Gtk example

# include <gtk/gtk.h>

void welcome (GtkButton *button, gpointer data)
{
    GtkWidget *dialog;
    GtkWidget *label;
    GtkWidget *content_area;

    dialog = gtk_dialog_new_with_buttons("Ошибка LOL!!!111",
                                         NULL,
                                         GTK_DIALOG_MODAL | GTK_DIALOG_DESTROY_WITH_PARENT,
                                         GTK_STOCK_OK,
                                         GTK_RESPONSE_ACCEPT,
                                         NULL);

    content_area = gtk_dialog_get_content_area(GTK_DIALOG(dialog));

    label = gtk_label_new("\n\nИ тебе привет, %username!%");
    gtk_container_add(GTK_CONTAINER(content_area), label);
    gtk_widget_show(label);

    gtk_dialog_run(GTK_DIALOG(dialog));
    gtk_widget_destroy(dialog);
}

int main( int argc, char *argv[])
{
    GtkWidget *button;
    GtkWidget *window;

    gtk_init(&argc, &argv);

    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title(GTK_WINDOW(window), "Введение в GTK");
    gtk_container_set_border_width (GTK_CONTAINER(window), 50);

    button = gtk_button_new_with_label("Привет, ХабраХабр!");
    gtk_container_add(GTK_CONTAINER(window), button);

    gtk_widget_show_all(window);

    g_signal_connect(G_OBJECT(window), "destroy", G_CALLBACK(gtk_main_quit), NULL);
    g_signal_connect(GTK_BUTTON(button), "clicked", G_CALLBACK(welcome), NULL);

    gtk_main();
    return 0;
}