Data Segment
  stri db 'this is my first exercise$'
  stri1 db '  $'
  temp db ?
Data Ends
;---------------------------------------------------------------;
Stk Segment Stack
  db 100 dup(?)
Stk Ends
;---------------------------------------------------------------;
Code Segment 
Assume Cs:Code,Ds:Data,ss:Stk
Start:mov ax,Data
      mov ds,ax
      mov ax,Stk
      mov ss,ax
      mov sp,100
;---------------------------------------------------------------;
      mov ah,9      
      mov dx,offset stri
      int 21h
      mov ah,9
      mov dx,offset stri1
      int 21h                           
;---------------------------------------------------------------;
      mov si,24
      mov bx,0
 AFUH:mov al,stri[bx]
      mov temp,al
      mov al,stri[si]
      mov stri[bx],al
      mov al,temp
      mov stri[si],al
      inc bx
      dec si
      cmp si,bx
      jne AFUH           
;---------------------------------------------------------------;
      mov ah,9     
      mov dx,offset stri          
      int 21h
;---------------------------------------------------------------;
      mov ah,1
      int 21h
      mov ah,4ch
      int 21h     
Code Ends
End Start