format PE GUI 4.0 ;file type, win32 portable executable

include '%fasminc%\win32a.inc' ;for macros, constants

section '.data' readable writeable ;variables
    caption db 'hello world!',0
    title db 'flat assembler',0

section '.code' code executable readable ;code begins here
  start:
        invoke    0,text,caption,MB_INFORMATION+MB_OK ;call MessageBoxA
        invoke    ExitProcess,0 ;exit program

section '.idata' import data readable writeable ;win32 functions used
  library kernel,'KERNEL32.DLL',\
          user,'USER32.DLL'

  import kernel,\
         ExitProcess,'ExitProcess'

  import user,\
         MessageBox,'MessageBoxA'