Update question 29

[knatten]

Thanks for helping!

Thank you for helping to port this question from C++17 to C++23.

You'll find the source code in question.cpp, this should normally not need modification.

In C++17, the correct answer is:

The program is guaranteed to output: 121

Please verify that this is still correct in C++23. If it is, please do the following:

• Update explanation.md:
  • Refer to the correct section numbers
  • Use updated quotes from those sections (the wording might have changed)
  • Make sure the rest of the text in the explanation is consistent with the new standard
• Update hint.md if needed (usually not needed)

Note that some older questions are missing references to the standard, we don't need to fix that now.

If you get stuck, please describe the problem in detail in a comment to the issue, and a maintainer will add the help wanted tag so others can chime in.

If the correct answer has changed from C++17 to C++23, you can either just leave a comment in this issue, or see the instructions for updating meta data.

[knatten]

No update needed