用c语言画一个2次函数图像

#include 
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
PSTR szCmdLine, int iCmdShow)
{
	static TCHAR szAppName[]=TEXT("二次函数");
	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("Error"),
			szAppName, MB_ICONERROR);
		return 0;
	}
	hwnd=CreateWindow(szAppName, TEXT("二次函数"),
		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 int  cxClient, cyClient;
	const static int n=1000;
	HDC         hdc;
	int         i;
	PAINTSTRUCT ps;
	POINT       apt[n];
	switch (message)
	{
	case WM_SIZE:
		cxClient=LOWORD(lParam);
		cyClient=HIWORD(lParam);
		return 0;
	case WM_PAINT:
		hdc=BeginPaint(hwnd, &ps);
		MoveToEx(hdc, 0, cyClient/2, NULL);
		LineTo(hdc, cxClient, cyClient/2);
		MoveToEx(hdc, cxClient/2, 0, NULL);
		LineTo(hdc, cxClient/2, cyClient);
		for (i=0; i < n;++i)
		{
			apt[i].x=cxClient/4+i;	apt[i].y=cyClient-(cyClient/2-i)*(cyClient/2-i)/300-cyClient/2+100;
		}
		Polyline(hdc, apt, n);
		return 0;
	case WM_DESTROY:
		PostQuitMessage(0);
		return 0;
	}
	return DefWindowProc(hwnd, message, wParam, lParam);
}