Yes, it is negative, because you're using signed char data type where the most significant bit is used as sign bit (-127..127). Use unsigned char for range 0..255.
I think that the IDE saves files by default in UTF-8 encoding, but it also might use system's default encoding. In Linux you can check what's the default from LANG or LC_ALL env. variables, I don't know how to check that in Windows or OS X.