vc API编写计算器出现问题

#include<windows.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include<string.h>
#define IDE_RESULT                      101
#define IDB_NUM0                        110
#define IDB_NUM1                        111
#define IDB_NUM2                        112
#define IDB_NUM3                        113
#define IDB_NUM4                        114
#define IDB_NUM5                        115
#define IDB_NUM6                        116
#define IDB_NUM7                        117
#define IDB_NUM8                        118
#define IDB_NUM9                        119
#define IDB_NUMDEC                      120
#define IDB_ADD                         121
#define IDB_SUB                         122
#define IDB_MUL                         123
#define IDB_DIV                         124
#define IDB_EQU                         127
#define IDB_CE                          129
 #ifdef APSTUDIO_INVOKED
#ifndef APSTUDIO_READONLY_SYMBOLS
#define _APS_NEXT_RESOURCE_VALUE        104
#define _APS_NEXT_COMMAND_VALUE         40001
#define _APS_NEXT_CONTROL_VALUE         1000
#define _APS_NEXT_SYMED_VALUE           101
#endif
#endif
 HWND hWnd,
     hEditResult,//编辑框；
     hButton0,hButton1,hButton2,hButton3,
 hButton4,hButton5,hButton6,hButton7,
 hButton8,hButton9,hButtonDec, 
     hButtonAdd,hButtonSub,hButtonMul,hButtonDiv,   
     hButtonEqu,
 hButtonCE;
 
HINSTANCE hInst;
char lpszAddItem[20]="";
char lpszResult[20]="";
char lpszResult1[20]="";
char lpszResult2[20]="";
char lpszOpt[]="N"; 
char *stop;
double nAddItem=0,nResult=0;
double nResult1=0,nResult2=0;
int nMax;
int nOptF=0; 
bool bDec=false; LRESULT CALLBACK WndProc(HWND,UINT,WPARAM,LPARAM);
void EquResult(); 
void NumResult(char *NumData); 
int WINAPI WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
{
 
HWND hWnd;
    MSG Message;
WNDCLASS WndClass;
char lpszClassName[]="编辑框";
char lpszTitle[]="计算器";
WndClass.cbClsExtra=0;
WndClass.cbWndExtra=0;
WndClass.hbrBackground=(HBRUSH)(GetStockObject(WHITE_BRUSH));
    WndClass.hCursor=LoadCursor(NULL,IDC_ARROW);
WndClass.hIcon=LoadIcon(NULL,"WinIcon");
WndClass.hInstance=hInstance;
WndClass.lpfnWndProc=WndProc; 
WndClass.lpszClassName=lpszClassName;
    WndClass.lpszMenuName="Menu";
WndClass.style=0;
    if(!RegisterClass(&WndClass))
{
MessageBeep(0);
return FALSE;
}   hInst=hInstance;
   hWnd=CreateWindow(
               lpszClassName,
               lpszTitle,
   WS_OVERLAPPED | WS_SYSMENU | WS_MINIMIZEBOX,
   CW_USEDEFAULT,
   CW_USEDEFAULT,
   210,230,
   NULL,
   NULL,
   hInstance,
   NULL
  );
    ShowWindow(hWnd,nCmdShow);
    UpdateWindow(hWnd);

while(GetMessage(&Message,NULL,0,0))
{
    TranslateMessage(&Message);
    DispatchMessage(&Message);
}
return Message.wParam;
}LRESULT CALLBACK WndProc(HWND hwnd,
 UINT message,
 WPARAM wParam,
 LPARAM lParam)
{
switch(message)
{
case WM_CREATE:
        hEditResult=CreateWindow("EDIT",       //建立文本框
                    NULL,
WS_CHILD | WS_VISIBLE | ES_RIGHT | WS_BORDER | ES_READONLY,
10,10,
185,24,
hwnd,
(HMENU)IDE_RESULT,
hInst,
NULL);
hButton7=CreateWindow("BUTTON",  //建立按钮7
                    "7",
WS_CHILD | WS_VISIBLE,
10,40,
30,30,
hwnd,
(HMENU) IDB_NUM7,
hInst,
NULL);


SetWindowText(hEditResult,"0");
break;
case WM_SETFOCUS:
SetFocus(hEditResult);
break;

case WM_COMMAND:
   switch(LOWORD(wParam))
   {
    // 零至玖与点按钮
              case IDB_NUM0:
   if (nOptF==0)
   break;
    NumResult("0");
break;
                case IDB_NUM1: 
   NumResult("1");
break;
  case IDB_NUM2:
    NumResult("2");     
    break;
                  case IDB_NUM3:
    NumResult("3");     
    break;
                  case IDB_NUM4:
    NumResult("4");
    break;
                  case IDB_NUM5:
    NumResult("5");
    break;
                  case IDB_NUM6:
    NumResult("6");
    break;
                  case IDB_NUM7:
    NumResult("7");
    break;
      case IDB_NUM8:
    NumResult("8");
    break;
                  case IDB_NUM9:
    NumResult("9");
    break;
                  case IDB_NUMDEC:
if (bDec==true) 
break;  //如果已按了点号就返回
                        NumResult(".");
                        nOptF=1;      //按了操作符键
bDec=true;    //按了点操作符;
break;
                  
        
        break; 
// 加,减,乘,除
          case IDB_ADD:
                        EquResult();
strcpy(lpszOpt,"+");     //设置按了操作符号+
    break;
  case IDB_SUB:     
    EquResult();
strcpy(lpszOpt,"-");
    break;
  case IDB_MUL: 
EquResult();
strcpy(lpszOpt,"*");  
    break;
  case IDB_DIV:  
    EquResult();
strcpy(lpszOpt,"/");
    break;
     
  case IDB_EQU:
    //算出等于结果
    EquResult();
strcpy(lpszOpt,"N");
    break;
   
  case IDB_CE:
  SetWindowText(hEditResult,"0");
      nResult=0;
      nAddItem=0;
  nResult1=0;
  nResult2=0;
  strcpy(lpszResult1,"0");
                      strcpy(lpszResult2,"0");
  nOptF=0;
  bDec=false;
  strcpy(lpszOpt,"N");  //贮存操作符号
  break;

   }
   break;
   case WM_DESTROY:
    PostQuitMessage(0);
    break;
    default:
    return DefWindowProc(hwnd,message,wParam,lParam);
}
return 0;
}//-----------------------按下操作符(+,-,*,/,=)处理函数-----------------------
void EquResult()
{

 //算出结果
    if (strcmp(lpszOpt,"N")==0)
{
nResult1=strtod(lpszResult1,&stop);
}
else
{
switch(*lpszOpt)    //比较上一次按的操作符后所得的结果
{
case '+':
nResult1=strtod(lpszResult1,&stop);
nResult2=strtod(lpszResult2,&stop);
nResult1=nResult1+nResult2;
break;
case '-':
nResult1=strtod(lpszResult1,&stop);
nResult2=strtod(lpszResult2,&stop);
nResult1=nResult1-nResult2;
break;
case '*':
nResult1=strtod(lpszResult1,&stop);
nResult2=strtod(lpszResult2,&stop);
nResult1=nResult1*nResult2;
break;
case '/':
nResult1=strtod(lpszResult1,&stop);
nResult2=strtod(lpszResult2,&stop);
if (nResult2==0)
{
   MessageBox(hWnd,"除数不能为零!","功能",MB_OK);
   break;
}
nResult1=nResult1/nResult2;
break;


}

}
                        nResult1=nResult1*1.0;
    _gcvt(nResult1,15,lpszResult1); //双精度转化为字符串
    SetWindowText(hEditResult,lpszResult1);
nOptF=0;
bDec=false; 
}//按下数字键(0~9和小数点)的操作处理函数
void NumResult(char *NumData)
{

    if (nOptF==0)
    SetWindowText(hEditResult,"");
    nMax=GetWindowTextLength(hEditResult)+1;
     GetWindowText(hEditResult,lpszAddItem,nMax);
     strcat(lpszAddItem,NumData);        ///字符串加该数字键的字符
    if (strcmp(lpszOpt,"N")==0)
{
strcpy(lpszResult1,lpszAddItem);
        SetWindowText(hEditResult,lpszResult1);
}
else
{
strcpy(lpszResult2,lpszAddItem);
         SetWindowText(hEditResult,lpszResult2);
}
                        nOptF=1;  //按下了数字键
}
inking...
LIBCD.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
Debug/JISUANQI.exe : fatal error LNK1120: 1 unresolved externals
执行 link.exe 时出错.JISUANQI.exe - 1 error(s), 0 warning
怎么解决啊  
急APIVC