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[Bak]

found these online, thought they were fun so I'll share. no cheating! I'll do one at a time; there's 5 total.

challenge #1: write strlen function without any types in the function body (types such as 'int' or 'char' or 'char*')

here's standard version for reference:

Code: Show/Hide int strlen(char* s) {   int len = 0;   for (int x = 0; s[x]; ++x)     ++len;   return len; }

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[Dr Brain]

Took me a few minutes of trying to figure out how to get an extra hidden parameter into the declaration, but recursion is the answer.

Code: Show/Hide int strlen(char *s) {    if (*s) return strlen(s+1) + 1;    else return 0; }

Note: I didn't compile or test it, but it gets the general idea across.
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[Bak]

That's right. Next one is a little easier, but try to do it without cheating (if you cheat don't post answer).

Challenge #2: what's the following code output and why:

Code: Show/Hide printf("%c", 1["dr brain"]+1);

[Dr Brain]

s

The brackets don't care about order, so 1["dr brain"] is the same as "dr brain"[1], so that whole expression is 'r'+1 or 's'.

[Bak]

Challenge #3: Write a program that only prints "dr brain won #2" and has exit code 100 when the process terminates. Don't use any semicolons.

[Doc Flabby]

pretty sure this isnt the right way to solve this one

Code: Show/Hide int main() {    return printf("dr brain won #2 \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b \b\n") }

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[Samapico]

That doesn't compile... return requires a ;

in VS anyway
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[Samapico]

I'd do something like


if ( exit( printf("dr brain won #2")+85 ) )
{
}

But exit returns a void, so it doesn't compile either

[Dr Brain]

Took a lot of head banging to come up with this:

Code: Show/Hide int main() {     if (!pthread_create(malloc(sizeof(pthread_t)), NULL, exit, printf("dr brain won #2\n") + 100 - 16)) {while(1){}} }

I'd wager there's a better solution than this.

[Samapico]

+ 100 - 16 ? lol

[Dr Brain]

I had to add a \n at the end because zsh freaks out if it's missing, so it was 16 instead of 15.

[Samapico]

...

My point was, + 84 would be simpler
Though I can see the why... but still

[Hakaku]

[Dr Brain]

Yes, the comma operator was the missing piece of the puzzle. I'd completely forgotten that it existed. Kudos for a more elegant solution.

[Initrd.gz]

Cuz just maybe we don't want to use semicolons in C

[Bak]

yeah comma operator was the trick, although pthread version was pretty original, i'll post next one in a little bit

if (printf("dr brain won #2"), exit(100), 0) {}

[Bak]

Challenge #4: What's the following code print and why:

Code: Show/Hide #include <stdio.h> int i(int i, int ii) {    return ii == i; } int main() {    int (*ii)(int, int) = i;    int i = 0;    if (i++ == ++i)       printf("%i", i + 1);    else       printf("%i", i);    if (ii(i++, ++i))       printf("%i", i + 1);    else       printf("%i", i);    if (ii(++i, i))       printf("%i", i + 1);    else       printf("%i", i);    return 0; }

[Samapico]

Never seen that comma operator... well... except in a for statement...

So basically, the value returned by the whole expression is the result of the part after the last comma?


And holy shit, that's a lot of i's

[Samapico]

hmm... ii would be a pointer to the function...

i++ == ++i
would be false, and increments i twice...

> 2

you call ii with (2, 3), which returns false, i becomes 4

> 4

you call ii with ... I guess it depends in which order arguments are evaluated. ......... hmmmmm hold on a second. I think they're evaluated in reverse order... which means my past reasoning doesn't work.


The first if block is fine...
>2
the next one...
i = 2
second argument evaluated first, gives 3, then first argument, gives 3 also; i becomes 4 after
so... it returns true
> 5

now i = 4
you call ii with (5, 4) -> false
> 5

So...
output:
> 255

[Bak]

[Samapico]

So did I get it or not?

[Bak]

Yes, you could also compile and check

Anyways, Challenge #5 (last one):

Here is a swap function:

Code: Show/Hide void swap(int* a, int* b) {    int temp = *a;    *a = *b;    *b = temp; }

Now rewrite the body of the function to have the same functionality but only using one semicolon, no commas, and not containing "if" anywhere in the body.

[JoWie]

Code: Show/Hide void swap(int* a, int* b) {    *a ^= (*b ^= (*a ^= *b)); }

assuming a != b



or (safe but lame version)

Code: Show/Hide void swap(int* a, int* b) {    #define lol ;    int temp = *a lol    *a = *b lol    *b = temp lol }

[Bak]

can you do it without assuming a != b?

lol@lame version too

[Doc Flabby]

Code: Show/Hide void swap(int* a, int* b) {        a==b ?   b = a :  *a ^= (*b ^= (*a ^= *b)); }

^^