CASE INVERT ALPHABETICALLY

.MODEL SMALL
.STACK 100H
.DATA
    A  DB  'Enter The Letter: $'
    B  DB  0DH,0AH,'The Expected Letter is: $'

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

     LEA DX, A
     MOV AH, 9
     INT 21H

     MOV AH, 1
     INT 21H
     MOV BL, AL

     CMP BL, "A"
     JB LOWERCASE
     CMP BL, "Z"
     JA LOWERCASE


     LEA DX, B
     MOV AH, 9
     INT 21H

     ADD BL, 33

     JMP END

     LOWERCASE:
     CMP BL, "a"
     JB END
     CMP BL, "z"
     JA END

     LEA DX,B
     MOV AH, 9
     INT 21H

     SUB BL, 31

     END:

     MOV AH, 2
     MOV DL, BL
     INT 21H

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