FIRST & LAST CAPITAL

.MODEL SMALL
.STACK 100H
.DATA
   TEXT  DB  'Enter a line of text : $'
   FIRST_CAP  DB  0DH,0AH,'First Capital Letter : $'
   LAST_CAP  DB  0DH,0AH,'Last Capital Letter  : $'

   FLAG          DB  0
   FIRST_LETTER  DB  5BH
   LAST_LETTER   DB  40H

.CODE
  MAIN PROC
     MOV AX, DATA
     MOV DS, AX

     LEA DX, TEXT
     MOV AH, 9
     INT 21H

     MOV AH, 1

     INPUT:
       INT 21H

       MOV BL, AL

       CMP BL, 0DH
       JE END_INPUT

       CMP BL, "A"
       JL INPUT

       MOV FLAG, 1

       CMP BL, "Z"
       JG INPUT

       CMP BL, FIRST_LETTER
       JG NEXT
       MOV FIRST_LETTER, BL

       NEXT:
         CMP BL, LAST_LETTER
         JL INPUT
         MOV LAST_LETTER, BL

     JMP INPUT

     END_INPUT:

     CMP FLAG, 1
     JE DISPLAY

     JMP END

     DISPLAY:
       LEA DX,FIRST_CAP
       MOV AH, 9
       INT 21H

       MOV AH, 2
       MOV DL, FIRST_LETTER
       INT 21H

       LEA DX,LAST_CAP
       MOV AH, 9
       INT 21H

       MOV AH, 2
       MOV DL, LAST_LETTER
       INT 21H

     END:

     MOV AH, 4CH
     INT 21H
   MAIN ENDP
 END MAIN