新手学习windows编程，遇到有关问题了，求教

新手学习windows编程，遇到问题了，求教！
不知道为什么，没有出现窗口。。。

C/C++ code

#include <windows.h>LRESULT CALLBACK WindowProc(  HWND hwnd,      // handle to window  UINT uMsg,      // message identifier  WPARAM wParam,  // first message parameter  LPARAM lParam   // second message parameter);int WINAPI WinMain(  HINSTANCE hInstance,      // handle to current instance  HINSTANCE hPrevInstance,  // handle to previous instance  LPSTR lpCmdLine,          // command line  int nCmdShow              // show state){    WNDCLASS wndclass;    wndclass.cbClsExtra=0;    wndclass.cbWndExtra=0;    wndclass.hbrBackground=(HBRUSH) GetStockObject (WHITE_BRUSH);    wndclass.hCursor=NULL;    wndclass.hIcon=NULL;    wndclass.hInstance=hInstance;    wndclass.lpfnWndProc=WindowProc;    wndclass.lpszClassName="my first";    wndclass.style=CS_VREDRAW | CS_HREDRAW;    wndclass.lpszMenuName=NULL;    RegisterClass(&wndclass);    HWND hwnd=CreateWindow(                              "my first",  // registered class name                              NULL, // window name                              WS_BORDER,        // window style                              0,                // horizontal position of window                              0,                // vertical position of window                              20,           // window width                              20,          // window height                              NULL,      // handle to parent or owner window                              NULL,          // menu handle or child identifier                              hInstance,  // handle to application instance                              NULL       // window-creation data                            );    ShowWindow(    hwnd,     // handle to window    SW_MAXIMIZE   // show state              );    UpdateWindow(    hwnd   // handle to window    );    MSG msg;    while(GetMessage(                      &msg,         // message information                      hwnd,           // handle to window                      NULL,  // first message                      NULL  // last message                    )                    )    {        TranslateMessage (&msg) ;        DispatchMessage (&msg) ;    }    return 0;}LRESULT CALLBACK WindowProc(  HWND hwnd,      // handle to window  UINT uMsg,      // message identifier  WPARAM wParam,  // first message parameter  LPARAM lParam   // second message parameter){    switch(uMsg)    {    case WM_LBUTTONDOWN:        MessageBox(                  hwnd,          // handle to owner window                  "lbuttondown",     // text in message box                  "zhq message box title",  // message box title                  MB_OK          // message box style                );        return 0;    case WM_DESTROY:        PostQuitMessage (0) ;        return 0;    }    return 0;}

C/C++ code

default: //执行默认的消息处理        return(DefWindowProc(hwnd,uMsg,wParam,lParam));