DECODEIT giving WA

I tried a solution for DECODEIT in which i used bit manipulation in such a way that 0000 ->a 1000->b, in short, I took ith bit and set it in a number at ith bit on a number… and the character form of number hence obtained+‘a’ gives the character we want, But for this solution I am getting a WA response, What case have i missed in this case?? Can u plz help me out???
HERE IS MY SOLUTION