Rotating Coin Animation

#include<stdio.h>
#include<graphics.h>
#include<conio.h>
#include<dos.h>

void put_pixel(const int h,const int k,const int x,const int y,int color)
{
 putpixel((getmaxx()/2)+(h+x),(getmaxy()/2)-(k+y),color);
 putpixel((getmaxx()/2)+(h+x),(getmaxy()/2)-(k-y),color);
 putpixel((getmaxx()/2)+(h-x),(getmaxy()/2)-(k-y),color);
 putpixel((getmaxx()/2)+(h-x),(getmaxy()/2)-(k+y),color);
}

void midpoint_ellipse(const int h,const int k,const int a,const int b,int col)
{
 float aa=(a*a);
 float bb=(b*b);
 float aa2=(aa*2);
 float bb2=(bb*2);
 float x=0;
 float y=b;
 float fx=0;
 float fy=(aa2*b);
 float p=(int)(bb-(aa*b)+(0.25*aa)+0.5);
 put_pixel(h,k,x,y,col);
 while(fx<fy)
 {
  x++;
  fx+=bb2;
  if(p<0)
   p+=(fx+bb);
  else
  {
   y--;
   fy-=aa2;
   p+=(fx+bb-fy);
  }
  put_pixel(h,k,x,y,col);
 }
 p=(int)((bb*(x+0.5)*(x+0.5))+(aa*(y-1)*(y-1))-(aa*bb)+0.5);
 while(y>0)
 {
  y--;
  fy-=aa2;
  if(p>=0)
    p+=(aa-fy);
  else
  {
   x++;
   fx+=bb2;
   p+=(fx+aa-fy);
  }
  put_pixel(h,k,x,y,col);
 }
}

void init_graph()
{
 int gdriver = DETECT, gmode, errorcode;
 initgraph(&gdriver, &gmode, "");
 errorcode = graphresult();
 if (errorcode != grOk)  /* an error occurred */
 {
   printf("Graphics error: %s\n", grapherrormsg(errorcode));
   printf("Press any key to halt:");
   getch();
 }
}

void main()
{
 init_graph();
 int h =0;
 int k =0;
 int rx = 100;
 int ry = 100;
 int rdx = -2;
 do
 {
  rx += rdx;
  if(rx == 0 || rx == 100)
    rdx *= -1;
  midpoint_ellipse(h,k,rx,ry,RED);
  delay(10);
  cleardevice();
 }while(!kbhit());
 getch();
}