Problem 1

.MODEL SMALL
.STACK 100H

 .DATA
   PROMPT_1  DB  'Enter a line of text : $'
   PROMPT_2  DB  0DH,0AH,'Output : $'
   PROMPT_4  DB  0DH,0AH,' *****  No Capital Letters  *****$'

   FLAG          DB  0
   FIRST_LETTER  DB  5BH
   LAST_LETTER   DB  40H

 .CODE
   MAIN PROC
     MOV AX, @DATA                ; initialize DS
     MOV DS, AX

     LEA DX, PROMPT_1             ; load and display the string PROMPT_1
     MOV AH, 9
     INT 21H

     MOV AH, 1                    ; set input function

     @INPUT:                      ; jump label
       INT 21H                    ; read a character

       MOV BL, AL                 ; set BL=AL

       CMP BL, 0DH                ; compare BL with CR
       JE @END_INPUT              ; jump to label @END_INPUT if BL=CR

       CMP BL, "A"                ; compare BL with "A"
       JL @INPUT                  ; jump to label @INPUT if BL<A

       MOV FLAG, 1                ; set FLAG=1

       CMP BL, "Z"                ; compare BL with "Z"
       JG @INPUT                  ; jump to label @INPUT if BL>Z

       CMP BL, FIRST_LETTER       ; compare BL with variable FIRST_LETTER
       JG @NEXT                   ; jump to label @NEXT if BL>FIRST_LETTER
       MOV FIRST_LETTER, BL       ; set FIRST_LETTER=BL

       @NEXT:                     ; jump label
         CMP BL, LAST_LETTER      ; compare BL with variable LAST_LETTER
         JL @INPUT                ; jump to label @INPUT if BL<LAST_LETTER
         MOV LAST_LETTER, BL      ; set LAST_LETTER=BL

     JMP @INPUT                   ; jump to label @INPUT

     @END_INPUT:                  ; jump label

     CMP FLAG, 1                  ; compare FLAG with 1
     JE @DISPLAY                  ; jump to label @DISPLAY if FLAG=1

     LEA DX, PROMPT_4             ;  load and display the string PROMPT_4
     MOV AH, 9
     INT 21H

     JMP @END                     ; jump to label @END

     @DISPLAY:                    ; jump label
       LEA DX, PROMPT_2           ; load and display the string PROMPT_2
       MOV AH, 9
       INT 21H

       MOV AH, 2                  ; set output function
       MOV DL, FIRST_LETTER       ; set DL=FIRST_LETTER
       INT 21H                    ; print a character


       MOV AH, 2                  ; set output function
       MOV DL, LAST_LETTER        ; set DL=LAST_LETTER
       INT 21H                    ; print a character


     @END:                        ; jump label

     MOV AH, 4CH                  ; return control to DOS
     INT 21H
   MAIN ENDP
 END MAIN