why adding #define contsants for initializing a const is breaking rule 10.3 ?

[GerlindeKettl]

According to C99, a decimal constant with suffix U is of type unsigned int. (CONST1 + CONST2) is then an expression of type unsigned int. If unsigned int has a size of 32 bit in your environment, an expression with a size of 32 bit is assigned to a variable of type uint16_t which is a narrower essential type.