C语言_SDK_复选框，我这个代码怎么会错呢？

对话框：

代码：

#include "stdafx.h"
#include <windows.h>
#include <windowsx.h>
#include "resource.h"
#include "MainDlg.h"
BOOL WINAPI Main_Proc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch(uMsg)
    {
        HANDLE_MSG(hWnd, WM_INITDIALOG, Main_OnInitDialog);
        HANDLE_MSG(hWnd, WM_COMMAND, Main_OnCommand);
  HANDLE_MSG(hWnd,WM_CLOSE, Main_OnClose);
    }

    return FALSE;
}

BOOL Main_OnInitDialog(HWND hwnd, HWND hwndFocus, LPARAM lParam)
{
    return TRUE;
}

void Main_OnCommand(HWND hwnd, int id, HWND hwndCtl, UINT codeNotify)
{
    switch(id)
    {
        case IDC_SET:
  {
   HWND hwnd_check = GetDlgItem(hwnd,IDC_CHECK1);
   int check_state = Button_GetCheck(hwnd_check);
   if(BST_UNCHECKED==check_state)
   {
    Button_SetCheck(hwnd_check,BST_CHECKED);
   }
   if(BST_CHECKED==check_state)
   {
    Button_SetCheck(hwnd_check,BST_UNCHECKED);
   }
  }
  break;
  case IDC_OK:
  {
   HWND hwnd_check = GetDlgItem(hwnd,IDC_CHECK1);
   int check_state = Button_GetCheck(hwnd_check);
   if(BST_UNCHECKED==check_state)
   {
    MessageBox(hwnd,TEXT("未选中"),TEXT(""),MB_OK);
   }
   if(BST_CHECKED==check_state)
   {
    MessageBox(hwnd,TEXT("已选中"),TEXT(""),MB_OK);
   }
        break;
        default:
  break;
    }
}

void Main_OnClose(HWND hwnd)
{
    EndDialog(hwnd, 0);
}

//这个我认为不会错啊，可是.....

//我写完第一个case是调试了一下没错，

//可是再写第二个case是就错了，

//怎么了？变量名不能相同？好像不是这个问题！