关于画笔的一点问题，跟大家讨论讨论，欢迎交流。

目的：我想让25个矩形用默认黑色画笔，而让中间的差号用红色
第一种情况：
hpen=CreatePen(PS_SOLID,2,RGB(255,0,0));
SelectObject(hdc,hpen);
DeleteObject(hpen);
SelectObject(hdc,GetStockObject(BLACK_PEN));
理论上并没有发现问题，建一个画笔，选进DC，然后画线，之后删除此画笔，再把黑色画笔选进去DC，为什么就没达到效果呢？
代码：

#include <windows.h>

#define DIVISIONS 5

LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,

                    PSTR szCmdLine, int iCmdShow)

{

     static TCHAR szAppName [] = TEXT ("RECT") ;

     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  = NULL;

     wndclass.lpszClassName = szAppName ;

     

     if (!RegisterClass (&wndclass))

     {

          MessageBox (NULL, TEXT ("This program requires Windows NT!"),

                      szAppName, MB_ICONERROR) ;

          return 0 ;

     }

     

     hwnd = CreateWindow (szAppName, TEXT ("RECT TEST"), 

                          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 ;

}

     static int     cxClient, cyClient;

         static BOOL state[DIVISIONS][DIVISIONS];

LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)

{



     HDC            hdc;

         HPEN hpen;

     PAINTSTRUCT    ps ;

         RECT     rect;

         int i,j;

         int x,y;



         TCHAR szAppName[]="RECTANGLE";

     

     switch (message)

     {

     case WM_CREATE:



          return 0 ;





     case WM_SIZE:

          cxClient = LOWORD (lParam)/DIVISIONS ;

          cyClient = HIWORD (lParam)/DIVISIONS ;

          return 0 ;

         case WM_LBUTTONDOWN:

                        x=LOWORD(lParam);

                        y=HIWORD(lParam);

                        i=j=0;

                        while(!(x<i*cxClient))

                        {

                                ++i;

                        }

                        while(!(y<j*cyClient))

                        {

                                ++j;

                        }

                        if(state[i-1][j-1]==TRUE)

                        {

                                state[i-1][j-1]=FALSE;

                        }

                        else

                        {

                                state[i-1][j-1]=TRUE;

                        }

                        InvalidateRect(hwnd,NULL,TRUE);

                        return 0;

     case WM_PAINT:

                 hdc=BeginPaint(hwnd,&ps);

                 GetClientRect(hwnd,&rect);

                 hpen=CreatePen(PS_SOLID,2,RGB(255,0,0));

                

                for(j=0;j<DIVISIONS;j++)

                        for(i=0;i<DIVISIONS;i++)

                        {

                                Rectangle(hdc,i*cxClient,j*cyClient,(i+1)*cxClient,(j+1)*cyClient);

                                if(state[i][j])

                                {

                                         SelectObject(hdc,hpen);

                                        MoveToEx(hdc,i*cxClient,j*cyClient,NULL);

                                        LineTo(hdc,(i+1)*cxClient,(j+1)*cyClient);

                                                MoveToEx(hdc,i*cxClient,(j+1)*cyClient,NULL);

                                        LineTo(hdc,(i+1)*cxClient,j*cyClient);

                                        DeleteObject(hpen);

                                        SelectObject(hdc,GetStockObject(BLACK_PEN));

                                                 

                                }

                        }

                 EndPaint(hwnd,&ps);



          return 0 ;



     case WM_DESTROY:

        

          PostQuitMessage (0) ;

          return 0 ;

     }

     return DefWindowProc (hwnd, message, wParam, lParam) ;

}

情况2
如果换成下面这样：

 if(state[i][j])



                                {



                                         hpen=(HPEN)SelectObject(hdc,CreatePen(PS_SOLID,2,RGB(255,0,0)));



                                        MoveToEx(hdc,i*cxClient,j*cyClient,NULL);



                                        LineTo(hdc,(i+1)*cxClient,(j+1)*cyClient);



                                                MoveToEx(hdc,i*cxClient,(j+1)*cyClient,NULL);



                                        LineTo(hdc,(i+1)*cxClient,j*cyClient);



                                        DeleteObject(SelectObject(hdc,hpen));



                                        //SelectObject(hdc,GetStockObject(BLACK_PEN));



                                                 



                                }

倒是就没问题了。但是始终没发现情况1中为什么不可以满足要求？3Q!