getting Win32 Messagebox to work

[Mark Moorhen]

Hi,

I've recently started looking into D, and I'm afraid i'm gonna 
need some support to get me going.

I work mostly on Windows, so i've downloaded the examples from 
"https://github.com/AndrejMitrovic/DWinProgramming". Only these 
examples do not work out-of-the-box on my machine (Win10, 64-bit 
/ DMD32 D Compiler v2.082.0)

Now I'm trying to pass the content for a Messagebox as a variable 
like this:
<code>
import core.runtime;
import win32.windef;
import win32.winuser;

extern (Windows)
void WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR 
lpCmdLine, int iCmdShow)
{
		string content = "Some random content.";
         MessageBox(NULL, content , "Window title", 0);
}
</code>

When compiling I get the error:

HelloMsg.d(9): Error: function `win32.winuser.MessageBoxA(void*, 
const(char)*, const(char)*, uint)` is not callable using argument 
types `(typeof(null), string, string, int)`
HelloMsg.d(9):        cannot pass argument `content` of type 
`string` to parameter `const(char)*`

Can anyone help me out with this?