Program: This program compares a pair of characters entered by keyboard.

; Registers used: AX, BX, CX, DX

DATA SEGMENT

                         XX DB?

                        YY DB?

DATA ENDS

CODE SEGMENT

                        ASSUME     CS:  CODE,   DS: DATA

MAINP:                       MOV AX, DATA; initialize data

                                    MOV DS, AX; segment using AX

                                    MOV CX, 03H; set counter to 3.

NEXTP:                      MOV AH, 01H; Waiting for user to enter a char.

                        INT    21H        

                                    MOV XX, AL; store the 1^st input character in XX

                                    MOV AH, 01H; waiting for user to enter second 

                                    INT     21H   ;   character.

                                    MOV YY, AL; store the character to YY

                                    MOV BH, XX; load first character in BH

                                    MOV BL, YY; load second character in BL

                                    CMP BH, BL; compare the characters

                                    JNE NOT_EQUAL; 

EQUAL:                     MOV AH, 02H; if characters are equal then control 

                                    MOV DL, 'Y'    ; will execute this block and

                                    INT    21H   ; display 'Y'

                                    JMP CONTINUE; Jump to continue loop.

NOT_EQUAL:           MOV AH, 02H; if characters are not equal then

Control

                                    MOV DL, 'N''   ; will execute this block and

                                    INT 21 H    ; display 'N'

CONTINUE:              LOOP NEXT P   ; Get the next character

                                    MOV AH, 4C H; Exit to DOS

                                    INT 21 H

CODE ENDS

END MAINP