Question

I am trying to use autoimplemented properties.
It shows me error

    public OpenMode OpenFor
    {
        get;//must declare a body because it is not marked as abstract, partial or external. Why so 
        set
        {
            if (value == OpenMode.Add)
            {
                btnAddGuest.Text = "Save";
                btnUpdatePreference.Visible = false;
                dgvGuestInfo.ClearSelection();
            }
            else if (value == OpenMode.Update)
            {
                btnAddGuest.Text = "Update";
                btnUpdatePreference.Visible = true;
            }
        }
    }

Answer 1

You must implement both a getter and setter if you implement one of them. You can auto implement only both:

public OpenMode OpenFor
{
   get; 
   set;
}

You may consider to use a backing field:

private OpenMode openFor;

public OpenMode OpenFor
{
   get
   {
      return openFor;
   }
   set 
   {
      openFor = value;
      //...
   }
}