2025 – The 29th IOCCC

Where to start

See below for links to the 2025 winning IOCCC entries.

Check out the index.html web pages for each winning entry. They have
most of the information you need to compile and run the winning program.
Take a look at the winning source code and try to figure out how it works.
You might also want to check out the author’s remarks for even more details.

You may download all winning entries in the form
of a compressed tarball for this year’s contest.

For IOCCC29, the volume and quality of submissions were at near-historic heights.

IOCCC28 was speculated to have attracted a record number of submissions
due to the 4-year absence, allowing authors to refine their submissions,
resulting in a higher-than-usual submission quality.

IOCCC29 was the second consecutive contest after the 2020-2024 hiatus.
And yet, the number of submissions for IOCCC29 was similar to last
year’s contest, and the overall submission quality remained high for
this contest. So perhaps the increased submission volume, combined
with a higher-than-usual submission quality, is due to factors such
as improved website design, increased social media presence, authors
building on the ideas of past winning entries, and other factors?

Starting with the close of IOCCC28, the procedures used for
closing the contest to new submissions, the judging process,
selecting the winning entries, preparing the update to the website,
and the process to create the live show on the
Our Favorite Universe
were carefully documented. And while this documentation required
additional time as well as more effort, the documentation process
resulted in overall improvements to how the IOCCC is run.

A few days after the presentation of the winning entries for IOCCC29 has been made
on the Our Favorite Universe
YouTube channel. The recording of the main show will be divided up into individual segments.
Then, each winning entry will be updated to include a link to a YouTube
segment under a new Award presentation near the top of the winning
entry’s index.html page.

Fun challenge info

We have added fun challenges to this year’s winning entries
competition, under the “Judges’ remarks” section. After you figure
out what a given winning entry does, we encourage you to attempt the
fun challenge.

Some of these challenges are easier than others. In some cases, you’re
asked to create an alternative version of prog.c or a related file.
In some cases you are asked to produce an explanation about something.

If the fun challenge is still open (check the “A fun challenge”
section for the given winning entry), consider submitting a
GitHub pull request as a contribution.

If the fun challenge is closed, but you think you have a better solution,
consider submitting a GitHub pull request as a contribution.
If the IOCCC Judges agree that you solution is better, we will consider it.

If you believe you have an even better (or improvement) to winning entry’s fun challenge,
please consider submitting a GitHub pull request,
for the IOCCC judges to consider.

Rules and Guidelines for this contest

The final versions of the IOCCC rules and guidelines that were in effect for this contest were:

The IOCCC rules and guidelines for IOCCC29 represented a substantial
rewrite over previous contests, thanks in part to a number of volunteers:
giving the IOCCC judges useful edits, text rewrites, consolidation,
as well as overall improved organization.

Looking forward to the next contest

We plan to open IOCCC30 towards the end of 2026 and have the contest run
for a similar amount of time, closing sometime towards the end of Q1 2027.

As we perform the actions needed to open IOCCC30, we plan to internally
document the process as we did during the closing of IOCCC29.

While working on creating potential write-ups for submissions that entered
the final round of the set of judging rounds:

• A few submissions were set aside in the final round of the final set of rounds.
• We gained an additional level of appreciation for a number of the remaining entries.

While the winning entry authors came from
locations of previous winning authors,
this IOCCC29 had an author – jingp49
from a new location: Taiwan.

This contest saw a Hat trick
of Hat-tricks by:

Notable and remarkable winning entries of IOCCC29 include, but are not limited to:

Those are just a few of the many amazing winners of the IOCCC29, so be sure to check out the rest!

As we discussed above, there were quite a few excellent submissions that
didn’t quite make the final cut. We truly appreciate the hard work
each author put into their entries, but we’re sorry that we can’t
award based solely on effort.

We received many great submissions that didn’t quite make the cut
as winners. If you submitted something for IOCCC29 that didn’t
win, think about polishing your code and giving it another shot for
IOCCC30. Interestingly, more than one winner of IOCCC29 was
actually an improved version of code that didn’t win in a previous
contest.

Encouragement for those who did not win this year

We know many of you that submitted to the IOCCC put in a ton of effort
into your submissions for this year’s IOCCC. We can’t just give out
awards to everyone. That would mean taking away from the submissions
that we think are the best and deserve to win.

Sometimes, a final round submission might be good enough to be a
winning IOCCC entry, only to be beaten by a similar, but slightly better
submission. If you think this happened with your submission, consider
submitting an enhanced version to the next IOCCC.

PLEASE DO NOT give up hope! There are some submissions that have been
submitted with revisions, multiple times before rising to the level of
a winning IOCCC entry. You might also want to try with a different type
of submission altogether for the next IOCCC.

If you’re not planning to improve and resubmit your non-winning entry
for the next IOCCC, you’re welcome to publish it.

On compiling and running winning entries

Some C compilers aren’t as great as they could be. If yours isn’t
working well, you might want to try compiling with an updated version
of clang and/or gcc instead.

If you encounter problems in compiling and/or running the winning entries, see the FAQ on:

For additional information on how to submit fixes, see the FAQ on:

For even more information

Download all winning entries from 2025

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