I haven't taken on this kata yet, but I already want to say that yes, this is a greate classic task, thanks!

the level for this kata is too high. if the task involved creating a queue class on its own, then it would be 4kyu, otherwise it would be 6kyu.

Because you're doing something that is quite wrong. One may then debate to what degree you should be shown the problem and to what degree you should go figure it out. Since it's something that is happening in your own function you ought to be able to figure it out with printf. Depending on how and what you print it may be tricky to figure out the exact cause but you'll at least be able to figure out where it happens which gives you a very limited amount of code to focus your debugging on. But that's C for you isn't it? Requiring you to navigate that. You've also got the test code here

don't know why it gives an error on random tests:
code below

thanks for the thorough answer!

• char* res=calloc(strlen(s),1);
  

  this does not account for the nul terminator (1 byte is missing)

• char* res=(char*)malloc(strlen(od));
  

  same remark

• if(*s=='\0'){
    return "";
  

the tests expect the returned string to be free()-able. "" is a string literal that cannot be freed

• if(*od=='\0'){
    char* cp=NULL;
    strcpy(cp,s);
  

you are attempting to write at the null pointer here. this will crash. you have to allocate memory for `cp`.



your code passes once all these are fixed.

to easy for 6 kyu

the word "java" is not similar to "heaven".

dealing with decimals here and in similar katas feels like a pain in the ass

this is the base

A really good solution!

The famous C++'s "Unsafe memory" ))

wtf ???

are you kidding me or what?