【C#】INT,DOUBLE,BOOL 宣告成NULL值

  Nullable   x1 = null;
  Nullable   x2 = null;
  Nullable   x3 = null;
//或

//test
            if (x1.HasValue)
            {
                
                Response.Write(x1.ToString());
            }
            else
            {
                x1 = 1;
                Response.Write(x1.ToString());
            }