1 设计编写大小写字母转换程序实验，要求：程序有友好的运行界面；接收键盘输入字符，将其中的大小写字母相互转换为，其他非字母符号不变；要求程序有方便的输入输出功能；要求程序能够处理基本的错误信息；data segmentstr db Please enter a sentence $,0ah,0dherror db This is not a letter.,0ah,0dh,$sentence db 10h db ? 10h dup (?)data endscode segment assume cs:code,ds:datastart:mov ax,data mov ds,ax lea dx,str mov ah,9 int 21h mov ah,0ah int 21h lea di,sentence+2 mov cl,sentence+10hlop: mov al,di cmp al,0dh je exit cmp al,41h jb x0 cmp al,5ah jbe x1 cmp al,61h jb x0 cmp al,7ah jbe x2x0: mov dx,offset error mov ah,9 int 21h inc di loop lop jmp exitx1: add al,20 mov di,al inc di loop lop jmp exitx2: sub al,20 mov di,al inc di loop lopexit:mov byte ptr di,$ lea dx,sentence+2 mov ah,9 int 21h mov ah,4ch int 21hcode ends end start