How to open and close a modal window in Glade with C

I'm trying to do this using show-hide.

To open a window (show the window)
In Glade
For main window GtkImageMenuItem, set its ID to: helpabout
For main window Signals, activate, set: handler on_helpabout_activate, data about
Create a GtkWindow ID: about. Window flags: remove deletable, add modal
In C

void on_helpabout_activate(GtkMenuItem *helpabout, GtkWidget *a)
{
    printf("Showing about\n");
    gtk_widget_show (a);
}

To close a window (hide the window)
In Glade
For window about, add a button ID: butt
For butt Signals, clicked, set: handler on_butt_clicked, data about
In C

void on_butt_clicked (GtkButton *butt, GtkWidget *a)
{
    printf("Hiding about\n");
    gtk_widget_hide (a);
}