Interval Comparisons

Would it break backward compatibility for C to add a feature like this
from Python? Namely, the ability to check if a value lies in an interval:

    def valid_char(c) :
        "is integer c the code for a valid Unicode character." \
        " This excludes surrogates."
        return \
            (
                0 <= c <= 0x10FFFF
            and
                not (0xD800 <= c < 0xE000)
            )
    #end valid_char