#include <graphics.h>
main()
{
 int gdriver,gmode,i;
 gdriver=DETECT;
 registerbgidriver(EGAVGA_driver);
 initgraph(&gdriver,&gmode,"");
 setbkcolor(0);
 cleardevice();
 for (i=0;i<15;i++);
    {
     setbkcolor(i);
     circle(320,240,20+i*10);
     delay(100);
    }
 for (i=0;i<15;i++)
    {
     cleardevice();
     setcolor(i);
     circle(320,240,20+i*10);
     delay(100);
    }
 closegraph();
 return 0;
}
当我运行完这个程序的时候怎么不能正常退出,总是黑屏,但没死机,就是看不到屏幕