#include <dos.h>
#include <math.h>
#include <conio.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>


#include <graphics.h>


int    GraphDriver;		/* The Graphics device driver		*/
int    GraphMode, ErrorCode;
void Initialize(void)
{
  int xasp, yasp;			/* Used to read the aspect ratio*/

  GraphDriver = DETECT; 		/* Request auto-detection	*/
  initgraph( &GraphDriver, &GraphMode, "" );
  ErrorCode = graphresult();		/* Read result of initialization*/
  if( ErrorCode != grOk ){		/* Error occured during init	*/
    printf(" Graphics System Error: %s\n", grapherrormsg( ErrorCode ) );
    exit( 1 );
  }
}


void assi()
{
	line(0,239,639,239);
	line(319,0,319,479);
}


void punto(float x, float y)
{
  putpixel(int(x)+319,int(239-y),2);
}

void cerchio(float x, float y, int r)
{
	circle(int(x)+319,int(239-y),r);
}


void testo(float x, float y, char *s)
{
  outtextxy(int(x)+319,int(239-y),s);
}


int segno(float y)
{
	if(y>0)
	  return 1;
	if(y==0)
	  return 0;
	if(y<0)
	  return -1;
}

void main()
{
    int i;
    float x,y;
    int segnoy;

    Initialize();
    assi();
    y=0.1F*(-100)*(-100)-16;
    for (x=-100; x<=100 ; x=x+0.1F)
    {
	segnoy=segno(y);
	y=0.1F*x*x-16;
	if (segnoy!=segno(y))
		cerchio(x,y,5);
	punto(x,y);
	delay(10);
    }
   getch();
}