bits 32 ; assembling for the 32 bits architecture

; declare the EntryPoint (a label defining the very first instruction of the program)
global start        

; declare external functions needed by our program
extern exit               ; tell nasm that exit exists even if we won't be defining it
import exit msvcrt.dll    ; exit is a function that ends the calling process. It is defined in msvcrt.dll
                          ; msvcrt.dll contains exit, printf and all the other important C-runtime specific functions

; our data is declared here (the variables needed by our program)
segment data use32 class=data
    ; ...
    a db 10
    b dw 2
    c db 3 
    d db 4
    x resw 1

; our code starts here
segment code use32 class=code
    start:
        ; ...
        mov ah,0
        mov al,[a]
        mul word [b]
        mov bl,[d]
        mov bh,0
        div bx
        mov bl,[c]    
        sub ax,bx
        mov [x],ax
        ; exit(0)
        push    dword 0      ; push the parameter for exit onto the stack
        call    [exit]       ; call exit to terminate the program
