Infinite loop prevention in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to prevent an infinite loop by updating the loop variable.

Python

count = 0
while count < 5:
    print(count)
    count [1] 1

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

A+=

B-=

C*=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Using -= causes the count to decrease, leading to an infinite loop.

Using *= or /= changes the count unpredictably and may not stop the loop.

Using count += 1 increases the count each time, so the loop will eventually stop.

2fill in blank

medium

Complete the code to stop the loop when the user types 'exit'.

Python

while True:
    command = input('Enter command: ')
    if command [1] 'exit':
        break

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

A!=

B==

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using != causes the loop to break on any input except 'exit'.

Using < or > does not correctly compare strings for equality.

The loop breaks when the command is exactly 'exit', so we check if command == 'exit'.

3fill in blank

hard

Fix the error in the loop condition to prevent an infinite loop.

Python

i = 10
while i > 0:
    print(i)
    i [1] 1

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

A-=

B+=

C*=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Increasing i causes the loop to never end.

Multiplying or dividing i may not reach 0 and cause infinite loops.

Since i starts at 10 and the loop runs while i > 0, we must decrease i with i -= 1 to eventually stop the loop.

4fill in blank

hard

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

Python

num = 2
while num [1] 10:
    print(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 >= in the condition causes the loop to never run.

Using -= decreases the number and causes an infinite loop.

The loop runs while num <= 10 and increases num by 2 each time with num += 2 to print even numbers.

5fill in blank

hard

Fill all three blanks to create a loop that counts down from 5 to 1 and stops.

Python

counter = [1]
while counter [2] 0:
    print(counter)
    counter [3] 1

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

A5

B>

C-=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Starting counter at 0 causes the loop to never run.

Using < in the condition causes an infinite loop.

Increasing counter causes the loop to never end.

Start counter at 5, loop while counter > 0, and decrease it by 1 each time with counter -= 1.

Practice

1. What is the main reason an infinite loop happens in Python?

easy

A. The loop runs only once

B. The loop uses a break statement

C. The loop condition never becomes false

D. The loop has no variables

Solution

1. Step 1: Understand loop condition

   An infinite loop occurs when the condition controlling the loop never changes to false.

2. Step 2: Identify cause of infinite loop

   If the loop condition never becomes false, the loop keeps running forever.

3. Final Answer:

   The loop condition never becomes false -> Option C

4. Quick Check:

   Infinite loop = condition never false [OK]

Hint: Check if loop condition can ever become false [OK]

Common Mistakes:

• Thinking break causes infinite loops
• Assuming loops run only once cause infinite loops
• Ignoring the loop condition

2. Which of these loop structures correctly prevents an infinite loop?

easy

A. while True:
print('Hello')

B. while x < 5:
x += 1

C. while x == 0:
pass

D. while x > 0:
print(x)

Solution

1. Step 1: Check each loop's condition and body

   while True: print('Hello') loops forever because condition is always True with no break. while x < 5: x += 1 increases x, so condition will become false. while x == 0: pass loops forever because x never changes. while x > 0: print(x) loops forever because x is never changed.

2. Step 2: Identify loop that ends

   Only while x < 5: x += 1 changes x to eventually stop the loop.

3. Final Answer:

   while x < 5: x += 1 -> Option B

4. Quick Check:

   Change loop variable to end loop [OK]

Hint: Look for loops that update the condition variable [OK]

Common Mistakes:

• Choosing loops with constant True condition
• Ignoring variable updates inside loop
• Assuming print stops loops

3. What will be the output of this code?

i = 0
while i < 3:
    print(i)
    i -= 1

medium

A. SyntaxError

B. 0 1 2

C. 0

D. 0 -1 -2 ... (infinite loop)

Solution

1. Step 1: Analyze loop condition and variable change

   i starts at 0 and loop runs while i < 3. Inside loop, i decreases by 1 each time.

2. Step 2: Determine if loop ends

   Since i decreases, it will go 0, -1, -2, ... always less than 3, so loop never ends.

3. Final Answer:

   0 -1 -2 ... (infinite loop) -> Option D

4. Quick Check:

   Variable moves away from exit condition = infinite loop [OK]

Hint: Check if loop variable moves toward or away from condition [OK]

Common Mistakes:

• Assuming i increases automatically
• Thinking loop stops after first print
• Confusing syntax errors with logic errors

4. Find the error that causes an infinite loop in this code:

count = 5
while count > 0:
    print(count)

medium

A. Missing decrement of count

B. Missing increment of count

C. Wrong comparison operator

D. Syntax error in while statement

Solution

1. Step 1: Check loop condition and body

   The loop runs while count > 0, but count is never changed inside the loop.

2. Step 2: Identify missing update

   Without decreasing count, the condition stays true forever, causing infinite loop.

3. Final Answer:

   Missing decrement of count -> Option A

4. Quick Check:

   Loop variable must change to end loop [OK]

Hint: Look for missing variable update inside loop [OK]

Common Mistakes:

• Thinking increment needed instead of decrement
• Assuming loop ends automatically
• Confusing syntax errors with logic errors

5. You want to print numbers from 1 to 5 using a while loop without causing an infinite loop. Which code correctly does this?

hard

A. num = 1
while num <= 5:
print(num)
num += 1

B. num = 5
while num > 0:
print(num)
num += 1

C. num = 1
while num < 5:
print(num)
num -= 1

D. num = 1
while num <= 5:
print(num)

Solution

1. Step 1: Check loop conditions and variable updates

   num = 1 while num <= 5: print(num) never changes num, so infinite loop. num = 1 while num <= 5: print(num) num += 1 increases num, stopping at 6. num = 1 while num < 5: print(num) num -= 1 decreases num, moving away from stop condition. num = 5 while num > 0: print(num) num += 1 increases num starting at 5, so loop never ends.

2. Step 2: Confirm correct loop behavior

   Only num = 1 while num <= 5: print(num) num += 1 prints 1 to 5 and stops correctly.

3. Final Answer:

   num = 1 while num <= 5: print(num) num += 1 -> Option A

4. Quick Check:

   Update loop variable toward exit condition [OK]

Hint: Ensure loop variable moves toward stopping condition [OK]

Common Mistakes:

• Forgetting to update loop variable
• Updating variable in wrong direction
• Using wrong loop condition