Why this simple code is giving syntax error?

#include <iostream>
using namespace std;


void fun(int i)
{
    cout<<"Called with int "<<i;
}

void main()
{
    using df = decltype(&fun);
}

I am getting following syntax errors in Visual Studio,

Error   1   error C2143: syntax error : missing ';' before '='  c:\users\kpranit\documents\visual studio 2012\projects\sample\sample\sample.cpp 12

Error   2   error C2873: 'df' : symbol cannot be used in a using-declaration    c:\users\kpranit\documents\visual studio 2012\projects\sample\sample\sample.cpp 12