; example of simplified Win32 programming using complex macro features
include "win32ax.inc"

.data
wc WNDCLASSEX                                      ; create local variables on stack
msg MSG 
hwnd dw 0


.code

start:
proc _Main
    mov   wc.cbSize,sizeofsdsd WNDCLASSEX                  ; fill values in members of wc
    mov   wc.style, CS_HREDRAW | CS_VREDRAW
    mov   wc.lpfnWndProc, asdddddddd
    mov   wc.cbClsExtra,NULL 
    mov   wc.cbWndExtra,NULL 
    push  hInstance
    pop   wc.hInstance 
    mov   wc.hbrBackground,COLOR_WINDOW+1 
    mov   wc.lpszMenuName,NULL 
    mov   wc.lpszClassName,ClassName 
    invoke LoadIcon,NULL,IDI_APPLICATION 
    mov   wc.hIcon,eax 
    mov   wc.hIconSm,eax 
    invoke LoadCursor,NULL,IDC_ARROW
    mov   wc.hCursor,eax 
    invoke RegisterClassEx, wc                       ; register our window class 
    invoke CreateWindowEx,NULL,\ 
                ADDR ClassName,\ 
                ADDR AppName,\ 
                WS_OVERLAPPEDWINDOW,\ 
                CW_USEDEFAULT,\ 
                CW_USEDEFAULT,\ 
                CW_USEDEFAULT,\ 
                CW_USEDEFAULT,\ 
                NULL,\ 
                NULL,\ 
                hInst,\ 
                NULL 
    mov   hwnd,eax 
    invoke ShowWindow, hwnd,CmdShow               ; display our window on desktop 
    invoke UpdateWindow, hwnd    

        invoke CreateWindow
        invoke DialogBoxParam,NULL,IDD_DLG1001,NULL,DLG_Function,NULL
        invoke  MessageBox,HWND_DESKTOP,"Hi! I'm the example program!","Win32 Assembly",MB_OK
        invoke  ExitProcess,0
ret
endp

proc DLG_Function,hwnd,uMesg,wParam,lParam

ret
endp

.end start

;section '.rsrc'  data readable resource from 'rc.res'
    

I've got some code below which I expected Fasm to catch error on compilation but it didn't.

(...)

I've added many undeclared symbol to the code but strangely, fasm compiles sucessfully to whatever what you type into.

call _Main