Exercise 1: Detaching and Reattaching a Running Loop — Possible Solution
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Commands:

  screen -S counter                          # start a named session
  while true; do date; sleep 5; done         # inside the session

  (press Ctrl-a, then d)                     # detach
  [detached from 12345.counter]              # screen's message

  # wait about a minute, then:
  screen -r counter                          # reattach

After reattaching, the window shows a date line roughly every five
seconds, including the lines printed while you were detached. The loop
never stopped.

To finish cleanly:

  (press Ctrl-c)                             # stop the loop
  exit                                       # close the shell

  [screen is terminating]

Because the shell was the session's only window, closing it ends the
session.

WHY THIS WORKS AS AN ANSWER
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The timestamps that appear while you were away are direct proof the
job kept running during the detach. It also shows the difference
between detaching (Ctrl-a d, keeps running) and exiting (ends the
session).