sscce.c

#include <gtk/gtk.h>
#include <stdio.h>

static GtkWidget *mainWindow = NULL;

void
prompt_window (void)
{
    GtkWidget *dialog = gtk_message_dialog_new (GTK_WINDOW (mainWindow),
        GTK_DIALOG_MODAL | GTK_DIALOG_DESTROY_WITH_PARENT,
        GTK_MESSAGE_INFO,
        GTK_BUTTONS_YES_NO,
        "What's the answer?");
    gtk_dialog_run (GTK_DIALOG (dialog));
    gtk_widget_destroy (dialog);
}

void
main_button_press (void)
{
    prompt_window ();
    prompt_window ();
}

int
main (int    argc,
      char **argv)
{
    gtk_init (&argc, &argv);
    mainWindow = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    GtkWidget *button = gtk_button_new_with_label ("Show two dialogs");
    g_signal_connect (G_OBJECT (mainWindow), "destroy",
        G_CALLBACK (gtk_main_quit), NULL);
    g_signal_connect (G_OBJECT (button), "clicked",
        G_CALLBACK (main_button_press), NULL);
    gtk_container_add (GTK_CONTAINER (mainWindow), button);
    gtk_widget_show_all (mainWindow);
    gtk_main ();
}