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
