get integer/real number from gtk_entry_set_text

[Rudra Banerjee <bnrj rudra yahoo com>]

Friends,
How can I convert gtk_entry_set_text to an integer/real number?
Below is a minimal example. Please suggest.
#include <stdio.h>
#include <gtk/gtk.h>

void enter_callback( GtkWidget *widget,
                     GtkWidget *entry )
{
  gchar *entry_text;
  entry_text = gtk_entry_get_text(GTK_ENTRY(entry));
  printf("Entry contents: %s\n", entry_text);
}

int main( int   argc,
          char *argv[] )
{

    GtkWidget *window;
    GtkWidget *vbox, *hbox;
    GtkWidget *entry;
    GtkWidget *button;
    GtkWidget *check;
    GtkWidget *table;
 
    gtk_init (&argc, &argv);

    /* create a new window */
    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title(GTK_WINDOW (window), "GTK Entry");
    gtk_signal_connect(GTK_OBJECT (window), "delete_event",
                       (GtkSignalFunc) gtk_exit, NULL);

/*  CREATE TABLE
 */

    table = gtk_table_new (5, 3, TRUE);
    gtk_container_add (GTK_CONTAINER (window), table);

/*
 *CREATE ENTRY FOR ATOM 1
 */
    entry = gtk_entry_new_with_max_length (2);
    gtk_table_attach_defaults (GTK_TABLE (table), entry, 0, 1, 0, 1);
    gtk_signal_connect(GTK_OBJECT(entry), "activate",
                       GTK_SIGNAL_FUNC(enter_callback),
                       entry);
    gtk_entry_set_text (GTK_ENTRY (entry), "A");
    gtk_widget_show (entry);

    gtk_widget_show (button);
    gtk_widget_show (table);
    gtk_widget_show(window);

    gtk_main();
    return(0);
}