jmp start
;****************************
;* Program to read in two   *
;* numbers and add them     *
;* and print out the result *
;****************************
  number db 7 dup 0         ; string which will store input and output
  n1     dw 0               ; two input variables
  n2     dw 0
  res    dw 0               ; one output variable
  cr     dw 13,10,"$"       ; carriage return, line feed
start:
  mov dx,offset number
  mov bx,dx
  mov b[bx],5           ; maximum 5 characters to read
  mov ah,0ah
  int 21h           ; read in a string from keyboard
  mov bx,offset number +1
  mov cx,00
  mov cl,[bx]           ; cl now contains number of digits
  mov ax,00         ; ax will contain the number input
  usedigit:
    inc bx          ; get next digit
    shl ax,1            ; multiply by 10 using 2 shift ops and an add...
    mov dx,ax           ; ... x*8 + x*2 = x*10 is the principle.
    shl ax,2
    add ax,dx           ; ax is now multiplied by 10
    mov dx,00
    mov dl,[bx]         ; dl has new character
    sub dx,48           ; subtract 48 = ascii('0') to get number value
    add ax,dx           ; add to ax
  loop usedigit         ; loop statement= jmp if cx > 0
  cmp n1,00         ; see if this is first or second number read
  jnz second
  mov n1,ax         ; assign it to the first variable
  jmp start         ; read in another number
second:
  mov n2,ax         ; or assign to second variable and continue
print_cr:
  mov ah,09
  mov dx,offset cr      ; print out a carriage return character
  int 21h
addnos:
  mov ax,n1         ; move numbers to registers ...
  mov bx,n2
  add ax,bx         ; ...and add
  mov res,ax            ; store the result
  mov cx,00
setup_string:
  mov bx,offset number+7    ; put a $ at end of buffer.
  mov b[bx],'$'         ; we will fill buffer from back forwards
  dec bx
  mov ax,res
convert_decimal:
  mov dx,10
  div dl            ; divide by 10
  add ah,48         ; convert remainder to character
  mov [bx],ah           ; and move to buffer for output
  dec bx
  mov ah,00         ; quotient becomes new value
  cmp ax,00         ; if we haven't got all digits divide again
  jnz convert_decimal
printout:
  mov dx,bx
  inc dx            ; we decremented once too many, go forward one.
  mov ah,09
  int 21h           ; output the string
close:
  mov ah,4ch
  mov al,00
  int 21h           ; end program