Interactive `while` Loops

while loops are excellent for scenarios where you don't know how many times the loop needs to run (e.g., waiting for user input or checking network status).

Sentinel Value

A sentinel value is a specific input or condition that signals the termination of the loop.

Example: Simple Calculator Menu

python running = True

while running: user_input = input("Enter a number to square or 'quit' to exit: ").lower()

if user_input == 'quit':
    running = False # Sentinel condition met
    print("Exiting calculator.")
    
elif user_input.isdigit():
    num = int(user_input)
    print(f"The square of {num} is {num ** 2}")
    
else:
    print("Invalid input. Try again.")

Infinite Loops

A loop where the condition never becomes False is an infinite loop. This usually freezes your program.

python

DANGER: Infinite loop example

while True:

print("Help! I'm trapped!")

Always ensure that inside your while loop, something changes that affects the control condition.

Interactive while Loops