I question the need of rule 10.6

[jbezem]

I beg to differ. If you use

Code:

#define C_DECIMAL     32768U
#define C_HEXADECIMAL 0x8000U

both constants will be considered to be of type 'unsigned int', the invert operation will invert 16 bit, the cast to 'long' will sign-extend the values to 0x00007FFFUL.
OK, it now depends on what you wanted in the first place, but at least both values are handled identically, and arguably "do what the programmer intended".
IMHO this is much better than without the suffixes.
It would be nice if a compiler could/would warn about a situation like the use of 0x00008000 being used as a constant. By supplying the leading zeroes the programmer at least suggests that she/he intends to provide 32 bits of value. However, the compiler will still create a 16-bit unsigned integer. Here's where tools like PC Lint fill in the gap, if you let them.

FWIW,

Johan