A Simple Win32 GUI Introduction

#include <windows.h> /* Windows header */

LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);
char szClassName[ ] = "WindowsApp";   /* Class ID */

int WINAPI
WinMain (HINSTANCE hThisInstance,
         HINSTANCE hPrevInstance,
         LPSTR lpszArgument,
         int nFunsterStil)

{
    HWND hwnd;            
    MSG messages;          
    WNDCLASSEX wincl;      

    wincl.hInstance = hThisInstance;
    wincl.lpszClassName = szClassName;
    wincl.lpfnWndProc = WindowProcedure; /* See end of code */      
    wincl.style = CS_DBLCLKS;                 
    wincl.cbSize = sizeof (WNDCLASSEX);
    wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
    wincl.lpszMenuName = NULL;                
    wincl.cbClsExtra = 0;                      
    wincl.cbWndExtra = 0;                 
    wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND; /* Default windows background colour */

    if (!RegisterClassEx (&wincl))
        return 0;

    hwnd = CreateWindowEx (
           0,                   
           szClassName,         /* Classname */
           "Windows App",       /* Title Text */
           WS_OVERLAPPEDWINDOW, 
           CW_USEDEFAULT,       /* Default x... */
           CW_USEDEFAULT,       /* ...and default y position of window */
           640,                 /* The programs width... */
           480,                 /* ...and height in pixels */
           HWND_DESKTOP,        
           NULL,               
           hThisInstance,       
           NULL                 
           );

    /* Make the window visible on the screen */
    ShowWindow (hwnd, nFunsterStil);
    while (GetMessage (&messages, NULL, 0, 0))
    {
        TranslateMessage(&messages);
        DispatchMessage(&messages);
    }

    /* Return: wParam from a quit message usually = 0 */
    return messages.wParam;
}

LRESULT CALLBACK
WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{ /* Called when window processes a message */
    switch (message)                 
    {
        case WM_DESTROY: /* Destoy message: called if you press the "x" in the top right corner */
            PostQuitMessage (0); /* Send a message to quit */       
            break;
        default:                     
            return DefWindowProc (hwnd, message, wParam, lParam);
    }
    return 0;
}