getNum

getNum proc
    push ax
    push bx
    push cx
    push dx
    mov cl, 0 ;How many digits
    mov bx, 0 ;Holds the number
    nextDigit:
    mov ah, 1 ;Get char
    int 21h
    cmp al, 13 ;If enter end
    je return
    sub al, 48
    jc noDigit
    cmp al, 9
    jbe yesDigit
    noDigit:
        call delete
        jmp nextDigit
    yesDigit:
        inc cl
        mov dx, 10
        mov ah, 0
        push ax ;Save ax
        mov ax, bx
        mul dx
        mov bx, ax
        pop ax
        add bx, ax
        cmp cl, 4
        jne nextDigit
    return:
    mov answer, bx
    pop dx
    pop cx
    pop bx
    pop ax
    ret
getNum endp

delete proc
    push ax
    push dx
    mov ah, 2
    mov dl, 08h ;Backspace
    int 21h
    mov ah, 2
    mov dl, 00h ;null
    int 21h
    mov ah, 2
    mov dl, 08h ;Backspace
    int 21h
    pop dx
    pop ax
    ret
delete endp