王爽汇编第二版实验11

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编写一个程序，将包含任意字符，以0结尾的字符串中的小写字母变为大写

assume cs:code

data segment
   db "Beginner's All-purpose Symbolic Instruction Code.",0
data ends

code segment
   begin:   mov ax,data
           mov ds,ax
           mov si,0
           call letterc   ;将小写字母变为大写

           ;在屏幕5行3列输出
           mov dh,5
           mov dl,3
           call print
           mov ax,4c00h
           int 21h

   letterc:   push ds
               push si
               push cx

   letterStart:
               mov cl,ds:[si]
               mov ch,0
               jcxz letterEnd
               cmp cx,'a'
               jb letterChange
               cmp cx,'z'
               ja letterChange
               and cl,11011111b
               mov ds:[si],cl
   letterChange:
                   inc si
                   jmp letterStart
   letterEnd:
                   pop cx
                   pop si
                   pop ds
                   ret

   print:   push es
           push di
           push si
           push ax
           push dx
           push cx

   printStart:
               mov ax,0b800h
               mov es,ax

               mov al,160
               mov ah,0
               mul dh
               push ax
               mov al,2
               mov ah,0
               mul dl
               pop dx
               add ax,dx
               mov di,ax



   printRun:
               mov cl,ds:[si]
               mov ch,0
               jcxz printEnd
               mov es:[di],cl
               inc di
               mov byte ptr es:[di],36
               inc di
               inc si
               jmp printRun

   printEnd:
               pop cx
               pop dx
               pop ax
               pop si
               pop di
               pop es
               ret
code ends
end begin