this is an issue within your code, not the kata

two problems here :

• if result is an empty string, its length is 0, so you do result[-1] = '\0', that's an out of bounds write:

  result[strlen(result)-1] = '\0';
  

• pos should have enough space to handle 2 digits + 1 space + 1 nul terminator = 4 chars, but you wrote char pos[3];

Oh, didn't know that about the calloc, thank you for pointing this out!

tnx, i appreciate it.