Working with 3 byte numbers

[Bruce]

You don't even need to mess with assembler. Here's a really simple example,
and it's all in BASIC;

  A VAR WORD
  B VAR WORD
  X VAR BYTE
  NumToAdd VAR BYTE
  NumToAdd = $2E
    
MAIN:
    A = $0001
    B = $FFFE
    FOR X = 1 TO NumToAdd
      B = B + 1
      IF B = 0 THEN A = A + 1
    NEXT X

You can extend this to pretty much any size variable you need.