Why are the lists in the test outputs not reversed ordered?

i resolved the ambiguity by adding the following comment in the C initial code:

// it is guaranteed that s1 and s2 have room for
// 1 + max(strlen(s1), strlen(s2)) bytes

added to the description

fixed there

tricky, but not very enjoyable

Nice!

(c-version)

there is a typo in the provided test: The output message labels both expected strings as "S2" - should be labeled as "S1" and "S2".

You're not doing it in-place.

what is this error:
expected [ '7', '6', '5', '4', '3', '2', '1' ] to deeply equal [ 'c', 'b', 'a' ]
my code wotks in browser console though...

nothing, obviously.

Instructions are insufficient and tests don't provide any feedback information.

what should be return from function

This is a very tricky kata. You could have blame the author with such tricky problem, but just do what your mind says then viola it will work!
then you will realize the logic the sensei wants you to know.

clue: the function is void, the length is different and the sensei is clever.

I dont understand , this is my output on my computer:

s1:c b a
s2:7 6 5 4 3 2 1

but tests show:

[Actual]
S1: [1234567]
S2: [abc]
[Expected]
S2: [cba]
S2: [7654321]
[Input]
S1: [1234567]
S2: [abc]

please explain what happens ?

i dont understand what you need me to do after exchanging the values
what should i return with