Chapter Review Questions#

Note

Source: Adapted from the C# edition (while/reviewwhile.rst). Python-specific questions on input() validation and break/continue are original additions.

When should you prefer a while loop over a for loop?
What is an infinite loop?
1. Give an example of code that produces one.
2. How do you stop an infinite loop that is running in a terminal?
What is a sentinel value in a while loop?
1. Define the term.
2. Write a short loop that reads integers from the user until the user enters 0, then prints the sum.
Consider this loop:
```
n = 10
while n > 0:
    print(n)
    n -= 3
```
1. What does it print?
2. Does it terminate? Explain why.
What does break do inside a while loop?
What does continue do inside a while loop? How is it different from break?
Write a while loop that prints the powers of 2 (1, 2, 4, 8, …) that are less than 1000.
Input validation.
1. Write a loop that repeatedly asks the user to enter a positive integer and keeps asking until they do.
2. Why is a while loop more appropriate than a for loop for this task?

Trace the following code by hand and predict the output:

i = 1
total = 0
while i <= 5:
    total += i
    i += 1
print(total)

What is the difference between a pre-condition loop (while condition at the top) and checking the exit condition inside the loop body with break? Give one situation where the break form is cleaner.