GTK simple button error

In file included from /usr/include/gtk-3.0/gtk/gtkaccellabel.h:36:0,
                 from /usr/include/gtk-3.0/gtk/gtk.h:33,
                 from GTKsimple.c:1:
/usr/include/gtk-3.0/gtk/gtklabel.h:41:27: error: expected declaration specifiers or ‘...’ before ‘(’ token
 #define GTK_LABEL(obj)    (G_TYPE_CHECK_INSTANCE_CAST ((obj), GTK_TYPE_LABEL, GtkLabel))
                           ^
GTKsimple.c:5:18: note: in expansion of macro ‘GTK_LABEL’
 void updateLabel(GTK_LABEL(sum), int num)
                  ^
In file included from /usr/include/gtk-3.0/gtk/gtkbin.h:33:0,
                 from /usr/include/gtk-3.0/gtk/gtkwindow.h:35,
                 from /usr/include/gtk-3.0/gtk/gtkdialog.h:33,
                 from /usr/include/gtk-3.0/gtk/gtkaboutdialog.h:30,
                 from /usr/include/gtk-3.0/gtk/gtk.h:31,
                 from GTKsimple.c:1:
GTKsimple.c: In function ‘main’:
/usr/include/gtk-3.0/gtk/gtkcontainer.h:39:41: warning: passing argument 1 of ‘gtk_widget_set_size_request’ from incompatible pointer type
 #define GTK_CONTAINER(obj)              (G_TYPE_CHECK_INSTANCE_CAST ((obj), GTK_TYPE_CONTAINER, GtkContainer))
                                         ^
GTKsimple.c:50:37: note: in expansion of macro ‘GTK_CONTAINER’
     gtk_widget_set_size_request    (GTK_CONTAINER(window), 150, 100);
                                     ^
In file included from /usr/include/gtk-3.0/gtk/gtkapplication.h:27:0,
                 from /usr/include/gtk-3.0/gtk/gtkwindow.h:33,
                 from /usr/include/gtk-3.0/gtk/gtkdialog.h:33,
                 from /usr/include/gtk-3.0/gtk/gtkaboutdialog.h:30,
                 from /usr/include/gtk-3.0/gtk/gtk.h:31,
                 from GTKsimple.c:1:
/usr/include/gtk-3.0/gtk/gtkwidget.h:964:12: note: expected ‘struct GtkWidget *’ but argument is of type ‘struct GtkContainer *’
 void       gtk_widget_set_size_request    (GtkWidget           *widget,
            ^