Sine

/*

 * THIS IS A C PROGRAM THAT ANIMATES THE MOTION OF A CIRCULAR BALL ACROSS A SINE WAVE.

* THE BALL REMAINS IN CONTACT WITH THE SINE CURVE AT EVERY INSTANT AND TRAVELS FROM

* X = -π TO X = π ONCE

 */

#include<stdlib.h>

#include<conio.h>

#include<graphics.h>

#include<math.h>

#include<dos.h>

void drawsinewave();

void drawaxes();

void linejoin(double, double, double, double);

void drawball(double);

void animateball(void);

int main(void)

{

  /* request auto detection */

   int gdriver = DETECT, gmode, errorcode;

   /* clear screen */

   clrscr();

   /* 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();

   /* terminate with an error code */

      exit(1);

   }

   animateball();  

   getch();

   return 0;

}

/* following function draws the X and Y axes */

void drawaxes()

{

            setcolor(WHITE);

            line(getmaxx()/2, 0, getmaxx()/2, getmaxy());    /* drawing Y axis */

            line(0, getmaxy()/2, getmaxx(), getmaxy()/2);    /* drawing X axis */

}

/* following function performs the animation */

void animateball()

{

            double x;

           

            for(x=-M_PI;x<=M_PI;x+=0.01)

            {

                        drawaxes();

                        drawsinewave();

                        setcolor(WHITE);

                        drawball(x);                             /* draw the ball */

                        delay(50);                                 /* give a delay before next movement */

                        setcolor(BLACK);                                  /* remove traces of the drawn ball */

                        drawball(x);

            }

}

/* following function draws the sine wave across the screen */

void drawsinewave()

{

  double oldx = -M_PI, oldy=sin(oldx), x, y;

 

  setcolor(WHITE);

  do

  {

              x=oldx+0.01;

              y=sin(x);

              linejoin(x,y,oldx,oldy);

              oldx=x;

              oldy=y;

  }while(x<=M_PI);

}

/* following function joins two points given in rectangular Cartesian co-ordinate systems */

void linejoin(double x1, double y1, double x2, double y2)

{

            double xscale = 100, yscale = getmaxy()/2.5 ;

            int newx1 = x1*xscale + getmaxx()/2 ;

            int newy1 = -y1*yscale + getmaxy()/2 ;

            int newx2 = x2*xscale + getmaxx()/2 ;

            int newy2 = -y2*yscale + getmaxy()/2 ;

            line(newx1, newy1, newx2, newy2);

}

/* following function draws the ball at a given abscissa */

void drawball(double x)        

{

 double y = sin(x), xscale = 100, yscale = getmaxy()/2.5, xshift = getmaxx()/2, yshift = getmaxy()/2;

 double Xknown = x*xscale + xshift, Yknown = -y*yscale + yshift;

 double R = 10;

 double deno = sqrt(yscale*yscale*cos(x)*cos(x)+xscale*xscale);

 double Xcentre = Xknown - R*yscale*cos(x)/deno;

 double Ycentre = Yknown - R*xscale*cos(x)/(deno*cos(x));

 circle(Xcentre,Ycentre,R);

}