问使用汇编代码执行表达式

EN

TITLE
;--------------------------------------------------------------

.MODEL SMALL
.STACK 64
.DATA

    MSGA    DB 13, 10, "Input expression: ","$$$"               ;asks the user input expression ie. 5+2
    MSGADD  DB 13, 10, "The sum is: ","$"                       
    MSGSUB  DB 13, 10, "The difference is :","$"
    MSGMUL  DB 13, 10, "The product is: " ,"$"
    MSGDIV  DB 13, 10, "The quotient is: ","$" 


    NUM1 db ?
    NUM2 db ?
    OP db ?

    .CODE


    MAIN PROC NEAR


        MOV AX,@DATA 
        MOV DS,AX

        LEA DX,MSGA   
        MOV AH,09H      ;reads the user input
        INT 21H

        MOV AH,01H      ; scan NUM1
        INT 21H         ;interruption
        SUB AH,32
        MOV NUM1,AH


        MOV AH,01H      ; also reads from the keyboard
        INT 21H         ; scan NUM2
        SUB AH,32
        MOV NUM2,AH

        ;MOV NUM2,AL

        MOV AH,01H      ; also reads from the keyboard
        INT 21H         ; scan OP
        SUB AH,32
        MOV OP,AH




        CMP AX,'+'
        je @ADD

        CMP AX,'-'
        ;je @SUB

        CMP AX,'*'
        ;je @MUL

        CMP AX,'/'
        ;je @DIV

            @ADD:

                ADD AH,NUM1 ;add first number
                ADD AH,NUM2
                MOV NUM1,AH
                ADD NUM1,32

                LEA DX,MSGADD
                MOV AH,09h
                INT 21h

                MOV DL,NUM1
                MOV AH,02h
                INT 21h

            @DIV:
            XOR AX,AX ;EXAMPLE ON THE BOARD
            MOV AX,83H
            MOV BL,2H
            DIV BL

        MOV AH,4CH    ;for exiting purpose
        INT 21H

    @endif:

MAIN ENDP
;---------------------------------------------------------------
END MAIN