Update Tutorial.md [skip ci]

docs/markdown/Tutorial.md

@@ -29,8 +29,11 @@ example. First we create a file `main.c` which holds the source. It
 looks like this.
 
 ```c
-#include<stdio.h>
+#include <stdio.h>
 
+//
+// main is where all program execution starts
+//
 int main(int argc, char **argv) {
   printf("Hello there.\n");
   return 0;
@@ -53,7 +56,7 @@ to initialize the build by going into the source directory and issuing
 the following commands.
 
 ```console
-$ meson builddir
+$ meson setup builddir
 ```
 
 We create a separate build directory to hold all of the compiler
@@ -110,17 +113,40 @@ create a graphical window instead. We'll use the
 use GTK+. The new version looks like this.
 
 ```c
-#include<gtk/gtk.h>
 
-int main(int argc, char **argv) {
-  GtkWidget *win;
-  gtk_init(&argc, &argv);
-  win = gtk_window_new(GTK_WINDOW_TOPLEVEL);
-  gtk_window_set_title(GTK_WINDOW(win), "Hello there");
-  g_signal_connect(win, "destroy", G_CALLBACK(gtk_main_quit), NULL);
-  gtk_widget_show(win);
-  gtk_main();
-}
+#include <gtk/gtk.h>
+
+//
+// Should provided the active view for a GTK application 
+//
+static void activate(GtkApplication* app, gpointer user_data)
+{
+  GtkWidget *window;
+  GtkWidget *label;
+
+  window = gtk_application_window_new (app);
+  label = gtk_label_new("Hello GNOME!");
+  gtk_container_add (GTK_CONTAINER (window), label);
+  gtk_window_set_title(GTK_WINDOW (window), "Welcome to GNOME");
+  gtk_window_set_default_size(GTK_WINDOW (window), 200, 100);
+  gtk_widget_show_all(window);
+} // end of function activate
+
+//
+// main is where all program execution starts
+//
+int main(int argc, char **argv)
+{
+  GtkApplication *app;
+  int status;
+
+  app = gtk_application_new(NULL, G_APPLICATION_FLAGS_NONE);
+  g_signal_connect(app, "activate", G_CALLBACK(activate), NULL);
+  status = g_application_run(G_APPLICATION(app), argc, argv);
+  g_object_unref(app);
+
+  return status;
+} // end of function main
 ```
 
 Then we edit the Meson file, instructing it to find and use the GTK+