Toggle buttons and Entry widgets in GTK+

on_radio_capital_toggled(GtkToggleButton *togglebutton, gpointer user_data)
{
value=xyz;
}

void on_ok_button_clicked(GtkButton *button, gpointer user_data)
{
GtkWidget *entry;
GtkWidget *entry = (GtkWidget *) lookup_widget(GTK_WIDGET(button), “entrywidgetname”);
}