帮我看一下，单步调试时不能显示界面，什么原因，急急急

帮我看一下，单步调试时不能显示界面，什么原因
#include <windows.h>
#include <stdio.h>LRESULT CALLBACK WinSunProc(
  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 wndcls;
wndcls.cbClsExtra=0;
wndcls.cbWndExtra=0;
wndcls.hbrBackground=(HBRUSH)GetStockObject(BLACK_BRUSH);
wndcls.hCursor=LoadCursor(NULL,IDC_CROSS);
wndcls.hIcon=LoadIcon(NULL,IDI_ERROR);
wndcls.hInstance=hInstance;
wndcls.lpfnWndProc=WinSunProc;
wndcls.lpszClassName="sunxin2006";
wndcls.lpszMenuName=NULL;
wndcls.style=CS_HREDRAW | CS_VREDRAW;
RegisterClass(&wndcls); HWND hwnd;
hwnd=CreateWindow("sunxin2006","http://www.sunxin.org",WS_OVERLAPPEDWINDOW,
0,0,600,400,NULL,NULL,hInstance,NULL); ShowWindow(hwnd,SW_SHOWNORMAL);
UpdateWindow(hwnd); MSG msg;
while(GetMessage(&msg,NULL,0,0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return msg.wParam;
}LRESULT CALLBACK WinSunProc(
  HWND hwnd,      // handle to window
  UINT uMsg,      // message identifier
  WPARAM wParam,  // first message parameter
  LPARAM lParam   // second message parameter
)
{
switch(uMsg)
{
case WM_CHAR:
char szChar[20];
sprintf(szChar,"char code is %d",wParam);
MessageBox(hwnd,szChar,"char",0);
break;
case WM_LBUTTONDOWN:
MessageBox(hwnd,"mouse clicked","message",0);
HDC hdc;
hdc=GetDC(hwnd);
TextOut(hdc,0,50,"程序员之家",strlen("程序员之家"));
//ReleaseDC(hwnd,hdc);
break;
case WM_PAINT:
HDC hDC;
PAINTSTRUCT ps;
hDC=BeginPaint(hwnd,&ps);
TextOut(hDC,0,0,"http://www.sunxin.org",strlen("http://www.sunxin.org"));
EndPaint(hwnd,&ps);
break;
case WM_CLOSE:
if(IDYES==MessageBox(hwnd,"是否真的结束？","message",MB_YESNO))
{
DestroyWindow(hwnd);
}
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hwnd,uMsg,wParam,lParam);
}
return 0;
}