Someone

# cat hello2.c 
#include <gtk/gtk.h>
static void hello(GtkWidget *widget, gpointer data){
    g_print("Sergio Pinguim Filho eh o bom!\n");//imprimir mensagem
}
static gboolean delete_event(GtkWidget *widget,
                             GdkEvent *event,
                             gpointer data){
    g_print("Delete event ocurred\n");//imprimir mensagem
    return TRUE;
}
static void destroy(GtkWidget *widget, gpointer data)
{
    gtk_main_quit();//fechar a janela
}
int main(int argc, char *argv[]){
    GtkWidget *window;//declarando ponteiro para a janela
    GtkWidget *button;//declarando ponteiro para o botao
    GtkWidget *botao;
    GtkWidget *janela;
    gtk_init(&argc, &argv);
    window=gtk_window_new(GTK_WINDOW_TOPLEVEL);//cria a nova janela
    g_signal_connect(G_OBJECT(window), "delete_event", G_CALLBACK(delete_event), NULL);
    gtk_container_set_border_width(GTK_CONTAINER(window), 20); //tamanho da borda
    button=gtk_button_new_with_label("Oi mundo!");//cria o botão e define seus dizeres.
    g_signal_connect(G_OBJECT(button), "clicked", G_CALLBACK(hello), NULL);
    g_signal_connect_swapped(G_OBJECT(button), "clicked", G_CALLBACK(gtk_widget_destroy), G_OBJECT(window));
    gtk_container_add(GTK_CONTAINER(window), button);//coloca o botão dentro da janela
    botao=gtk_button_new_with_label("Clique!");
    g_signal_connect(G_OBJECT(botao), "clicked", G_CALLBACK(hello), NULL);
    g_signal_connect_swapped(G_OBJECT(botao), "clicked", G_CALLBACK(gtk_widget_destroy), G_OBJECT(window));
    gtk_container_add(GTK_CONTAINER(window), botao);
    gtk_widget_show(botao);
    gtk_widget_show(button);//abre o botão
    gtk_widget_show(window);//abre a janela
    gtk_main();//todos os códigos gtk tem que ter, equivale ao main()
    return 0;
}