circle drawing in openGL

// tree.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <stdlib.h> //Needed for "exit" function
#include "math.h"

//Include OpenGL header files, so that we can use OpenGL
#ifdef __APPLE__
#include <OpenGL/OpenGL.h>
#include <GLUT/glut.h>
#else
#include "glut.h"
#endif

using namespace std;


void drawCircle(float radius, float x1, float y1)
{
 float angle = 0;
 float x2,y2,cx,cy,fx,fy;
 int cache = 0;
 glBegin(GL_LINES);
 for (angle = 0; angle < 360; angle+=1.0) {
  float rad_angle = angle * 3.14 / 180;
  x2 = radius * sin((double)rad_angle);
  y2 = radius * cos((double)rad_angle);
  if (cache) {
   glVertex2f(cx,cy);
   glVertex2f(x2,y2);
  } else {
   fx = x2;
   fy = y2;
  }
  cache = 1;
     cx = x2;
  cy = y2;
 }
 glVertex2f(x2,y2);
 glVertex2f(fx,fy);

 glEnd();
}

void display(void) {
 glClearColor (0.0,0.0,0.0,1.0);
 glClear (GL_COLOR_BUFFER_BIT);
 glLoadIdentity();
 glTranslatef(-10,0,-30);
 glColor3f(1,0,0);
 drawCircle(10,0,0);
 glutSwapBuffers();
}

void reshape (int w, int h) {
 glViewport (0, 0, (GLsizei)w, (GLsizei)h);
 glMatrixMode (GL_PROJECTION);
 glLoadIdentity ();
 gluPerspective (60, (GLfloat)w / (GLfloat)h, 0.1, 100.0);
 glMatrixMode (GL_MODELVIEW);
}

void keyboard(unsigned char key, int x, int y)
{
   switch (key) {
      case 27:
         exit(0);
         break;
   }
}

int main (int argc, char **argv) {
 glutInit (&argc, argv);
 glutInitDisplayMode (GLUT_DOUBLE);
 glutInitWindowSize (1200, 800);
 glutInitWindowPosition (0, 0);
 glutCreateWindow ("A Pendulum");

 glutDisplayFunc (display);
 glutIdleFunc (display);
 glutReshapeFunc (reshape);
    glutKeyboardFunc (keyboard);
 glutMainLoop ();
 return 0;
}