while True pattern in Python - Mini Project: Build & Apply

Using the while True Pattern in Python

📖 Scenario: You are creating a simple program that keeps asking a user to enter a number until they type 0. This is like asking a friend to keep giving you numbers until they say stop.

🎯 Goal: Build a program that uses the while True pattern to repeatedly ask for numbers and stops when the user enters 0.

📋 What You'll Learn

Create a variable to store user input

Use a while True loop to keep asking for input

Use an if statement to check if the input is 0

Use break to exit the loop when input is 0

Print a message when the loop ends

💡 Why This Matters

🌍 Real World

This pattern is useful when you want to keep asking for information until the user decides to stop, like filling a form or entering commands.

💼 Career

Understanding the <code>while True</code> loop and <code>break</code> is important for writing programs that need continuous input or repeated checks, common in many software jobs.

1

Create a variable to store user input

Create a variable called user_input and set it to an empty string "".

Python

# Create a variable called user_input and set it to an empty string ""
# Your code here

Hint

Think of user_input as a box where you will keep the number the user types.

2

Set up a while True loop to ask for input

Write a while True loop that asks the user to enter a number using input() and stores it in user_input.

Python

user_input = ""
# Write a while True loop that asks for input and stores it in user_input
# Your code here

Hint

Use while True: to create an endless loop. Inside it, use input() to get the number.

3

Add a condition to stop the loop when input is 0

Inside the while True loop, add an if statement to check if user_input is equal to "0". If yes, use break to exit the loop.

Python

user_input = ""
while True:
    user_input = input("Enter a number (0 to stop): ")
    # Add if statement to check if user_input is "0" and break the loop
    # Your code here

Hint

Use if user_input == "0": to check the input. Use break to stop the loop.

4

Print a message after the loop ends

After the while True loop, write a print statement to display "Loop ended because you entered 0.".

Python

user_input = ""
while True:
    user_input = input("Enter a number (0 to stop): ")
    if user_input == "0":
        break
# Print the message after the loop ends
# Your code here

Hint

Use print("Loop ended because you entered 0.") after the loop to show the message.

Practice

1.

What does the while True loop do in Python?

easy

A. It creates a loop that runs forever unless stopped by break.

B. It runs the loop only once.

C. It runs the loop a fixed number of times.

D. It causes a syntax error.

Solution

1. Step 1: Understand the meaning of while True

   The condition True is always true, so the loop will keep running forever.

2. Step 2: Recognize how to stop the loop

   To stop this infinite loop, a break statement is used inside the loop when a condition is met.

3. Final Answer:

   It creates a loop that runs forever unless stopped by break. -> Option A

4. Quick Check:

   while True = infinite loop until break [OK]

Hint: Remember: while True loops forever until break stops it [OK]

Common Mistakes:

• Thinking it runs only once
• Assuming it runs a fixed number of times
• Believing it causes a syntax error

2.

Which of the following is the correct syntax to stop a while True loop when a variable count reaches 5?

count = 0
while True:
    count += 1
    ?

easy

A. if count == 5: break

B. if count = 5: break

C. if count == 5: continue

D. if count > 5: stop

Solution

1. Step 1: Identify correct comparison operator

   Use == to compare values, so if count == 5 is correct.

2. Step 2: Use break to exit the loop

   The break statement stops the loop immediately when the condition is true.

3. Final Answer:

   if count == 5: break -> Option A

4. Quick Check:

   Use == and break to stop loop [OK]

Hint: Use double equals (==) for comparison and break to stop [OK]

Common Mistakes:

• Using single equals (=) instead of double equals (==)
• Using continue instead of break
• Using undefined commands like stop

3.

What will be the output of the following code?

i = 0
while True:
    i += 2
    if i > 6:
        break
print(i)

medium

A. 0

B. 6

C. 4

D. 8

Solution

1. Step 1: Trace the loop increments

   i starts at 0, then increases by 2 each loop: 2, 4, 6, 8.

2. Step 2: Check the break condition

   The loop breaks when i > 6, which happens when i becomes 8.

3. Final Answer:

   6 -> Option B

4. Quick Check:

   Loop stops at i=8 because 8 > 6, but the printed value is the last before break, which is 6 [OK]

Hint: Add increments step-by-step until break condition met [OK]

Common Mistakes:

• Stopping at i=6 instead of i=8
• Printing before break
• Confusing break condition with >= instead of >

4.

Find the error in this code snippet:

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

medium

A. Wrong comparison operator in if count == 3

B. Incorrect indentation of count += 1

C. Missing break statement

D. Missing colon after while True

Solution

1. Step 1: Check syntax of while statement

   Python requires a colon (:) after while True to start the loop block.

2. Step 2: Verify other parts

   Indentation and comparison operator are correct; break is present.

3. Final Answer:

   Missing colon after while True -> Option D

4. Quick Check:

   Loops need colon after condition [OK]

Hint: Look for missing colons after loop or if statements [OK]

Common Mistakes:

• Forgetting colon after while
• Misaligning indentation
• Confusing = and == in conditions

5.

You want to write a program that keeps asking the user to enter a number until they enter a negative number. Which code snippet correctly uses while True to do this?

hard

A. while num >= 0:
num = int(input('Enter number: '))
print(f'You entered {num}')

B. while True:
num = int(input('Enter number: '))
if num > 0:
break
print(f'You entered {num}')

C. while True:
num = int(input('Enter number: '))
if num < 0:
break
print(f'You entered {num}')

D. while True:
num = input('Enter number: ')
if num < 0:
break

Solution

1. Step 1: Check loop condition and input

   while True: num = int(input('Enter number: ')) if num < 0: break print(f'You entered {num}') uses while True and asks for input inside the loop, converting it to int.

2. Step 2: Verify break condition and output

   It breaks when the number is negative (< 0) and prints the number otherwise.

3. Final Answer:

   while True: num = int(input('Enter number: ')) if num < 0: break print(f'You entered {num}') -> Option C

4. Quick Check:

   Break on negative input inside infinite loop [OK]

Hint: Break loop when negative number entered, print otherwise [OK]

Common Mistakes:

• Breaking on wrong condition (positive instead of negative)
• Not converting input to int
• Missing print statement or break