main

#include <windows.h>
#include "resource.h"

LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
                    PSTR szCmdLine, int iCmdShow)
{
     TCHAR    szAppName[] = TEXT ("IconDemo") ;
     HWND     hwnd ;
     MSG      msg ;
     WNDCLASS wndclass ;

     wndclass.style         = CS_HREDRAW | CS_VREDRAW ;
     wndclass.lpfnWndProc   = WndProc ;
     wndclass.cbClsExtra    = 0 ;
     wndclass.cbWndExtra    = 0 ;
     wndclass.hInstance     = hInstance ;
     wndclass.hIcon         = LoadIcon (hInstance, MAKEINTRESOURCE (IDI_ICON)) ;
     wndclass.hCursor       = LoadCursor (NULL, IDC_ARROW) ;
     wndclass.hbrBackground = (HBRUSH)GetStockObject (WHITE_BRUSH) ;
     wndclass.lpszMenuName  = NULL ;
     wndclass.lpszClassName = szAppName ;

     if (!RegisterClass (&wndclass))
     {    // UNICODE-Compilierung ist die einzige realistische Fehlermöglichkeit 
          MessageBox (NULL, TEXT ("Programm arbeitet mit Unicode und setzt Windows NT voraus!"), 
                      szAppName, MB_ICONERROR) ;
          return 0 ;
     }

     hwnd = CreateWindow (szAppName, TEXT ("Icon-Demo"),
                          WS_OVERLAPPEDWINDOW,
                          CW_USEDEFAULT, CW_USEDEFAULT,
                          CW_USEDEFAULT, CW_USEDEFAULT,
                          NULL, NULL, hInstance, NULL) ;

     ShowWindow (hwnd, iCmdShow) ;
     UpdateWindow (hwnd) ;

     while (GetMessage (&msg, NULL, 0, 0))
     {
          TranslateMessage (&msg) ;
          DispatchMessage (&msg) ;
     }
     return msg.wParam ;
}

LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
     static HICON hIcon ;
     static int   cxIcon, cyIcon, cxClient, cyClient ;
     HDC          hdc ;
     HINSTANCE    hInstance ;
     PAINTSTRUCT  ps ;
     int          x, y ;

     switch (message)
     {
     case WM_CREATE :
          hInstance = ((LPCREATESTRUCT) lParam)->hInstance ;
          hIcon = LoadIcon (hInstance, MAKEINTRESOURCE (IDI_ICON)) ;
          cxIcon = GetSystemMetrics (SM_CXICON) ;
          cyIcon = GetSystemMetrics (SM_CYICON) ;
          return 0 ;

     case WM_SIZE :
          cxClient = LOWORD (lParam) ;
          cyClient = HIWORD (lParam) ;
          return 0 ;

     case WM_PAINT :
          hdc = BeginPaint (hwnd, &ps) ;

          for (y = 0 ; y < cyClient ; y += cyIcon)
               for (x = 0 ; x < cxClient ; x += cxIcon)
                    DrawIcon (hdc, x, y, hIcon) ;

               EndPaint (hwnd, &ps) ;
               return 0 ;

     case WM_DESTROY :
          PostQuitMessage (0) ;
          return 0 ;
     }
     return DefWindowProc (hwnd, message, wParam, lParam) ;
}

ICONDEMO.RC:

#include "resource.h"
IDI_ICON ICON DISCARDABLE "icondemo.ico"

resource.h:

#define IDI_ICON 101

ICONDEMO.ICO gibts natürlich...