main.asm:5: error: parser: instruction expected

Question

I keep trying to run this but keep getting main.asm:5: error: parser: instruction expected - i have no idea why org isnt running or what ive done wrong but it wont run anymore. i used mycompiler.io to run it and others but no success. im very new to assembly and am struggling to trouble shoot errors like this

bits 16
            org      0x100 ; start offset at memory position 100
            jmp     main ; jump to main program
    ;
    ; Data definitions
    ;
    mess1: db 'Input any number (0 - 9)', 0dh,0ah,'$'
    mess2: db 'The number is a multiple of 3',0dh,0ah,'$'
    mess3: db 'The number is not a multiple of 3',0dh,0ah,'$'
    errmess: db '**',0dh,0ah,'$'
    crlf: db 0dh,0ah, '$'
    ; ; Display a string on the screen
    ; DX contains the address of the string
    ;
    display:
        mov     ah,09 
        int     21h 
        ret
    ;
    ; Set the cursor position
    ;
    cursor:
        mov     ah,02
        mov     bh,0 ; screen number 
        mov     dh,0ah ; row
        mov     dl,0 ; column
        int     10h
    ret
    ;
    ; Display a user prompt
    ;
    prompt:
        mov     dx,mess1
        call    display
        ret
    ;
    ; Read one character from the keyboard
    ;
    input:
    
        mov     ah,01
        int     21h
        ret
    ;
    ; Clear screen and change screen colour
    ;
    screen:
        mov     ah,06 ; scroll up screen
        mov     al,0 ; lines to scroll where 0 clear entire screen
        mov     cx,0 ; starting row:column
        mov     dl,80 ; ending row;column
        mov     dh,80
        mov     bh,17h ; change background color to white on blue
        int     10h
        ret
    ;
    ; Carriage returnm and line feed
    ;
    newline:
        mov     dx,crlf
        call    display
        ret
    ;
    ; Main program
    ;
    main:
        call    screen
        call    cursor
    next:
        call    prompt
        call    input
        cmp     al,'0'  ; character < 0?
        jl      error   ; yes, error message
        cmp     al,'9'  ; character > 9?
        jg      error   ; yes, error message
        sub     al,30h  ; convert from ASCII to numeric
        xor     ah,ah   ; clear AH
        mov     bl,3
        idiv    bl      ; divide by 3
        cmp     ah,0    ; remainder = n0?
        je      isdiv   ; yes: divisible by 3
        call    newline
        mov     dx,mess3 ; not divisible by 3
        call    display
        jmp     fin
    isdiv:
        call    newline
        mov     dx,mess2
        call    display ; divisible by 3
    fin:int     20h     ; terminate program
    ;
    ; Display error message. Number out of range
    ;
    error:
        mov dx,errmess
        call display
        jmp next

Answer 1

It seems that the NASM IDE on mycompiler.io is for 64 bit assembly. The code you have is 16 bit (I'd stick with the 16 bit if you are learning assembly as a hobby, it can be much more forgiving and is great for learning). Unfortunately the 16 bit code cannot compile natively for 64 bit systems. If you want to run this and other 16 bit code you need NASM and something to run 16 bit code in, I recommend dosbox .

To compile and run your code:

nasm mycode.asm -fbin -o run.com
dosbox main.com

(If you go the dosbox route and are on windows make sure to add dosbox.exe to path so you can do this from command prompt)

If you are looking for an online solution, you can use repl.it to compile with nasm by creating a bash project and using nasm mycode.asm -fbin -o run.com to build. Also on repl.it is this web version of dosbox. I have not personally used it much but it seems to work fine.

Good luck on your assembly journey!