Small problem with drawing line...

[Mariusz Bozewicz <plachninka wp pl>]

Hi
Another problem. I want to draw line with using gdk_draw_line. Tutorials
don't tell me how and what i should do.... I'm looking for some onlina
papers, books, tutorials, short examples about graphic in GTK (GDK)

GtkWidget *drawarea;
drawarea=gtk_drawing_area_new();
gtk_drawing_area_size(GTK_DRAWING_AREA(drawarea),300,300);
gdk_draw_line(drawarea->window,drawarea->style->black_gc,
                10,10,100,100);
gtk_widget_show(drawarea);

when I run program with this piece of code it returns error:
GDK-CRITICAL ** file gdkdraw.c: line 65 (gdk_draw_line): assertion
'drawable !=NULL' failed

Question: what is wrong with this code? How can I use graphic function?
  tutorials, something online please....
                                 Mariusz Bozewicz