If you use the C compiler, you don't need to consider this problem at all, because the compiler has solved it for you, and you only need to define the 16 bit variable (such as int type).

However, if you write a program in assembly language, you must allocate memory cells (font variables) for the program, use four or more 8-bit registers, and first use the lower 8 bits and then use the upper 8 bits for operation, but pay attention to the changes of the status registers.