visual programming - c++

Question

sir i have written a simple program to display a message box in visual c++ 2008 but the problem is that when i run this code a dialog box shows that "your project is out of date would you like to build it"
when i press yes it shows error
so what is the problem???
the code is here
#include <Windows.h> /* The standard "windows.h" inclusion */
int WINAPI WinMain( HINSTANCE hInstance, /* A handle to the current instance of the application. */
HINSTANCE hPrevInstance, /* A handle to the previous instance of the application. */
LPSTR lpCmdLine, /* The command line for the application, excluding the program name. */
int nCmdShow) /* Controls how the window is to be shown. */
{
/* Call to the MessageBox function */
MessageBox(NULL, "Hello, Windows API!", "Hello", MB_OK);
/* WinMain returns 0 if we exit before we enter message loop, more on that to come */
return 0;
}
Whenever i run this in visuall c++ 2008 it says project out of date, do u want to build so i click yes but then it cant
down the bottom it says
1>Linking...
1>MSVCRTD.lib(crtexe.obj) : error LNK2001: unresolved external symbol _main
1>C:\Documents and Settings**\My Documents\Visual Studio 2008\Projects\msg\Debug\msg.exe : fatal error LNK1120: 1 unresolved externals
1>Build log was saved at "file://c:\Documents and Settings**\My Documents\Visual Studio 2008\Projects\msg\msg\Debug\BuildLog.htm"
1>Wrath Lands - 2 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Answer 1

VS creates UNICODE projects by default so macros like MessageBox evaluates to MessageBoxW which expects LPCWSTR arguments and not LPCSTR. Try change to: MessageBox(NULL, _T("Hello, Windows API!"), _T("Hello"), MB_OK);

Answer 2

The error message error LNK2001: unresolved external symbol _main is important. It looks like you've created a console project but there is no main() function defined, hence the linker error.
When you create a new Visual Studio project as a Win32 Console Application it assumes the entry point to your program will be the normal C/C++ main() function and it links with the C/C++ library startup code. If you instead create a Win32 Project it assumes the entry point will be WinMain() and links with Windows application startup code.
To avoid this problem you should begin with a Win32 Project. To fix it after the fact you could try going into Project Properties -> Linker -> System and change the SubSystem option from Console (/SUBSYSTEM:CONSOLE) to Windows (/SUBSYSTEM:WINDOWS). Note that there may be other settings that should be changed as well so I suggest you just start fresh with a new Win32 Project instead.