пример GtkProgressBar

#include <gtk/gtk.h>

gboolean sf (gpointer data) {
  static gint count = 0;
  GtkProgressBar *pb = GTK_PROGRESS_BAR (data);

  if (count == 100)
    {
      gtk_main_quit();
      return FALSE;
    }

  gtk_progress_bar_set_fraction (pb, (gdouble) count / 100);
  count++;

  return TRUE;
}

int main (int argc, char *argv[])
{
  GtkWidget *w, *pb;

  gtk_init (&argc, &argv);

  w = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  g_signal_connect (G_OBJECT (w), "destroy", G_CALLBACK (gtk_main_quit), NULL);
  pb = gtk_progress_bar_new ();
  gtk_container_add (GTK_CONTAINER (w), pb);
  gtk_widget_show_all (w);

  g_timeout_add_seconds (1, sf, pb);

  gtk_main ();

  return 0;
}