dseg    segment str_source  db "HelloWorld$"str1        db 20 dup(0)str2        db 20 dup(0)int_caption db 0int_lower   db 0dseg    ends cseg    segment                         ;设置代码段        assume   cs:cseg,ds:dsegstart:         mov ax , dseg                   ;初始化ds        mov ds , ax        mov si , offset str_source      ;offset str_source-->si 变址        xor ax , ax        push ax        push ax                         ;str1,str2指针入栈read_loop:        mov al , [si]                   ;取[si]中的内容，即偏移量        cmp al , ‘$‘        je  exit        cmp al , ‘Z‘        ja  lower_case        pop di                          ;大写        mov al , [si]        mov [di] , al        inc di        push di        inc int_caption                        inc si        jmp read_loop  lower_case:                             ;小写        inc int_lower        inc si        jmp read_loop  exit:           mov dl , int_caption        add dl , 30h        mov ah , 02h        int 21h        mov dl , 0ah                    ;回车换行        mov ah , 02h        int 21h        mov dl , 0dh        mov ah , 02h        int 21h        mov dl , int_lower        add dl , 30h        mov ah , 02h        int 21h        mov dl , 0ah                    ;回车换行        mov ah , 02h        int 21h        mov dl , 0dh        mov ah , 02h        int 21h        pop di        mov al ,‘$‘        mov [di] , al        mov dl , offset str1        mov ah , 09h        int 21h        mov ax , 4c00h                  ;返回DOS        int 21h                    cseg    ends                            ;代码段结束end     start                           ;汇编语言源程序结束