Computer Graphics Program in C to Simulate Motion of Simple Pendulum

In this post, we see a simple C program to simulate motion of a simple pendulum using graphics.h. Actually, this was a problem given in my CG lab (Computer Graphics lab). The program uses graphics.h header file. If you are using linux gcc, you have to include libgraph library. The header file graphics.h is already included in turboc or turboc++ compilers.

If you want corresponding java program, get it here: Java Program to Simulate Motion of Simple Pendulum.

The output of the program is as follows:

Program:

#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);
    

    }

}