std::string o;
...
l = o.length();
char out[l];
...
return out;

• out is a local array variable. with return out; you are returning the address of a local variable, which is incorrect. as soon as the function exits the address becomes invalid.
• out is missing 1 byte for the nul-terminator

the C translation does not describe how the returned pointer should be allocated.

fixed there

(author is gone)

escalated here as an issue

duplicate of this suggestion

Somebody below mentioned that this kata has to be 6 kyu.. I don't think so... (I have not solved it yet...)

Enabled in this fork

Duplicate of this

You misunderstood the behaviour of wrapping (which is, arguably, not described precisely). It is not that when going from positive to negative you always end up with 255. You need to wrap through 255 to lower values, if necessary, so -1 becomes 255, -2 becomes 254, and -12 becomes 244.

L Q Q c U B N
0 -> 2 -> 4 -> 16 -> (copy = 16) -> 4 -> -12 (=255) -> output 255
expected:<2[44]> but was:<2[55]>
Where did I make a mistake?

Haskell translation

I've made an attempt at generating random valid inputs. Loops aren't generated due to the complexity of ensuring that they don't loop forever. However, they should serve the purpose of weeding out any hard-coded solutions.

python new test framework + random tests are required. updated in this fork

Quite funny kata.

Added in latest fork

python new test framework is required. updated in this fork