Computer Graphics Program in C to Simulate Motion of Simple Pendulum

Computer Graphics Program in C to Simulate Motion of Simple Pendulum

#include<graphics.h>
#include<stdio.h>
#include<math.h>
#define PI 3.14

int gd=DETECT,gm;
int pivotx,pivoty;
double thetamax,theta;;
double len=260;
int x,y,ymax,xmax;
int bobradius=30;
int xsign=-1,ysign=1;
double omega;

void paint()
{
cleardevice();
setcolor(RED);
fillellipse(pivotx,pivoty,8,8);
line(pivotx,pivoty, x,y);
fillellipse(x,y,bobradius,bobradius);
}

void main()
{
 double decr;
 initgraph(&gd,&gm,"C:\\TURBOC3\\BGI\\");
 thetamax=60*PI/180;
 pivotx=getmaxx()/2;
 pivoty=30;
 ymax=(int) (pivoty+len*cos(thetamax));
 xmax=(int) (pivotx+len*sin(thetamax));
 x=xmax;
        y=ymax;
        theta=thetamax;

while(1)
      {
      if(x>=pivotx+abs(len*sin(thetamax)))
        {
        xsign=-1;
 ysign*=-1;
        x=xmax-1;
        delay(40);
        }
      else if(x<=pivotx-abs(len*sin(thetamax)))
      {
          ysign*=-1;
          xsign=1;
          x=(int) (pivotx-abs(len*sin(thetamax))+2);
          delay(40);
      }
      else if(y>=pivoty+len)
 {
              ysign*=-1;
        }

      omega=y/60*PI/180;
      decr=xsign*omega;
      theta=theta+decr;
      x=(int) (pivotx+len*sin(theta));
      y=(int) (pivoty+len*cos(theta));
      paint();
      delay(40);
    

    }

}