Open GL Program to display a Clock

#include<GL/glut.h>

float theta = 0.0, thetar;
int flag=0;
void mydisplay(void)
{
   
     float cx=-0.0,cy=0.0, r=1;
     int num_segments=80;
     int i;
     glClear(GL_COLOR_BUFFER_BIT);
     glBegin(GL_LINES);
    thetar=theta*(3.14/180);
        glColor3f(0.0, 1.0, 0.0);
        glVertex2f(0.0, 0.0);
        glColor3f(0.0, 1.0, 0.0);
        glVertex2f(-sin(thetar), cos(thetar));
       
     glEnd();
 
     glBegin(GL_LINE_LOOP);
     for(i = 0; i<num_segments; i++)
     {
        float theta1;
        theta1 = (2.0 * 3.1415926 * (i)) / (num_segments);
        float x = r * cosf(theta1);
        float y = r * sinf(theta1);
        glVertex2f(x + cx, y + cy);
     }
     glEnd();
     glutSwapBuffers();
}

void spinDisplay(void)
{
  theta -= 0.1;
  if (theta < 360.0)
      theta += 360.0;
  glutPostRedisplay();
}


int main(int argc, char **argv)
{
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
  glutInitWindowPosition(150, 150);
  glutInitWindowSize(500,500);
  glutCreateWindow("Clock");
  glutDisplayFunc(mydisplay);
  glutIdleFunc(spinDisplay);
  glutMainLoop();
  return 0;
}



                                                        OUTPUT