匯編語言(王爽 第三版)實驗十一

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
    mov ax,4c00h
    int 21h
letterc:push ax
    push si
s:    mov al,ds:[si]
    cmp al,0
    je ok
    cmp al,'a'
    jb next
    cmp al,'z'
    ja next

change:    and al,11011111b
    mov ds:[si],al
    
next:    inc si
    loop s

ok:    pop si
    pop ax
    ret
    
code ends
end begin