unsigned char x = 0xC2;

printf("this is the problem %02X\n", x);

result is:

this is the problem FFFFFFFC2

This is a compiler issue. You told the compiler that x was of type unsigned char and it ignored you. When x was converted to an argument, the compiler treated it as signed. Once x gets sign extended, there's no way for the printf function to know.

Regards, Charlie