sum-vars.asm

 TITLE sum-vars : An AL Program to read two digits whose sum is less than 0,
              ; computes and display their sum (using variables).

 .MODEL SMALL
 .STACK 100H

 .DATA
    PROMPT_1  DB  'Enter the First digit : $'
    PROMPT_2  DB  'Enter the Second digit : $'
    PROMPT_3  DB  'Sum of First and Second digit : $'

    VALUE_1   DB  ?
    VALUE_2   DB  ?

 .CODE
   MAIN PROC
     MOV AX, @DATA                ; initialize DS
     MOV DS, AX

     LEA DX, PROMPT_1             ; load and display the PROMPT_1
     MOV AH, 9
     INT 21H

     MOV AH, 1                    ; read a character
     INT 21H

     SUB AL, 30H                  ; save First digit in VALUE_1 in ASCII code
     MOV VALUE_1,AL

     MOV AH, 2                    ; carriage return
     MOV DL, 0DH
     INT 21H
                         
     MOV DL, 0AH                  ; line feed
     INT 21H

     LEA DX, PROMPT_2             ; load and display the PROMPT_2
     MOV AH, 9
     INT 21H

     MOV AH, 1                    ; read a character
     INT 21H

     SUB AL, 30H                  ; save Second digit in VALUE_2 in ASCII code
     MOV VALUE_2,AL

     MOV AH, 2                    ; carriage return
     MOV DL, 0DH
     INT 21H
                         
     MOV DL, 0AH                  ; line feed
     INT 21H

     LEA DX, PROMPT_3             ; load and display the PROMPT_3
     MOV AH, 9
     INT 21H

     MOV AL, VALUE_1              ; add First and Second digit
     ADD AL, VALUE_2

     ADD AL, 30H                  ; convert ASCII to DECIMAL code
     
     MOV AH, 2                    ; display the character
     MOV DL, AL     
     INT 21H
                         
     MOV AH, 4CH                  ; return control to DOS
     INT 21H
   MAIN ENDP
 END MAIN