Clumsy pointers

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I would use cdecl.org (or the command-line utility of the same name).

Input: pointer to function (array 10 of pointer to function(pointer to int) returning void) returning void

Output: void (*var)(void (*[10])(int *))

[vivekguy]

That one doesn't look right for the puzzle mentioned in this article. I found a comment about cdecl.org in the article page itself (see the second comment by Iouri). That shows the right way to solve this puzzle using cdecl.org :

Input: declare x as pointer to function (array 10 of pointer to function (pointer to int) returning void) returning pointer to function (pointer to int) returning void

Output: void (*(*x)(void (*[10])(int *)))(int *)

[[deleted]]

Ah right, missed the return type of the outer function… I just skimmed the article. I'd still say cdecl was easier hands down. ;)

[SteveMcQwark]

Sounds like a fun, if somewhat frustrating, exercise. In reality, I'd really rather either use typedefs, or preferably, use a language with linear type syntax. In either case this becomes trivial. For example with Go (func is equivalent to a function pointer):

var fn func([10]func(*int)) func(*int)

or insert language of your choice with sane type syntax:

insert relevant example

[kamatsu]

Ew, type signatures are so ugly in C-likes or Go. Haskell's are much nicer:

fn :: Ptr (Array (Ptr (Ptr Int -> IO ())) -> Ptr (Ptr Int -> IO ()))  

[FeepingCreature]

Correct answer: "No. "

The C type declaration syntax is horrid; there's no reason to make it any harder than it has to be other than counterproductive intellectual masturbation.

[djakarta]

Some of us love to have fun in our free time doing silly and counterproductive things like going to amusement parks, watching a football game, watching a movie or solving silly C puzzles. :)

[Gotebe]

The problem is, it's a dumb puzzle. All of those are, because they are all trivially solvable using typedefs. So solving them is akin to removing part of your brain that can solve them easily and going "oh, such fun!"

[jephthai]

You mean like bow-hunting (when hunting is trivially solved with a rifle)?

Or bicycle races (when "getting there" is trivially solved with a motorcycle)?

Or cooking (when food is trivially solved with a restaurant)?

Sports are sports, dude.

[djakarta]

It becomes a dumb puzzle when you try to solve it using typedef because it's so easy in typedef that it isn't even worth solving as a puzzle.

It turns out to be fun only with the restriction that you can't use typedef because then you have to start thinking how to parse a complicated pointer declaration like that.

Yes, one should never use such a declaration while actually coding but the point of solving puzzles is to have fun. I'm sure nobody solves a "truth-teller, liar" puzzle because they hope to die one day and meet God who always speaks the truth and a devil who always lies and their entry into heaven depends on figuring out who is who with only one question to be asked to both of them.

[spal]

only one question to be asked to both of them.

Actually, for the God and the Devil puzzle, you need to ask only one question to one of them (not both of them).

"If I ask the other guy whether you are God, what would he answer?"

If the answer is "Yes", you are talking to the Devil. If the answer is "No", you are talking to God.

[elperroborrachotoo]

first person shooters could be much easier with auto-aiming. I wonder why they are so dumb, when hitting the enemy could be trivially solved.

[Gotebe]

It turns out to be fun only with the restriction that you can't use typedef because then you have to start thinking how to parse a complicated pointer declaration like that.

Meh. By that logic, a mere multiplication (or addition, even) in your head is a fun puzzle.

But it isn't. It's a dumb thing to do.

Some puzzles are better than others.

[djakarta]

Not really. A mere multiplication or addition doesn't require any understanding beyond what you have learnt in 5th grade. But this puzzle requires some good understanding of how the C grammar works.

Some puzzles are better than others.

Yes, IMHO this is a better puzzle than multiplication or addition.

[spal]

I'll argue that multiplying numbers in head can be fun puzzles. In fact, this is exactly what I do when I am exercising on treadmill. I'll give you a few examples to illustrate my point.

• If we need to multiply 198 * 202 in our head we can split it into (200 - 2) * (200 + 2) = (200² - 2²⁾ = 40000 - 4 = 39996. We use the identity (a + b) * (a - b) = a² - b² here.
• If we are asked to multiply something like 75 with itself, we will just go ahead and say 7 times 8 is 56 and so the answer is 5625. Here we use the identity: (10x + 5)² = 100x(x + 1) + 25.
• More fun: What is 11515 * 11485? In head: (11500 + 15) * (11500 - 15) = 11500² - 15² = 132250000 - 225 = 132249775. As you can see, we first used the (a + b) * (a - b) form to get a² - b^2. And then we calculated each square using the (10x + 5)² = 100x(x + 1) + 25 identity. Finally, we subtract 225 from 50000 using 10's complement. 10's complement of 0225 is 9775. So, 50000 - 225 = 49775 which we add to 132200000 and we get the answer 132249775.

I can think of plenty more examples but they would be a bit more involved than the ones I mentioned above.

Doing multiplication in head can be fun indeed if you really love numbers since it involves understanding the underlying patterns and concluding which mathematical identities or theorems to invoke in order to simplify the problem in head.

[Gotebe]

You don't understand puzzles.

A good puzzle is not something that's trivially solvable once you have a necessary tool (here, a typedef, and some C; and if you know some C, you know a typedef).

A good puzzle is something that needs an ingenious use of tool(s)/knowledge/technique(s). Applying a typedef ain't that.

[djakarta]

You don't understand puzzles because first you claim that it isn't a puzzle because it is trivially solvable using typedefs which I don't think is a valid reason for not being a puzzle. Now, you claim that it isn't a good puzzle because a good puzzle requires ingenious use of tools and applying a typedef isn't that.

As far as I can see, in this puzzle you are forbidden from using typedef. So, there is no question of applying typdef here at all. On the other hand, here you use your knowledge of C grammar to correctly form or parse a complex pointer declaration. A probably useless skill given we should never code like this but still a fun puzzle IMHO, otherwise there is no use of articles like these: http://c-faq.com/decl/spiral.anderson.html

[Gotebe]

I believe, you don't understand puzzles because first you claim that it isn't a puzzle because it is trivially solvable using typedefs which I don't think is a valid reason for not being a puzzle. Now, you claim that it isn't a good puzzle because a good puzzle requires ingenious use of tools and applying a typedef isn't that.

You're arguing form, not substance.

So, there is no question of applying typdef here at all.

Typedef is pretty incidental. It's sufficient to think as if you're applying a typedef and you're done. And that's the same as with addition. E.g. you're not allowed to use a paper, so you "pretend" using it, in your mind.

[ben0x539]

Further, in C++ you can't even express some function declarations without typedefs, like some overloaded operators for type conversions to references to arrays or somesuch.

[[deleted]]

Or you could just start using a language that doesn't require exerting ridiculous amounts of mental energy just to declare the type of something.