Counter-based while loop in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Python

count = 1
while count [1] 5:
    print(count)
    count += 1

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

A>=

B<

C>

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'count < 5' which stops before printing 5.

Using 'count > 5' which never runs the loop.

The condition count <= 5 ensures the loop runs while count is 1 through 5.

2fill in blank

medium

Complete the code to count down from 10 to 1 using a while loop.

Python

num = 10
while num [1] 0:
    print(num)
    num -= 1

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

A>=

B>

C<

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'num >= 0' which would print 0 as well.

Using 'num < 0' which never runs the loop.

The condition num > 0 runs the loop while num is greater than zero, counting down to 1.

3fill in blank

hard

Fix the error in the code to print even numbers from 2 to 10 using a while loop.

Python

i = 2
while i [1] 10:
    print(i)
    i += 2

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

A<=

B<

C>=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'i < 10' which stops before printing 10.

Using 'i > 10' which never runs the loop.

The condition i <= 10 ensures the loop includes 10 in the output.

4fill in blank

hard

Fill both blanks to create a while loop that prints numbers from 3 to 7.

Python

num = 3
while num [1] 7:
    print(num)
    num [2] 1

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

A<=

B-=

C+=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '<=' which excludes 7.

Using '-=' which decreases the counter and causes an infinite loop.

The loop runs while num <= 7 and increases num by 1 each time with num += 1.

5fill in blank

hard

Fill all three blanks to create a while loop that prints odd numbers from 1 to 9.

Python

n = 1
while n [1] 9:
    print(n)
    n [2] [3]

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

A<=

B+=

C2

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '<=' which excludes 9.

Using '-' instead of '+=' which decreases the counter.

Using 1 instead of 2 which prints every number, not just odd.

The loop runs while n <= 9, and increases n by 2 each time with n += 2 to print odd numbers.

Practice

1.

What is the main purpose of a counter in a while loop?

easy

A. To keep track of how many times the loop has run

B. To store the final result of the loop

C. To stop the program immediately

D. To print messages inside the loop

Solution

1. Step 1: Understand the role of a counter

   A counter is a variable that counts how many times the loop runs.

2. Step 2: Identify the purpose in a while loop

   The counter helps the loop know when to stop by checking its value in the condition.

3. Final Answer:

   To keep track of how many times the loop has run -> Option A

4. Quick Check:

   Counter tracks loop runs = D [OK]

Hint: Counter counts loop repeats to control stopping [OK]

Common Mistakes:

• Thinking counter stores final result
• Confusing counter with printing inside loop
• Believing counter stops program immediately

2.

Which of the following is the correct syntax to start a counter at 0 before a while loop?

?

easy

A. counter := 0

B. while counter = 0:

C. counter == 0

D. counter = 0

Solution

1. Step 1: Identify correct variable assignment

   To start a counter, assign 0 using a single equal sign: counter = 0.

2. Step 2: Check other options for syntax errors

   while counter = 0: uses assignment in while condition (invalid), C uses comparison, D uses walrus operator incorrectly here.

3. Final Answer:

   counter = 0 -> Option D

4. Quick Check:

   Assign counter with = 0 before loop = A [OK]

Hint: Use single = to assign counter before loop [OK]

Common Mistakes:

• Using == instead of = for assignment
• Trying to assign inside while condition
• Confusing walrus operator usage

3.

What will be the output of this code?

counter = 1
while counter <= 3:
    print(counter)
    counter += 1

medium

A. 1 2 3

B. 1 2 3 4

C. 0 1 2 3

D. 3 2 1

Solution

1. Step 1: Trace the loop iterations

   Counter starts at 1, prints 1, then increments to 2, prints 2, increments to 3, prints 3, then increments to 4.

2. Step 2: Check loop condition

   Loop stops when counter is 4 because 4 <= 3 is false. So printed numbers are 1, 2, 3.

3. Final Answer:

   1 2 3 -> Option A

4. Quick Check:

   Prints 1 to 3 with counter increment = C [OK]

Hint: Loop runs while counter ≤ 3, prints 1,2,3 [OK]

Common Mistakes:

• Including 4 in output
• Starting count from 0 instead of 1
• Printing numbers in reverse

4.

Find the error in this code and choose the fix:

counter = 0
while counter < 5
    print(counter)
    counter += 1

medium

A. Change < to <= in the while condition

B. Initialize counter to 1 instead of 0

C. Add a colon ':' after the while condition

D. Remove the increment line inside the loop

Solution

1. Step 1: Identify syntax error in while loop

   The while statement is missing a colon ':' at the end of the condition line.

2. Step 2: Check other options

   Changing < to <= is not an error fix, initializing counter differently or removing increment causes logic errors.

3. Final Answer:

   Add a colon ':' after the while condition -> Option C

4. Quick Check:

   Missing colon causes syntax error = B [OK]

Hint: Always put ':' after while condition [OK]

Common Mistakes:

• Forgetting colon after while condition
• Changing loop logic instead of fixing syntax
• Removing counter increment causing infinite loop

5.

Write a counter-based while loop that prints only even numbers from 2 to 10 inclusive.

counter = 2
while counter <= 10:
    print(counter)
    ?

What should replace ? to correctly increment the counter?

hard

A. counter += 1

B. counter += 2

C. counter = counter * 2

D. counter -= 2

Solution

1. Step 1: Understand the goal

   We want to print even numbers from 2 to 10, so counter should increase by 2 each time.

2. Step 2: Choose correct increment

   Using counter += 2 moves counter from 2 to 4, 6, 8, 10 correctly.

3. Final Answer:

   counter += 2 -> Option B

4. Quick Check:

   Increment by 2 to print evens = A [OK]

Hint: Increase counter by 2 to get even numbers [OK]

Common Mistakes:

• Incrementing by 1 prints odd numbers too
• Multiplying counter causes wrong jumps
• Decrementing counter causes infinite loop