#include "stdafx.h"
#include <windows.h>
#include <windowsx.h>
#include "resource.h"
#include "MainDlg.h"
#include <stdlib.h>
#include <string.h>

TCHAR Num[256];

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_BUT0:
            ShowNumber(hwnd,0);
            break;
        case IDC_BUT1:
               ShowNumber(hwnd,1);
               break;
       case IDC_BUT2:
              ShowNumber(hwnd,2);

              break;
       case IDC_BUT3:

             ShowNumber(hwnd,3);

             break;
       case IDC_BUT4:

              ShowNumber(hwnd,4);

              break;
      case IDC_BUT5:

            ShowNumber(hwnd,5);

            break;
     case IDC_BUT6:

           ShowNumber(hwnd,6);

           break;
     case IDC_BUT7:

           ShowNumber(hwnd,7);

           break;
   case IDC_BUT8:

          ShowNumber(hwnd,8);

          break;
 case IDC_BUT9:

        ShowNumber(hwnd,9);

         break;
 default:

 break;
    }
}
void ShowNumber(HWND hwnd,int i)
{
TCHAR iNum[256];
itoa(i,iNum,10);
strcat(Num,iNum);
    SetDlgItemText(hwnd,IDC_EDIT,Num);
}

void Main_OnClose(HWND hwnd)
{
    EndDialog(hwnd, 0);
}
error C2065: 'ShowNumber' : undeclared identifier

error C2373: 'ShowNumber' : redefinition; different type modifiers

已经解决了，忘了在头文件里加函数声明了。