# cat hello.c 
#include <gtk/gtk.h>
static void hello(GtkWidget *widget, gpointer data){
    g_print("Hello World\n");
}
static gboolean delete_event(GtkWidget *widget,
                             Gdkevent *event,
                             gpointer data){
    g_print("Delete event ocurred\n");
    return TRUE;
}
static void destroy(GtkWidget *widget, gpointer data)
{
    gtk_main_quit();
}
int main(int argc, char *argv[]){
    GtkWidget *window;
    GtkWidget *button;
    gtk_init(&argc, &argv);
    window=gtk_window_new(GTK_WINDOW_TOPLEVEL);
    g_signal_connect(G_OBJECT(window), "delete_event", G_CALLBACK(delete_event), NULL);
    gtk_container_set_border_width(GTK_CONTAINER(window), 10); //border width
    button=gtk_button_new_with_label("Oi mundo!");
    g_signal_connect(G_OBJECT(button), "clicked", G_CALLBACK(hello), NULL);
    g_signal_conect_swapped(G_OBJECT(button), "clicked", G_CALLBACK(gtk_widget_destroy), G_OBJECT(window));
    gtk_container_add(GTK_CONTAINER(window), button);
    gtk_widget_show(button);
    gtk_widget_show(window);
    gtk_main();
    return 0;
}