openGL program : A Bouncing Ball

#include <GL/glut.h>
#include<math.h>
#define PI 3.1415926535898

GLfloat BXMAX,BXMIN,BYMAX,BYMIN;
GLint circle_points=100;
float rd=0.2;
GLfloat x=0.0,y=0.0;
GLdouble l,r,b,t;
GLfloat m = 0.02f;   
GLfloat n= 0.007f;


void initGL() {

   glClearColor(0.0, 0.0, 0.0, 1.0);
 glLoadIdentity();
 glMatrixMode(GL_PROJECTION);  
}


void idle() {
   glutPostRedisplay();  
}

void display() {
   glClear(GL_COLOR_BUFFER_BIT);  
               
      glPushMatrix();       
   glTranslatef(x, y, 0.00);   
   glBegin(GL_POLYGON);
    int i;
    float angle;
    glColor3f(1.0,0.0,0.0);
    for(i=0;i<circle_points;i++)
    {
    angle=2*PI*i/circle_points;
    glVertex2f((cos(angle))*rd,(sin(angle))*rd);
    }
   glEnd();
 glPopMatrix();
   glutSwapBuffers();  

   x=x+m;
  y=y+n;

if(x > BXMAX){
       m=-m;  
}else if(x < BXMIN){
       m=-m;
}if(y > BYMAX){
       n=-n;
}else if(y < BYMIN){
      n=-n;
}
}


void reshape(int width, int height) { 
   if (height == 0) height = 1;            
   GLfloat aspect = (GLfloat)width / (GLfloat)height;

 
   glViewport(0, 0, width, height);


   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   if (width >= height) {

      l=-1.0*aspect;
    r=1.0*aspect;
    b=-1.0;
    t=    1.0;

   } else {

    l=-1.0;
    r=1.0;
    b=-1.0/aspect;
    t=    1.0/aspect;
   }
gluOrtho2D(l,r,b,t);
BXMAX=r-(rd);
BXMIN=l+(rd);
BYMAX=t-(rd);
BYMIN=b+(rd); 

}



int main(int argc, char** argv) {
   glutInit(&argc, argv);         
   glutInitDisplayMode(GLUT_DOUBLE); 
   glutInitWindowSize(640, 480);  
   glutInitWindowPosition(50, 50);
   glutCreateWindow("ball");
 glutReshapeFunc(reshape); 

   glutDisplayFunc(display);       
   glutIdleFunc(idle);            
   initGL();                    
   glutMainLoop();                
   return 0;
}