Here is the code im using:

extern(Windows)
LRESULT WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) nothrow
{
    scope (failure) assert(0);

    HDC hdc;
    PAINTSTRUCT ps;
    RECT rect;

    switch (message)
    {
        case WM_CREATE:
             CreateWindow("BUTTON".toUTF16z,      // window class name
                         "The Hello Program",  // window caption
                         WS_CHILD | WS_VISIBLE,  // window style
                         CW_USEDEFAULT,        // initial x position
                         CW_USEDEFAULT,        // initial y position
                         250,        // initial x size
                         250,        // initial y size
                         hwnd,                 // parent window handle
                         0,                 // window menu handle
                         NULL,            // program instance handle
                         NULL);
                         return 0;
        case WM_COMMAND:
        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;

        default:
    }

    return DefWindowProc(hwnd, message, wParam, lParam);
}


This gives an error saying: Cannot pas argument of type 'int' to argument of type 'void*'. How is this fixed?

On Wednesday, 9 December 2020 at 17:25:10 UTC, Ruby The Roobster wrote:
>              CreateWindow("BUTTON".toUTF16z,      // window class name

fyi for a string literal like this you can just do

"BUTTON"w.ptr // note the w

> This gives an error saying: Cannot pas argument of type 'int' to argument of type 'void*'. How is this fixed?

Use lowercase `null` instead.

On Wednesday, 9 December 2020 at 17:32:57 UTC, Adam D. Ruppe wrote:
> On Wednesday, 9 December 2020 at 17:25:10 UTC, Ruby The Roobster wrote:
>>              CreateWindow("BUTTON".toUTF16z,      // window class name
>
> fyi for a string literal like this you can just do
>
> "BUTTON"w.ptr // note the w
>
>> This gives an error saying: Cannot pas argument of type 'int' to argument of type 'void*'. How is this fixed?
>
> Use lowercase `null` instead.

It's not the 'NULL' that's the error. It doesn't compile because of the '0'
. That is what I need to fix, since I want to make a WM_COMMAND for that button.

On Wednesday, 9 December 2020 at 17:37:16 UTC, Ruby The Roobster wrote:
> It's not the 'NULL' that's the error.

I know.

> It doesn't compile because of the '0'
> . That is what I need to fix, since I want to make a WM_COMMAND for that button.

Use lowercase `null` instead.

On Wednesday, 9 December 2020 at 17:42:50 UTC, Adam D. Ruppe wrote:
> On Wednesday, 9 December 2020 at 17:37:16 UTC, Ruby The Roobster wrote:
>> It's not the 'NULL' that's the error.
>
> I know.
>
>> It doesn't compile because of the '0'
>> . That is what I need to fix, since I want to make a WM_COMMAND for that button.
>
> Use lowercase `null` instead.

I did. Still gives an error:

LRESULT WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) nothrow
{
    scope (failure) assert(0);

    HDC hdc;
    PAINTSTRUCT ps;
    RECT rect;

    switch (message)
    {
        case WM_CREATE:
             CreateWindow("BUTTON".toUTF16z,      // window class name
                         "The Hello Program",  // window caption
                         WS_CHILD | WS_VISIBLE,  // window style
                         CW_USEDEFAULT,        // initial x position
                         CW_USEDEFAULT,        // initial y position
                         250,        // initial x size
                         250,        // initial y size
                         hwnd,                 // parent window handle
                         0,                 // window menu handle
                         null,            // program instance handle
                         null);
                         return 0;
        case WM_COMMAND:
        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;

        default:
    }

    return DefWindowProc(hwnd, message, wParam, lParam);
}

Also, here is the error in full: E:\Users\User\Desktop\tet.d|100|       cannot pass argument `0` of type `int` to parameter `void* i`|

On Wednesday, 9 December 2020 at 17:45:18 UTC, Ruby The Roobster wrote:
>                          0,                 // window menu

here, that's the only int you do and I'm pretty sure that's supposed a be a HMENU which is a HANDLE, which is a void* rather than an int.

C will cast 0 to null implicitly, D will not. If there's ever a case where you need to pass a number as a handle (like some HBRUSHe among others), you then explicitly cast it like `cast(HANDLE) -1`. (HANDLE is an alias to void* too so that would also work)

But for 0 you almost certainly just want to get in the habit of using the built in `null` instead 0.

re NULL vs null, both are OK here, but since NULL can actually be overridden by other libs (it is just a library constant) you're better off consistently using `null` for those too.

On Wednesday, 9 December 2020 at 17:57:49 UTC, Adam D. Ruppe wrote:
>
> C will cast 0 to null implicitly, D will not. If there's ever a case where you need to pass a number as a handle (like some HBRUSHe among others), you then explicitly cast it like `cast(HANDLE) -1`. (HANDLE is an alias to void* too so that would also work)

Thank you. Now it works.