Use? System;

Namespace? ConsoleApplication 15

{

Class? procedure

{

Static electricity Invalid? Main(string[]？ Parameter)

{

int？ x？ =? null

//? Judge whether it is empty.

What if? (! x.HasValue)

{

Console. WriteLine("x is empty ");

}

x？ =? 100;

//? Judge whether it is valuable.

What if? (x.HasValue)

{

Console. WriteLine(x)；

}

}

}

}