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Practice

Controlling Loops with the while Statement

The while statement is a construct that repeats a block of code as long as a given condition is True.

The loop terminates when the condition becomes False.

This makes the while loop useful for tasks that need to repeat until a specific condition is met, such as receiving user input.


Basic Structure of the while Loop​

A while loop executes the block of code following the colon (:) repeatedly as long as the condition remains true.

Basic Structure of the while Loop
while condition:
    code_to_execute

Since the code will repeat infinitely while the condition is true, you must include code that makes the condition false at some point.


Example: Printing Numbers from 1 to 5​

Printing numbers from 1 to 5
i = 1

# Repeat as long as i is less than or equal to 5
while i <= 5:
    print(i)
    # Increment i by 1
    i += 1

This code runs print(i) as long as i is less than or equal to 5, then increments i by 1.

The loop will terminate when i is no longer less than or equal to 5 (i.e., when i becomes 6).


What is an Infinite Loop?​

An infinite loop is a loop that never ends because the condition always remains true.

Infinite loops can halt a program or consume excessive resources, causing bugs.

It's crucial to define the condition clearly to avoid infinite loops.


Example of an Infinite Loop​

Example of an Infinite Loop
i = 1

while i <= 5:
    print(i)
    # The value of i never changes, so the condition is always true, causing an infinite loop

In the code above, i never increments, so the condition i <= 5 is always true, resulting in an infinite loop.


Preventing Infinite Loops​

To prevent infinite loops, ensure that the loop includes code that changes the condition from true to false.

For example, you can increment i or adjust the logic so that the condition eventually becomes false.

Example to Prevent Infinite Loop
i = 1

# Loop terminates when i is greater than or equal to 20
while i < 20:
    print(i)
    # Increment i by 1
    i += 1

When Do We Use the while Loop?​

The while loop is useful for performing repetitive tasks until a certain condition is met.


Use Case Example: Repeating Until a Desired Input is Received​

You can use a while loop to continuously receive input from a user until they decide to quit.

Repeat until the user inputs 'q'
user_input = ""

# Repeat until the user inputs 'q'
while user_input != "q":
    user_input = input("Enter 'q' to quit: ")

This code will keep taking input from the user until they enter 'q'.

Once user_input is 'q', the loop terminates, stopping the input process.

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