#include <graphics.h> void circle(int x, int y, int radius);
The linestyle parameter does not affect arcs, circles, ellipses, or pie slices. Only the thickness parameter is used.
If your circles are not perfectly round, adjust the aspect ratio.
/* circle example */ 
#include <graphics.h>
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>
int main(void)
{
   /* request autodetection */
   int gdriver = DETECT, gmode, errorcode;
   int midx, midy, radius = 100;
   /* initialize graphics and local variables */
   initgraph(&gdriver, &gmode, "");
   /* read result of initialization */
   errorcode = graphresult();
   if (errorcode != grOk) {   /* an error occurred */
      printf("Graphics error: %s\n", grapherrormsg(errorcode));
      printf("Press any key to halt:");
      getch();
      exit(1);               /* terminate with an error code */
   }
   midx = getmaxx() / 2;
   midy = getmaxy() / 2;
   setcolor(getmaxcolor());
   /* draw the circle */
   circle(midx, midy, radius);
   /* clean up */
   getch();
   closegraph();
   return 0;
}