Check your understanding of the previous reading: how many times a while loop runs, and the while loop patterns.

Question 1

How many times does the loop body below execute?

command = ""
words = []
while command != "quit":
    command = input("Type a word:")
    words.append(command)
print(words)

Select one answer, then check.

None
Not quite. command starts as "", which is not "quit", so the condition is true the first time and the body runs.
At least once
Correct. command starts as "", so the body runs at least once; after that, it depends on what the user types, and the loop stops once they type quit.
At least twice
Not quite. If the user types quit the first time, the condition is false after one pass, so the body runs only once.
No more than 10 times
Not quite. Nothing in the loop counts the passes: it keeps going for as long as the user types something other than quit.

Question 2

How many times will the code below print? If the loop executes infinitely, then enter -1 instead.

counter = 500
while counter > 1:
    counter = counter - 2
    print(counter)

Show worked solution

counter goes 500, 498, …, 2, 0, and every pass prints the new value: the even numbers from 498 down to 0. That is 498 / 2 + 1 = 250 prints. After printing 0, counter > 1 is false and the loop ends.

Question 3

How many times will the code below print? If the loop executes infinitely, then enter -1 instead.

counter = 500
while counter > 1:
    counter = counter // 2
    print(counter)

Show worked solution

counter // 2 halves the value and rounds down: 250, 125, 62, 31, 15, 7, 3, 1. That is 8 prints; once counter is 1, counter > 1 is false and the loop ends.

Question 4

Match each description to the appropriate pattern.

#	Description	Pattern
1	An infinite loop used to make a program continue indefinitely.
2	Satisfying some complicated constraint by trying many different numbers over and over again.
3	Iterating over numbers, usually in a non-linear fashion.
4	Repeatedly getting text from the user in order until the input is correct.
5	Repeatedly getting text from the user in order to execute commands based on what they enter.