.MODEL SMALL
 .STACK 100H

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

 .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

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

     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

     MOV BH, AL                   ; save Second digit in BH in ASCII Code.
     SUB BH, 30H

     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

     SUB BL, BH                   ; subtract First and Second digit
     
     ADD BL, 30H                  ; convert ASCII to DECIMAL code

     MOV AH, 2                    ; display the character\digit
     MOV DL, BL     
     INT 21H
                         
     MOV AH, 4CH                  ; return control to DOS
     INT 21H
   MAIN ENDP
 END MAIN

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