ShowWindowがないのになぜ表示される?

WindowsAPI
1#include<windows.h>
2
3LRESULT CALLBACK WndProc(HWND hwnd , UINT msg , WPARAM wp , LPARAM lp) {
4	switch (msg) {
5	case WM_DESTROY:
6		MessageBox(hwnd , TEXT("終わるにゃん") ,
7			 TEXT("Kitty") , MB_ICONINFORMATION);
8		PostQuitMessage(0);
9		return 0;
10	}
11	return DefWindowProc(hwnd , msg , wp , lp);
12}
13
14int WINAPI WinMain(HINSTANCE hInstance , HINSTANCE hPrevInstance ,
15		 PSTR lpCmdLine , int nCmdShow ) {
16	HWND hwnd;
17	MSG msg;
18	WNDCLASS winc;
19
20	winc.style		= CS_HREDRAW | CS_VREDRAW;
21	winc.lpfnWndProc	= WndProc;
22	winc.cbClsExtra	= winc.cbWndExtra	= 0;
23	winc.hInstance		= hInstance;
24	winc.hIcon		= LoadIcon(NULL , IDI_APPLICATION);
25	winc.hCursor		= LoadCursor(NULL , IDC_ARROW);
26	winc.hbrBackground	= (HBRUSH)GetStockObject(WHITE_BRUSH);
27	winc.lpszMenuName	= NULL;
28	winc.lpszClassName	= TEXT("KITTY");
29
30	if (!RegisterClass(&winc)) return 0;
31
32	hwnd = CreateWindow(
33			TEXT("KITTY") , TEXT("Kitty on your lap") ,
34			WS_OVERLAPPEDWINDOW | WS_VISIBLE ,
35			100 , 100 , 200 , 200 , NULL , NULL ,
36			hInstance , NULL
37	);
38
39	if (hwnd == NULL) return 0;
40
41	while (GetMessage(&msg , NULL , 0 , 0)) DispatchMessage(&msg);
42	return msg.wParam;
43}