g_signal_connect(button, "clicked", G_CALLBACK(print_hello), NULL);
g_signal_connect_swapped(button, "clicked", G_CALLBACK(gtk_widget_destroy),
window);
g_signal_connect(button, "clicked", G_CALLBACK(print_hello), NULL);
g_signal_connect_swapped(button, "clicked", G_CALLBACK(gtk_widget_destroy),
window);