While loop execution flow in Python - Mini Project: Build & Apply

While Loop Execution Flow

📖 Scenario: You are helping a cashier count the number of customers entering a small shop. The cashier wants to keep track until a certain number is reached.

🎯 Goal: Build a program that uses a while loop to count customers until the target number is reached.

📋 What You'll Learn

Create a variable to store the current count of customers.

Create a variable for the target number of customers.

Use a while loop to increase the count until it reaches the target.

Print the final count after the loop ends.

💡 Why This Matters

🌍 Real World

Counting customers or items until a goal is reached is common in stores, events, or inventory management.

💼 Career

Understanding while loops helps in automating repetitive tasks and controlling program flow in many software jobs.

1

Create the initial count variable

Create a variable called customer_count and set it to 0.

Python

# Create a variable called customer_count and set it to 0
# Your code here

Hint

Think of customer_count as the number of customers counted so far.

2

Set the target number of customers

Create a variable called target_customers and set it to 5.

Python

customer_count = 0
# Create a variable called target_customers and set it to 5
# Your code here

Hint

This is the number of customers we want to count until.

3

Use a while loop to count customers

Use a while loop with the condition customer_count < target_customers. Inside the loop, increase customer_count by 1.

Python

customer_count = 0
target_customers = 5
# Use a while loop to increase customer_count until it reaches target_customers
# Your code here

Hint

The loop runs as long as customer_count is less than target_customers.

4

Print the final customer count

Write a print statement to display the text "Total customers: " followed by the value of customer_count.

Python

customer_count = 0
target_customers = 5
while customer_count < target_customers:
    customer_count += 1
# Print the final customer_count
# Your code here

Hint

Use a comma in print to separate text and variable.

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