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Iterating Backwards in C

27 points cremno 3 days ago 12 comments

abstractspoon 2 days ago | parent

I've been using this method for more than 30 years!

MaulingMonkey 1 hour ago | parent

I prefer:

    const size_t n = 10;
    for (size_t i = n; i --> 0;) {
        std::cout << i << "\n";
    }

ranger_danger 1 hour ago | parent

Cute but wouldn't work with ssize_t :)

VHDL's array/vector syntax actually works a similar way:

-- gives 0, 1, 2, 3:

for i in 0 to 3 loop

-- gives 3, 2, 1, 0:

for i in 3 downto 0 loop

-- Source - https://stackoverflow.com/a/7642026 -- Posted by Kerrek SB -- Retrieved 2026-10-29, License - CC BY-SA 3.0

fourthark 34 minutes ago | parent

Does work with ssize_t, just not necessary.

ranger_danger 5 minutes ago | parent

Depends on your definition of "work".

For me it does not work because I'd want to use it with values < 0, but the for loop checks for > 0, so I would have to modify that first.

hedgehog 1 hour ago | parent

That's a certain kind of taste... I checked out your home page, game dev, check, and this work of art is worth linking (no irony, I love it):

http://maulingmonkey.com/brainfuck/

omoikane 3 minutes ago | parent

That looks like the brainfuck mandelbrot set by Erik Bosman, but the example is missing the header line with the credit. The one I saw came from here:

https://github.com/thaliaarchi/bfcorpus/blob/main/ebosman/ma...

Be sure to check out other files in that directory for how the program is assembled.

(Erik Bosman's mandelbrot set is a personal favorite of mine, very useful for benchmarking brainfuck interpreters)

kenferry 53 minutes ago | parent

I know it's "too clever", but if I'm writing code no one else will ever see,

  while (i --> 0) {
      // use array[i]
  }
easy to read (if not understand), and correct!

stephencanon 51 minutes ago | parent

Always.

(Hi Ken!)

krackers 46 minutes ago | parent

Oh I remember this from the classic SO post, but it was just presented as a funny trick. I never realized that it solves the issue mentioned in the article and there is a legitimate use-case for post-decrement in the comparison itself.

https://stackoverflow.com/questions/1642028/what-is-the-oper...

viega 38 minutes ago | parent

I always use unsigned values and do:

  while (i-- != 0) { ... }
It's more clear than the most idiomatic way, which is to drop the explicit comparison:

  while (i--) { ... }
All of it is better than the clunky old for-loop syntax.

mtklein 1 minute ago | parent

I don't think it's too clever at all. Notably it works with both signed and unsigned i. Frankly if I see anyone doing anything other than this, they're wrong.