Counter-based while loop in Python - Mini Project: Build & Apply

Counter-based while loop

📖 Scenario: You are helping a small shop owner count the number of customers who entered the shop during the day. The owner wants to keep track of the count using a simple program.

🎯 Goal: Build a Python program that uses a counter-based while loop to count customers up to a certain number.

📋 What You'll Learn

Create a counter variable to keep track of the number of customers

Create a maximum number variable to set the limit of customers to count

Use a while loop that runs until the counter reaches the maximum number

Print the final count of customers

💡 Why This Matters

🌍 Real World

Counting customers or items is common in shops, events, or any place where tracking numbers is important.

💼 Career

Understanding loops and counters is essential for programming tasks like data processing, automation, and monitoring systems.

1

Create the initial counter variable

Create a variable called customer_count and set it to 0 to start counting customers.

Python

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

Hint

Think of customer_count as a box where you keep adding one for each customer.

2

Set the maximum number of customers

Create a variable called max_customers and set it to 5 to limit the count.

Python

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

Hint

This number tells the program when to stop counting.

3

Write the counter-based while loop

Use a while loop with the condition customer_count < max_customers. Inside the loop, increase customer_count by 1 each time.

Python

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

Hint

The loop keeps adding one to customer_count until it equals max_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
max_customers = 5
while customer_count < max_customers:
    customer_count += 1
# Print the total number of customers
# Your code here

Hint

Use a comma in the print statement to join text and the number.

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