Assembly 8086 assignment work calculator

; multi-segment executable file template.

data segment
    menu db "Please enter your Choice",0ah,0dh,"Add ->'+'",0ah,0dh,"Sub ->'-'",0ah,0dh,"Mul ->'*'",0ah,0dh,"div ->'/'",0ah,0dh,"Mod ->'%'",0ah,0dh,"Pow ->'^'",0ah,0dh,"Exit ->'x'",0ah,0dh,"$"
    menuLength dw menuLength - menu

    userSellection db ?

    tempNum db 3 dup (?)
    tempNumLength dw tempNumLength - tempNum

    firstNumMSG db 0ah,0dh,"Please enter the First Number: $"
    firstNumMSGLen dw firstNumMSGlen - firstNumMSG

    secendNumMSG db 0ah,0dh,"Please enter the Secend Number: $"
    secendNumMSGLen dw firstNumMSGlen - firstNumMSG

    resultMsg db 0ah,0dh,"Result: $"
    resultMsgLen dw resultMsgLen - resultMsg

    firstNum db ?
    secendNum db ?
    result db ?

ends

stack segment
    dw   128  dup(0)
ends

code segment
start:

    mov ax, data
    mov ds, ax
    mov es, ax

restartCalc:
mov result, 0
mov userSellection, 0
mov firstNum, 0
mov secendNum, 0
    ; print menu -----
    mov dx, offset (menu)
    mov ah, 9
    int 21h

    ;input from user ----

    mov ah, 1
    int 21h
    mov userSellection, al

    cmp al, 'x' ; end and not get 2 more numbers if option is x
        je end

    ;input for numbers - first num

    mov bp, 2
    mov si, offset(firstNum)

    ;print first request for input
        mov dx, offset (firstNumMSG)
        mov ah, 9
        int 21h

    num2:
    mov bx, 0
    mov cx, tempNumLength ;set cx for max len of number
    dec bp ; flag for current number input(2 for the first number, 1 for the secend number)

    NextNum:

        mov ah, 1
        int 21h

        cmp al, 13
        je compNum

        mov tempNum[bx], al
        inc bx

        loop NextNum

    compNum: ;turning the digits in temp to a number stored in cuurnt input state sellected by dh

        mov cx, bx
        mov bx, 0
        mov dl, 10

        nextDig:
            mov ah,0
            mov al, [si]

            mul dl
            mov [si],al

            sub tempnum[bx] , 48
            mov al, tempnum[bx]
            add [si], al

            inc bx

            loop nextDig
    cmp bp, 0

    je menuSellection:

        mov si, offset(secendNum);moving to the secend num

        ;print secend request for input
            mov dx, offset (secendNumMSG)
            mov ah, 9
            int 21h

        jmp num2


    menuSellection: ;checks what option was selected, if option not valid returns to start
        mov al,userSellection

        cmp al, '+'
        je addition

        cmp al, '-'
        je substruction

        cmp al, '*'
        je multiplication

        cmp al, '/'
        je divide

        cmp al, '%'
        je mod

        cmp al, '^'
        je pow

        jmp restartCalc

    ;calcules for each option
    addition:
        mov al, firstNum
        add al, secendNum
        mov result, al
        jmp showResult

    substruction:
        mov al, FirstNum
        sub al, secendNum
        mov result,al
        jmp showResult

    multiplication:
        mov al, firstNum
        mov ah,0
        mul secendNum
        mov result, al
        jmp showResult

    divide:
        mov al, firstNum
        mov ah, 0
        div secendNum
        mov result,al
        jmp showResult

    mod:
        mov al, firstNum
        mov ah, 0
        div secendNum
        mov result,ah
        jmp showResult

    pow:
        mov cl, secendNum
        mov ch, 0
        mov al, firstNum
        mov ah, 0
        dec cl
        nextPow:
            mul firstNum
            loop nextPow
        mov result, al
        jmp showResult

    ;prints the result in the correct length
    showResult:
        mov dx, offset (resultMsg)
        mov ah, 9
        int 21h

        mov al, result
        mov ah, 0
        mov dl,10
        div dl
        add ah,48
        mov tempNum[2],ah
        mov ah,0
        div dl
        add ah,48
        add al,48
        mov tempNum[1],ah
        mov tempNum[0],al

        mov ah,result ;finding length of result

        cmp ah, 10
        jb oneDigit

        cmp Ah, 100
        jb twoDigit

        jmp threeDigit

        oneDigit:    ;printing setting set accordingly
            mov cx, 1
            mov bx, 2
            jmp printNum

        twoDigit:
            mov cx, 2
            mov bx, 1
            jmp printNum

        threeDigit:
            mov cx,3
            mov bx,0
            jmp printNum

        printNum:    ;printing acoording to length.
            mov ah,2
            mov dl,tempNum[bx]
            int 21h
            inc bx
            loop printNum

    mov cx,4

    printSpaces:;prints spaces beetween runs of calculator
        mov ah, 2
        mov dl, 13
        int 21h
        mov ah, 2
        mov dl, 10
        int 21h
        loop printSpaces
        jmp restartCalc

    end:

    mov ax, 4c00h ; exit to operating system.
    int 21h
ends

end start