编译后运行，说“BGI Error:Graphics not initialized<use 'initgraph'>”，这是为什么呢？
#include "graphics.h"
#include "stdio.h"
main()
{int x=100,y=100,graph=VGA,mode=VGAHI;
 cleardevice();
 initgraph(&graph,&mode,"");
 line(1,1,x,y);
 getch();
}