String containing degree symbol

I suppose that this is really a GNU C question, but I’m guessing that someone might have solved the problem.

my display uses a value of 0xB0 for the ° symbol.

if it try to put it in a string as a char I get a warning that it has changed the value from 176 to -80. 

if I make the string into an array of unsigned char then it won’t allow text in it.

Obviously -80 is still 0xB0, so I should still get ° displayed, but how do I avoid being chastised by the compiler?