为什么跳到错误的地方？

Question

我写了以下代码来测试用户输入是否在0和9之间。
不幸的是，当用户输入q或s或u时，它将跳转到cont。
PS：inv和cont是标签。

.model small 
.stack 
.data 
    msg db 0ah,0dh,'Enter TWO odd integer values (0 to 9): $' 
    invalid db 0ah,0dh,'The number is not an odd number.$' 
    firstnum db ? 
    secondnum db ? 
    result db 0ah,0dh,'The average of the input values is: $' 
.code 
main proc 
    mov ax,@data 
    mov ds,ax 
loopin: 
    mov ah,09h 
    lea dx,msg 
    int 21h 

    mov ah,01h 
    int 21h 

    sub al,30h 
    mov firstnum,al 

    sub ah,ah 
    mov bl,2 
    div bl 
    cmp ah,0 
    je inv 
    jmp cont 
inv: 
    mov ah,09h 
    lea dx,invalid 
    int 21h 
    jmp loopin 
cont: 
    mov ah,02h 
    mov dl,',' 
    int 21h 

    mov ah,01h 
    int 21h 

    sub al,30h 
    mov secondnum,al 

    sub ah,ah 
    mov bl,2 
    div bl 
    cmp ah,0 
    je inv 

    sub ah,ah 
    mov al,firstnum 
    add al,secondnum 
    mov bl,2 
    div bl 
    mov bh,ah 

    mov ah,09h 
    lea dx,result 
    int 21h 

    add al,30h 
    mov ah,02h 
    mov dl,al 
    int 21h 

    mov ah,02h 
    mov dl,'.' 
    int 21h 

    sub ah,ah 
    mov al,bh 
    mov bl,5 
    mul bl 
    add al,30h 

    mov ah,02h 
    mov dl,al 
    int 21h 

    mov ah,4ch 
    int 21h 
main endp 
end main 

Answer 1

这应该是你的测试代码吗？

sub al,30h 
mov firstnum,al 

sub ah,ah 
mov bl,2 
div bl 
cmp ah,0 
je inv 
jmp cont 

绝对不会检查输入是一个数字。试试这个：

sub al,30h 
jb notanumber 
cmp al,9 
ja notanumber 
mov firstnum,al 
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