masm - Checking if two strings are equal in assembly -

the program check if user entered password matches 1 specified directly in program. not able understand why happen 'password incorrect' when try input directly keyboard. when specifying 'src' directly in program output seems perfect though.

.model small .stack 1000h  disp macro msg ;macro display string of characters lea dx,msg mov ah,09h int 21h endm  input macro ;macro input character character mov ah,01h int 21h endm  data segment  cr equ 0dh lf equ 0ah msg db 'enter password please : ',cr,lf,'$' tru db 'password correct$' fal db 'password incorrect$' src db 10 dup('$') dest db 'yo$'  len equ ($-dest) data ends    code segment assume cs:code,ds:data,es:data start:  mov ax,data     mov ds,ax     mov es,ax     mov si,offset src     mov di,offset dest       cld     mov cx,len     xor bx,bx     disp msg re: input     mov [si],al     inc si     inc bx     cmp al,cr     jne re      cmp bx,cx ;if string lengths dont match strings unequal     jne l1      mov si,offset src     repe cmpsb     jnz l1 l2: disp tru     jmp exit l1: disp fal exit:   mov ah,4ch     int 21h code    ends     end start 

your check whether read character carriage return placed after character has been written src buffer. when compare 2 strings later on, src contain cr character dest doesn't contain.

that is, if entered yo you'll have dest = 'yo$', src = 'yo\r', , len = 3.

here's modified version of input loop works (new code in lowercase):

re: input     cmp al,cr     je got_input  ; exit loop if read cr character     mov [si],al     inc si     inc bx     jmp re got_input:     inc bx     ; len includes '$' character after 'yo', increase bx 1 match     cmp bx,cx  ; if string lengths dont match strings unequal