windows随即产生多个矩形(Rectangle)

/*----------------------------------------------------------------------RANDRECT.C -- Displays Random Rectangles-----------------------------------------------------------------------*/#include <windows.h>#include <stdlib.h>// for the rand functionLRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;void DrawRectangle (HWND) ;int cxClient, cyClient ;int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,PSTR szCmdLine,int iCmdShow) {static TCHAR szAppName[] = TEXT ("RandRect") ;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 (NULL, IDI_APPLICATION) ;wndclass.hCursor = LoadCursor (NULL, IDC_ARROW) ;wndclass.hbrBackground= (HBRUSH) GetStockObject (WHITE_BRUSH) ;wndclass.lpszMenuName= NULL ;wndclass.lpszClassName= szAppName ;if (!RegisterClass (&wndclass)) {MessageBox (NULL, TEXT ("This program requires Windows NT!"),szAppName, MB_ICONERROR) ;return 0 ;}hwnd = CreateWindow (szAppName, TEXT ("Random Rectangles"),WS_OVERLAPPEDWINDOW,CW_USEDEFAULT, CW_USEDEFAULT,CW_USEDEFAULT, CW_USEDEFAULT,NULL, NULL, hInstance, NULL) ;ShowWindow (hwnd, iCmdShow) ;UpdateWindow (hwnd) ;while (TRUE) {if (PeekMessage (&msg, NULL, 0, 0, PM_REMOVE)) {if (msg.message == WM_QUIT)break ;TranslateMessage (&msg) ;DispatchMessage (&msg) ;} elseDrawRectangle (hwnd) ;}return msg.wParam ;}LRESULT CALLBACK WndProc (HWND hwnd, UINT iMsg, WPARAM wParam, LPARAM lParam) {switch (iMsg) {case WM_SIZE:cxClient = LOWORD (lParam) ;cyClient = HIWORD (lParam) ;return 0 ;case WM_DESTROY:PostQuitMessage (0) ;return 0 ;}return DefWindowProc (hwnd, iMsg, wParam, lParam) ;}void DrawRectangle (HWND hwnd) {HBRUSH hBrush ;HDC hdc ;RECT rect ;if (cxClient == 0 || cyClient == 0)return ;SetRect (&rect, rand () % cxClient, rand () % cyClient,rand () % cxClient, rand () % cyClient) ;hBrush = CreateSolidBrush (RGB (rand () % 256, rand () % 256, rand () % 256)) ;hdc = GetDC (hwnd) ;FillRect (hdc, &rect, hBrush) ;ReleaseDC (hwnd, hdc) ;DeleteObject(hBrush);}