将hwndButton声明定义为
static HWND hwndButton;

是申明为static HWND hwndButton的;

是编译器说没初始化吗?
应该不会的呀~~
你是如何做的?

我把程序贴出来给你看看吧：
case WM_CREATE:
        GetClientRect(hWnd, &wRect);              // 将程序窗口区域保存到结构变量wRect
        // 建立复选框
        hButtonCi = CreateWindow(TEXT("BUTTON"), TEXT("圆"),
            BS_CHECKBOX | WS_CHILD | WS_VISIBLE,
            wRect.left + 50,
            wRect.bottom - 80,
            75,
            25,
            hWnd,
            (HMENU)0,
            hInst,
            NULL);

        hButtonSq = CreateWindow(TEXT("BUTTON"), TEXT("矩形"),
            BS_CHECKBOX | WS_CHILD | WS_VISIBLE,
            wRect.left + 50,
            wRect.bottom - 40,
            75,
            25,
            hWnd,
            (HMENU)1,
            hInst,
            NULL);
        break;

    case WM_COMMAND:
        if(LOWORD(lParam) == (long)hButtonCi)
        {
            // 读取复选框状态
            nCheck = (WORD)SendMessage(hButtonCi, BM_GETCHECK, 0, 0L);
            if(nCheck == TRUE)
                SendMessage(hButtonCi, BM_SETCHECK, 0, 0L);
            else
                SendMessage(hButtonCi, BM_SETCHECK, 1, 0L);
        }
        else if(LOWORD(lParam) == (long)hButtonSq)
        {
            // 读取复选框状态
            nCheck = (WORD)SendMessage(hButtonSq, BM_GETCHECK, 0, 0L);
            if(nCheck == TRUE)
                SendMessage(hButtonCi, BM_SETCHECK, 0, 0L);
            else
                SendMessage(hButtonSq, BM_SETCHECK, 1, 0L);
        }
        InvalidateRect(hWnd, NULL, TRUE);
        break;

        wmId    = LOWORD(wParam);
        wmEvent = HIWORD(wParam);
        // Parse the menu selections:
        switch (wmId)
        {
        case IDM_ABOUT:
            DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
            break;
        case IDM_EXIT:
            DestroyWindow(hWnd);
            break;
        default:
            return DefWindowProc(hWnd, message, wParam, lParam);
        }
        break;

    case WM_SIZE:
        xc = LOWORD(lParam)/2;
        yc = HIWORD(lParam)/2;

    case WM_PAINT:
        hdc = BeginPaint(hWnd, &ps);
        // TODO: Add any drawing code here...
        //检查复选框以决定是否绘图
        nCheck = (WORD)SendMessage(hButtonCi, BM_GETCHECK, 0, 0L);
        if(nCheck == TRUE)
            Ellipse(hdc, xc - 100, yc - 100, xc + 100 , yc + 100);

        nCheck = (WORD)SendMessage(hButtonSq, BM_GETCHECK, 0, 0L);
        if(nCheck == TRUE)
        {
            MoveToEx(hdc, xc - 100, yc - 100 ,(LPPOINT)NULL);
            LineTo(hdc, xc + 100, yc - 100);
            LineTo(hdc, xc + 100, yc + 100);
            LineTo(hdc, xc - 100, yc + 100);
            LineTo(hdc, xc - 100, yc - 100);
        }

        EndPaint(hWnd, &ps);
        break;
在后面的WM_SIZE中，控件句柄的值根本没有(与前面得到的句柄不一样)，不知道是为什么？

An application should not call BeginPaint except in response to a WM_PAINT message

你不应该在WM_SIZE消息时调用BeginPaint
但应该不是致使原因~~

是编译器说没初始化吗?
你干脆再发完整点的代码,我有时间时给你运行一下看看~~

好呢：完整的程序如下：
// ch8-1.cpp : Defines the entry point for the application.
//

#include "stdafx.h"
#include "ch8-1.h"

#define MAX_LOADSTRING 100
#define mLen    100

// Global Variables:
HINSTANCE hInst;                                // current instance
TCHAR szTitle[MAX_LOADSTRING];                    // The title bar text
TCHAR szWindowClass[MAX_LOADSTRING];            // the main window class name

// Forward declarations of functions included in this code module:
ATOM                MyRegisterClass(HINSTANCE hInstance);
BOOL                InitInstance(HINSTANCE, int);
LRESULT CALLBACK    WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK    About(HWND, UINT, WPARAM, LPARAM);

int APIENTRY _tWinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPTSTR    lpCmdLine,
                     int       nCmdShow)
{
    UNREFERENCED_PARAMETER(hPrevInstance);
    UNREFERENCED_PARAMETER(lpCmdLine);

     // TODO: Place code here.
    MSG msg;
    HACCEL hAccelTable;

    hInst = hInstance;                     // 得到当前程序实例的句柄

    // Initialize global strings
    LoadString(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
    LoadString(hInstance, IDC_CH81, szWindowClass, MAX_LOADSTRING);
    MyRegisterClass(hInstance);

    // Perform application initialization:
    if (!InitInstance (hInstance, nCmdShow))
    {
        return FALSE;
    }

    hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_CH81));

    // Main message loop:
    while (GetMessage(&msg, NULL, 0, 0))
    {
        if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
    }

    return (int) msg.wParam;
}



//
//  FUNCTION: MyRegisterClass()
//
//  PURPOSE: Registers the window class.
//
//  COMMENTS:
//
//    This function and its usage are only necessary if you want this code
//    to be compatible with Win32 systems prior to the 'RegisterClassEx'
//    function that was added to Windows 95. It is important to call this function
//    so that the application will get 'well formed' small icons associated
//    with it.
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{
    WNDCLASSEX wcex;

    wcex.cbSize = sizeof(WNDCLASSEX);

    wcex.style            = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc    = WndProc;
    wcex.cbClsExtra        = 0;
    wcex.cbWndExtra        = 0;
    wcex.hInstance        = hInstance;
    wcex.hIcon            = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_CH81));
    wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground    = (HBRUSH)(COLOR_WINDOW+1);
    wcex.lpszMenuName    = MAKEINTRESOURCE(IDC_CH81);
    wcex.lpszClassName    = szWindowClass;
    wcex.hIconSm        = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));

    return RegisterClassEx(&wcex);
}

//
//   FUNCTION: InitInstance(HINSTANCE, int)
//
//   PURPOSE: Saves instance handle and creates main window
//
//   COMMENTS:
//
//        In this function, we save the instance handle in a global variable and
//        create and display the main program window.
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
   HWND hWnd;

   hInst = hInstance; // Store instance handle in our global variable

   hWnd = CreateWindow(szWindowClass, TEXT("编辑框设计"), WS_OVERLAPPEDWINDOW,
      CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hInstance, NULL);

   if (!hWnd)
   {
      return FALSE;
   }

   ShowWindow(hWnd, nCmdShow);
   UpdateWindow(hWnd);

   return TRUE;
}

//
//  FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  PURPOSE:  Processes messages for the main window.
//
//  WM_COMMAND    - process the application menu
//  WM_PAINT    - Paint the main window
//  WM_DESTROY    - post a quit message and return
//
//

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    int wmId, wmEvent;
    PAINTSTRUCT ps;
    HDC hdc;

    // 定义函数变量
    static HWND hButtonExt;               // 结束按钮句柄
    static HWND hButtonCls;               // 清除按钮句柄
    static HWND hEditSou;                    // 编辑控件窗口句柄
    static HWND hEditDst;

    RECT        wRect;                    // 窗口区域
    static int x, y, bWidth, bHeight;
    wchar_t txtBuffer[mLen];

    // 初始化变量
    bWidth = 50;
    bHeight = 30;

    switch (message)
    {
    case WM_CREATE:
        GetClientRect(hWnd, &wRect);
        x = (wRect.right - bWidth)*2/5;                   //按钮的x位置
        y = (wRect.bottom - bHeight)*5/6;                 //按钮的y位置

        // 建立结束按钮 窗口ID为0
        hButtonExt = CreateWindow(TEXT("button"), TEXT("结束"), WS_CHILD | WS_VISIBLE | BS_DEFPUSHBUTTON,
            x, y, bWidth, bHeight, hWnd, (HMENU)0,
            hInst, NULL);

        x = (wRect.right - bWidth)*3/5;                   //按钮的x位置
        y = (wRect.bottom - bHeight)*5/6;                 //按钮的y位置

        // 建立清除按钮 窗口ID为1
        hButtonCls = CreateWindow(TEXT("BUTTON"), TEXT("清除"), WS_CHILD | WS_VISIBLE | BS_DEFPUSHBUTTON,
            x, y, bWidth, bHeight, hWnd, (HMENU)1,
            hInst, NULL);

        
        // 建立源编辑控件 窗口ID为2
        hEditSou = CreateWindow(TEXT("edit"), NULL, 
            WS_CHILD | WS_VISIBLE |ES_MULTILINE | WS_BORDER| WS_VSCROLL | ES_AUTOVSCROLL,
            20, 20, wRect.right - 40, 50,
            hWnd, (HMENU)2,
            hInst, NULL);

        

// 建立目的编辑控件 窗口ID为3
        hEditDst = CreateWindow(TEXT("edit"), NULL, 
            WS_CHILD | WS_VISIBLE |ES_MULTILINE | WS_BORDER| WS_VSCROLL | ES_AUTOVSCROLL,
            20, 120, wRect.right - 40,50,
            hWnd, (HMENU)3,
            hInst, NULL);
        break;

    case WM_COMMAND:
        wmId    = LOWORD(wParam);
        wmEvent = HIWORD(wParam);
        // Parse the menu selections:
        if(LOWORD(lParam) == (LPARAM)hButtonExt)                   // 看是否按结束按钮
            PostQuitMessage(0);                                 //程序结束
        else if (LOWORD(lParam) == (LPARAM)hButtonCls)
        {
            GetWindowText(hEditSou, (LPWSTR)txtBuffer, mLen);           //得到源编辑窗口中的字符
            //SetWindowText(hEditDst, (LPWSTR)txtBuffer);                 // 将字符数组的数据写入目的编辑窗口
            hdc = GetDC(hWnd);
            // 在主窗口输出字符串
            TextOut(hdc, 100, 250, txtBuffer, lstrlen(txtBuffer));
            ReleaseDC(hWnd, hdc);
            // 如果是密码检测，程序代码为：
            // hdc = GetDC(hWnd);
            // GetWindowText(hEditSou, (LPWSTR)txtBuffer, mLen);    // 获取编辑框中的字符
            // if (!strcmp(txtBuffer, "qouling")                    // 与预定义的密码比较
            //TextOut(hdc, 100, 250, "欢迎使用本系统", 14);
            // else
            // TextOut(hdc, 100, 250, "密码错误", 8);

            ReleaseDC(hWnd, hdc);
        }
        
        switch (wmId)
        {
        case IDM_ABOUT:
            DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
            break;
        case IDM_EXIT:
            DestroyWindow(hWnd);
            break;
        default:
            return DefWindowProc(hWnd, message, wParam, lParam);
        }
        break;

    case WM_PAINT:
        hdc = BeginPaint(hWnd, &ps);
        // TODO: Add any drawing code here...
        EndPaint(hWnd, &ps);
        break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;
}

// Message handler for about box.
INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
    UNREFERENCED_PARAMETER(lParam);
    switch (message)
    {
    case WM_INITDIALOG:
        return (INT_PTR)TRUE;

    case WM_COMMAND:
        if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL)
        {
            EndDialog(hDlg, LOWORD(wParam));
            return (INT_PTR)TRUE;
        }
        break;
    }
    return (INT_PTR)FALSE;
}

[quote]       
        if(LOWORD(lParam) == (LPARAM)hButtonExt)                   // 看是否按结束按钮
            PostQuitMessage(0);                                 //程序结束
        else if (LOWORD(lParam) == (LPARAM)hButtonCls)
 [/quote]

改成这样就行了,并没有你说的 "没有初始化"
       if((HWND)lParam == hButtonExt)      
            PostQuitMessage(0);                  
        else if ((HWND)lParam == hButtonCls)

如果WM_COMMAND来自控件,则lParam是控件句柄,LOWORD(lParam)什么都不是

非常感谢，你帮我解决一个制约我学习的大问题，还有一个程序，不知哥们可不可以帮我再看一看？