While loop execution flow in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple while loop

What is the output of this code?

Python

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

A

1
2
3

B

0
1
2
3

C

0
1
2

D

0
1
2
3
4

💡 Hint

Remember the loop runs while the condition is true, and stops when it becomes false.

The loop starts with i=0 and runs while i is less than 3. It prints 0, then 1, then 2. When i becomes 3, the condition fails and the loop stops.

❓ Predict Output

intermediate

While loop with break statement

What is the output of this code?

Python

count = 0
while True:
    print(count)
    count += 1
    if count == 3:
        break

A

0
1
2

B

0
1
2
3

C

1
2
3

D

0
1
2
3
4

💡 Hint

The break stops the loop when count reaches 3.

The loop prints count starting at 0. When count reaches 3, the break stops the loop before printing 3.

❓ Predict Output

advanced

While loop with else clause

What is the output of this code?

Python

i = 0
while i < 3:
    print(i)
    i += 1
else:
    print('Done')

A

0
1
2
Done

B

0
1
2

C Done

D

0
1
2
3
Done

💡 Hint

The else block runs after the while loop finishes normally.

The loop prints 0, 1, 2. After the loop ends because the condition is false, the else block prints 'Done'.

❓ Predict Output

advanced

While loop with continue statement

What is the output of this code?

Python

i = 0
while i < 5:
    i += 1
    if i == 3:
        continue
    print(i)

A

1
2
3
4
5

B

2
3
4
5

C

1
2
5

D

1
2
4
5

💡 Hint

The continue skips printing when i is 3.

The loop increments i first. When i is 3, continue skips the print. So 3 is not printed. Others are printed.

🧠 Conceptual

expert

Understanding infinite loops

Which option will cause an infinite loop when run?

A

i = 0
while i < 5:
    print(i)
    i += 1

B

i = 0
while i != 5:
    print(i)

C

i = 0
while i < 5:
    print(i)
    i += 2

D

while True:
    print('Hello')
    break

💡 Hint

Check if the loop variable changes so the condition can become false.

Option B never changes i, so i stays 0 and the condition i != 5 is always true, causing an infinite loop.

Practice

1.

What does a while loop do in Python?

easy

A. Stops the program immediately

B. Runs code only once

C. Repeats code as long as a condition is true

D. Runs code a fixed number of times

Solution

1. Step 1: Understand the purpose of a while loop

   A while loop runs repeatedly while its condition is true.

2. Step 2: Compare options with this behavior

   Only Repeats code as long as a condition is true describes repeating code while a condition is true.

3. Final Answer:

   Repeats code as long as a condition is true -> Option C

4. Quick Check:

   While loop = repeat while true [OK]

Hint: While loops run repeatedly while condition is true [OK]

Common Mistakes:

• Thinking while loops run a fixed number of times
• Confusing while with if statement
• Believing while loops run only once

2.

Which of the following is the correct syntax to start a while loop in Python?

?

easy

A. while x > 0:

B. while (x > 0)

C. while x > 0 {}

D. while x > 0 then

Solution

1. Step 1: Recall Python while loop syntax

   Python uses a colon after the condition and no parentheses or braces.

2. Step 2: Match options with correct syntax

   while x > 0: uses 'while x > 0:' which is correct syntax.

3. Final Answer:

   while x > 0: -> Option A

4. Quick Check:

   Colon ends while condition line [OK]

Hint: Use colon after condition, no braces or 'then' [OK]

Common Mistakes:

• Adding braces {} like other languages
• Using 'then' keyword
• Putting condition in parentheses unnecessarily

3.

What will be the output of this code?

count = 3
while count > 0:
    print(count)
    count -= 1
print("Done")

medium

A. Done

B. 3 2 1 Done

C. 3 2 1 0 Done

D. 3 2 1 2 Done

Solution

1. Step 1: Trace the while loop iterations

   count starts at 3, prints 3, then decreases to 2, prints 2, then 1, then stops when count is 0.

2. Step 2: Note the final print after loop

   After loop ends, "Done" is printed.

3. Final Answer:

   3 2 1 Done -> Option B

4. Quick Check:

   Prints 3,2,1 then Done [OK]

Hint: Count decreases before loop ends, stops at zero [OK]

Common Mistakes:

• Expecting 0 to print inside loop
• Forgetting to decrease count
• Thinking loop runs forever

4.

Find the error in this code snippet:

i = 1
while i < 5
    print(i)
    i += 1

medium

A. Missing colon after while condition

B. Variable i is not initialized

C. Indentation error in print statement

D. Infinite loop because i never changes

Solution

1. Step 1: Check while loop syntax

   The while line must end with a colon (:).

2. Step 2: Identify the missing colon

   The code misses ':' after 'while i < 5', causing syntax error.

3. Final Answer:

   Missing colon after while condition -> Option A

4. Quick Check:

   While line needs colon [OK]

Hint: Always put colon after while condition [OK]

Common Mistakes:

• Forgetting colon after while
• Misindenting inside loop
• Not updating loop variable

5.

Consider this code:

n = 5
result = 1
while n > 1:
    result *= n
    n -= 1
print(result)

What does this code calculate?

hard

A. Sum of numbers from 1 to 5

B. Infinite loop with no output

C. Product of numbers from 1 to 4

D. Factorial of 5 (5!)

Solution

1. Step 1: Understand the loop's multiplication

   result multiplies by n each time, starting at 5 down to 2.

2. Step 2: Recognize factorial pattern

   Multiplying 5*4*3*2*1 equals 5 factorial (5!).

3. Final Answer:

   Factorial of 5 (5!) -> Option D

4. Quick Check:

   Multiplying down to 1 = factorial [OK]

Hint: Multiplying down from n to 1 calculates factorial [OK]

Common Mistakes:

• Thinking it sums numbers instead of multiplies
• Stopping multiplication at 2 instead of 1
• Assuming infinite loop