c + c++ = ?

C + C++=?

Different Answers for the Question c + c++=?

Answer1:

c + c++ = 2c
c + c++ = 2c+2

Answer2:

undefined behaviour

Answer3:

how can it give undefined behavior
lets give any value to c
suppose
Int c=1
then 
c + c++ = 2
This is not an undefined behavior.

Answer4:

I think,
the ans is 2c where c =....(means any positive number)

Now Tell Me Which Answer is Correct????