请帮我调试一个程序（显示两个窗口）

// DEMO2_5.CPP - Creates two windows based on the same
// window class

// INCLUDES ///////////////////////////////////////////////
#define WIN32_LEAN_AND_MEAN // just say no to MFC

#include <windows.h> // include all the windows headers
#include <windowsx.h> // include useful macros
#include <stdio.h>
#include <math.h>

// DEFINES ////////////////////////////////////////////////

// defines for windows
#define WINDOW_CLASS_NAME "WINCLASS1"

// GLOBALS ////////////////////////////////////////////////


// FUNCTIONS //////////////////////////////////////////////
LRESULT CALLBACK WindowProc(HWND hwnd,
UINT msg,
WPARAM wparam,
LPARAM lparam)
{
// this is the main message handler of the system
PAINTSTRUCT ps; // used in WM_PAINT
HDC hdc; // handle to a device context

// what is the message
switch(msg)
{
case WM_CREATE:
{
// do initialization stuff here

// return success
return(0);
} break;

case WM_PAINT:
{
// simply validate the window
hdc = BeginPaint(hwnd,&ps);
// you would do all your painting here
EndPaint(hwnd,&ps);

// return success
return(0);
} break;

case WM_DESTROY:
{
// kill the application, this sends a WM_QUIT message
PostQuitMessage(0);

// return success
return(0);
} break;

default:break;

} // end switch

// process any messages that we didn't take care of
return (DefWindowProc(hwnd, msg, wparam, lparam));

} // end WinProc

// WINMAIN ////////////////////////////////////////////////
int WINAPI WinMain( HINSTANCE hinstance,
HINSTANCE hprevinstance,
LPSTR lpcmdline,
int ncmdshow)
{

WNDCLASSEX winclass; // this will hold the class we create
HWND hwnd; // generic window handle
MSG msg; // generic message

// first fill in the window class stucture
winclass.cbSize = sizeof(WNDCLASSEX);
winclass.style = CS_DBLCLKS | CS_OWNDC |
CS_HREDRAW | CS_VREDRAW;
winclass.lpfnWndProc = WindowProc;
winclass.cbClsExtra = 0;
winclass.cbWndExtra = 0;
winclass.hInstance = hinstance;
winclass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
winclass.hCursor = LoadCursor(NULL, IDC_ARROW);
winclass.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH);
winclass.lpszMenuName = NULL;
winclass.lpszClassName = WINDOW_CLASS_NAME;
winclass.hIconSm = LoadIcon(NULL, IDI_APPLICATION);

WNDCLASSEX winclass2; // this will hold the class we create
HWND hwnd2; // generic window handle
MSG msg2; // generic message

// first fill in the window class stucture
winclass2.cbSize = sizeof(WNDCLASSEX);
winclass2.style = CS_DBLCLKS | CS_OWNDC |
CS_HREDRAW | CS_VREDRAW;
winclass2.lpfnWndProc = WindowProc;
winclass2.cbClsExtra = 0;
winclass2.cbWndExtra = 0;
winclass2.hInstance = hinstance;
winclass2.hIcon = LoadIcon(NULL, IDI_APPLICATION);
winclass2.hCursor = LoadCursor(NULL, IDC_ARROW);
winclass2.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH);
winclass2.lpszMenuName = NULL;
winclass2.lpszClassName = WINDOW_CLASS_NAME;
winclass2.hIconSm = LoadIcon(NULL, IDI_APPLICATION);

// register the window class
if (!RegisterClassEx(&winclass))
return(0);

// create the first window
if (!(hwnd = CreateWindowEx(NULL, // extended style
WINDOW_CLASS_NAME, // class
"Window 1 Based on WINCLASS1", // title
WS_OVERLAPPEDWINDOW | WS_VISIBLE,
0,0, // initial x,y
400,400, // initial width, height
NULL, // handle to parent
NULL, // handle to menu
hinstance,// instance of this application
NULL))) // extra creation parms
return(0);

// create the second window
if (!(hwnd2 = CreateWindowEx(NULL, // extended style
WINDOW_CLASS_NAME, // class
"Window 2 Also Based on WINCLASS1", // title
WS_OVERLAPPEDWINDOW | WS_VISIBLE,
100,100, // initial x,y
400,400, // initial width, height
NULL, // handle to parent
NULL, // handle to menu
hinstance,// instance of this application
NULL))) // extra creation parms
return(0);

// enter main event loop, but this time we use PeekMessage()
// instead of GetMessage() to retrieve messages
while(TRUE)
{
// test if there is a message in queue, if so get it
if (PeekMessage(&msg,NULL,0,0,PM_REMOVE)&&
PeekMessage(&msg2,NULL,0,0,PM_REMOVE))
{
// test if this is a quit
if (msg.message && msg2.message == WM_QUIT)
break;

// translate any accelerator keys
TranslateMessage(&msg);

// send the message to the window proc
DispatchMessage(&msg);
} // end if

// main game processing goes here

} // end while

// return to Windows like this
return(msg.wParam);

} // end WinMain

///////////////////////////////////////////////////////////



Linking...
LIBCD.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
Debug/Demo2_5.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.

Demo2_5.exe - 2 error(s), 0 warning(s)
问题1：遇到上面的编译错误怎么办？
问题2：还有当关闭两个窗口中的任意一个，另一个也随之关闭
应用程序就此结束运行，怎么才能可以一次仅关掉一个窗口？
两个都关掉应用程序才结束运行。