王爽<汇编语言>实验十一 (附测试代码)

 1 ;名称: letterc
 2 ;功能: 将以0为结尾的字符串中的小写字母转变成大写字母
 3 ;参数: ds:si指向字符串首地址
 4 
 5 assume cs:code
 6 
 7 data segment
 8         db "Beginner‘s All-purpose Symbolic Instruction Code.",0
 9 data ends
10 
11 code segment
12 main: 
13         mov ax,data
14         mov ds,ax
15         mov si,0
16         call letterc
17         
18         mov ax,4c00h
19         int 21h
20 letterc:
21         push ax
22         push ds
23         push si 
24         push cx
25         mov  ch,0
26 
27 lop:
28         mov cl,[si]
29         jcxz quit
30         cmp cl,‘z‘
31         ja  next
32         cmp cl,‘a‘
33         jb  next
34         and cl,11011111b
35         mov [si],cl
36 next:
37         inc si
38         jmp lop
39 quit:
40         pop cx
41         pop si
42         pop ds
43         pop ax
44         ret
45 code ends
46     end main