isHexadecimalCharacter function
Check if a character is hexadecimal
Implementation
bool isHexadecimalCharacter(String character) {
return (character.compareTo('0') >= 0 && character.compareTo('9') <= 0) ||
(character.compareTo('a') >= 0 && character.compareTo('f') <= 0) ||
(character.compareTo('A') >= 0 && character.compareTo('F') <= 0);
}