Unhandled exception in 按钮.exe: 0xC0000005: Access Violation - C++ Builder / Windows SDK/API

#include<windows.h>
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
TCHAR szAppName[]=TEXT("按钮");
int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,PSTR szCmdLine,int iCmdShow)
{
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 = szAppName ;
wndclass.lpszClassName = szAppName ;
if (!RegisterClass (&wndclass))
{
MessageBox (NULL, TEXT ("This program requires Windows NT!"),
szAppName, MB_ICONERROR) ;
return 0 ;
}

hwnd = CreateWindow (szAppName, TEXT ("Menu Demonstration"),
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)
{
TEXTMETRIC tm;
HWND hwnda;
static int cxChar,cyChar;
switch(message)
{
case WM_CREATE:
{

HDC hdc = GetDC (hwnd) ;
GetTextMetrics (hdc, &tm) ;
cxChar = tm.tmAveCharWidth ;
cyChar = tm.tmHeight + tm.tmExternalLeading ;
ReleaseDC (hwnd, hdc) ;
hwnda= CreateWindow ("button", "确定",
WS_CHILD | WS_VISIBLE|BS_AUTO3STATE,
0, 0,
cxChar*10, cyChar*5,
hwnd, (HMENU)1,
((LPCREATESTRUCT) lParam) -> hInstance, NULL) ;
}break;
case WM_SIZE:
{

}break;
case WM_COMMAND:
{
switch(LOWORD(wParam))
{
case 1:
int i=(int)SendMessage(hwnda,BM_GETCHECK,0,0);
TCHAR *i1;
itoa(i,i1,10);
MessageBox(hwnd,i1,TEXT(""),MB_OK);break;
}
}break;
case WM_DESTROY :
PostQuitMessage (0) ;
break;
}
return DefWindowProc (hwnd, message, wParam, lParam) ;
}

不要看以上那么复杂的代码，关键是一下这句------
case 1:
int i=(int)SendMessage(hwnda,BM_GETCHECK,0,0);
TCHAR *i1;
itoa(i,i1,10);
MessageBox(hwnd,i1,TEXT(""),MB_OK);break;
我企图返回BS_AUTO3STATE这个控制的状态按不知为何抛出了以上异常？
高手帮忙。

[解决办法]
i1没分配内存
TCHAR i1[32];