down [OK]

Common Mistakes:

• Using .. for descending ranges
• Thinking step fixes descending range
• Ignoring Kotlin's range direction rules

5. You want to print all even numbers from 2 to 20 inclusive using a for loop in Kotlin. Which code snippet correctly does this?

hard

A. for (i in 2..20 step 2) { println(i) }

B. for (i in 2..19) { if (i % 2 == 0) println(i) }

C. for (i in 2 downTo 20 step 2) { println(i) }

D. for (i in 1..10 step 2) { println(i * 2) }

Solution

1. Step 1: Identify the range and step for even numbers

   Even numbers from 2 to 20 can be generated by starting at 2 and stepping by 2 up to 20.

2. Step 2: Check each option

   for (i in 2..20 step 2) { println(i) } uses 2..20 step 2, which prints 2,4,6,...,20 correctly. for (i in 2..19) { if (i % 2 == 0) println(i) } ends at 19 so prints evens up to 18, missing 20. for (i in 2 downTo 20 step 2) { println(i) } counts down incorrectly. for (i in 1..10 step 2) { println(i * 2) } prints 2,6,10,..., not all even numbers.

3. Final Answer:

   for (i in 2..20 step 2) { println(i) } -> Option A

4. Quick Check:

   Use step 2 from 2 to 20 for evens [OK]

Hint: Use step 2 starting at 2 to print even numbers [OK]

Common Mistakes:

• Using downTo instead of .. for ascending
• Forgetting to step by 2
• Multiplying inside loop incorrectly