Transfrom the Expression - Workin C code, gives wrong answer on Chef

my code:

it works for the given test cases, it works for (a+©), it works for test cases of decreasing length.
i’ve tried it both with and without a null terminated line, and it still gives WA on submission.

I just need a hint as to why. i’ve yet to find a case that it should fail, but apparently it does.

try this case (a+b)*(c-d)