gtk_drawing_area_size first parameter
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Hello guys I'm using c++ and gtk+ 2 I want to make a simple paint program like MS program but by these two tools only okay I just started and I want your hands to reach the end :) 
look to my code here 

    #include <gtk/gtk.h>
    int main( int argc,char *argv[] )
    {
    GtkWidget* window;
    GtkWidget* drawingArea;
    gtk_init (&argc, &argv);
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    g_signal_connect (G_OBJECT (window), "delete_event",G_CALLBACK (gtk_main_quit), G_OBJECT(window));
    g_signal_connect (G_OBJECT (window), "destroy",G_CALLBACK (gtk_main_quit), G_OBJECT(window));
    gtk_container_set_border_width (GTK_CONTAINER (window), 10);
    
    drawingArea = gtk_drawing_area_new();
    /*The problem is in the next line*/
    gtk_drawing_area_size(G_OBJECT(drawingArea),200,200);
    
    
    gtk_container_add (GTK_CONTAINER (window), drawingArea);
    gtk_widget_show (drawingArea);
    
    
    
    gtk_widget_show (window);
    gtk_main ();
    return 0;
    }
my problem is in the commented line 

    gtk_drawing_area_size(G_OBJECT(drawingArea),200,200);
the error when compiling 

     ibrahim@ibrahim-PC:~/Desktop$ gcc main.cpp -o base `pkg-config --cflags --libs gtk+-2.0`
    main.cpp: In function ‘int main(int, char**)’:
    main.cpp:14:52: error: cannot convert ‘GObject* {aka _GObject*}’ to ‘GtkDrawingArea* {aka _GtkDrawingArea*}’ for argument ‘1’ to ‘void gtk_drawing_area_size(GtkDrawingArea*, gint, gint)’

So Please help me 