Indicates if a character is a hexadecimal digit (0 to 9, A to F,
    or a to f) in the program's current locale.

    Format

      #include  <ctype.h>

      int isxdigit  (int character);

1 - Argument

 character

    An object of type int. The value of character must be
    representable as an unsigned char in the current locale, or must
    equal the value of the macro EOF. If it has any other value, the
    behavior is undefined.

2 - Return Values

    nonzero            If a hexadecimal digit.
    0                  If not a hexadecimal digit.