Write a program in assembly language to reverse a string.

; Write a program to reverse a string.

.MODEL SMALL
.STACK 100H
.DATA     
    INPUT_MSG DB 'ENTER A STRING: $'
    OUTPUT_MSG DB 0AH,0DH,'OUTPUT IS: $'
.CODE

MAIN PROC

    MOV AX,@DATA
    MOV DS,AX
   
    MOV AH, 9
    LEA DX, INPUT_MSG
    INT 21H
   
    MOV AH,1
   
    MOV CX, 0  ;CX is 0
    TOP:
       
        INT 21H
   
        CMP AL,0DH   ; the comparison with carriage return done to find the end of a string
        JE END_INPUT
   
        PUSH AX
        INC CX
        JMP TOP
   
    END_INPUT:

    MOV AH,9
    LEA DX,OUTPUT_MSG
    INT 21H
   
    MOV AH, 2

    OUTPUT:
        POP DX
        INT 21H
        LOOP OUTPUT
   
    EXIT:
    MOV AH,4CH
    INT 21H
    MAIN ENDP
END MAIN