Visual C++ .NET/Statement/using

using directive

 
#include "stdafx.h"
#using "System.Windows.Forms.dll"
using namespace System::Windows::Forms;
int main()
{
   MessageBox::Show("Hello World!");
}

using dll

 
#include "stdafx.h"
#using "System.Windows.Forms.dll"
int main()
{
   System::Windows::Forms::MessageBox::Show("Hello World!");
}