For characters 0 to 127, you follow the ASCII character set.
As you can see the character after (90) Z
is (91) [
and the character after (45) -
is (46) .
Try
char ch = '-';
ch += '-'; // == (char) 90 or 'Z'
or even more bizarre
char ch = '0';
ch *= 1.15; // == (char) 48 * 1.15 = 54 or '6'