王爽<汇编语言>实验十一 (附测试代码)

;名称: letterc
;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
;参数: ds:si指向字符串首地址

assume cs:code

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

code segment
main:
mov ax,data
mov ds,ax
mov si,0
call letterc

mov ax,4c00h
int 21h
letterc:
push ax
push ds
push si
push cx
mov  ch,0

lop:
mov cl,[si]
jcxz quit
cmp cl,'z'
ja  next
cmp cl,'a'
jb  next
and cl,11011111b
mov [si],cl
next:
inc si
jmp lop
quit:
pop cx
pop si
pop ds
pop ax
ret
code ends
end main