;CASE CONVERSION PROGRAM

.MODEL SMALL
.STACK 100H
.DATA
 X DB ?
 MSG1 DB "ENTER INPUT: $"
 MSG2 DB 0DH,0AH, "ENTERED CHARACTER IS: $"
 MSG3 DB 0DH,0AH, "INVALID CHARACTER $"
.CODE
    MAIN PROC
          MOV AX,@DATA ;LOAD DATA SEGMENT
          MOV DS,AX

          LEA DX,MSG1  ;PRINT MSG1
          MOV AH,9
          INT 21H

          MOV AH,1     ;INPUT CHAR
          INT 21H
          MOV X,AL

          LEA DX,MSG2  ;PRINT MSG2
          MOV AH,9
          INT 21H

          CMP X,65             ;COMPARE IF VALID ALPHABET
          JGE LABEL1


          LEA DX,MSG3  ;ELSE PRINT INVALID CHAR
          MOV AH,9
          INT 21H
          JMP EXIT
              .

          LABEL1:
          CMP X,90
          JLE CONVERT_TO_LOWER   ; IF RANGE IS BETWEEN 65<X<90

          CMP X,97             ;LOWERCASE
          JGE LOWERCASE_LABEL

          LEA DX,MSG3  ; ELSE PRINT INVALID CHAR
          MOV AH,9
          INT 21H
          JMP EXIT

          LOWERCASE_LABEL:
          CMP X,122
          JLE CONVERT_TO_UPPER

          CONVERT_TO_UPPER:          ;LOWER TO UPPER CONVERSION
          MOV AH,2
          SUB X,32
          MOV DL,X
          INT 21H
          JMP EXIT

          CONVERT_TO_LOWER:    ;UPPER TO LOWER CONVERSION

          MOV AH,2
          ADD X,32
          MOV DL,X
          INT 21H


          EXIT:
          MOV AH,4CH ;RETURN TO DOS
          INT 21H
        MAIN ENDP

    END MAIN