C code to parse out certain characters in a string
outputString doesn't have enough room to accomodate the results. It can hold just one byte. It is just unlucky coincidence that the code does not segfault. In any case, undefined behaviour.

If the intention is just to print the result out, you don't need outputString at all. Just printf the tokens as you compute them.
strcat must scan the entire outputString to figure out where it ends. The overall time complexity of the repeated strcats becomes roughly quadratic. I recommend to maintain a pointer to the end of outputString, and strcpy the token.