Thats C grammer to represent the Hex numbers. Assemblers may not support that kind of notation.


here problem is the number has not been represented according to the grammer and creating ambiguity(see what Jan wek said below). here is an example

C0: DS 1            ;define a varible named C0


mov R0,#C0          ;load R0 with the address of C0        
mov A,@R0           ;self explanatory



and


mov R0,#C0          ;load R0 with a constant

how will compiler know that #C0 is an variable or a constant. the compiler differentiate them like Jan already stated.



Abhishek