OpenGL Program for sine wave

// 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 <windows.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;

float rotate =0.0;

float start = 0.0;
void drawSinWave()
{
 float radius = 7.5;
 float x2=0,y2,cx,cy,fx,fy;
 float cos_y,cache_cos_y;
 int cache = 0;
 start += 1.0;
 if(start >360) {
  start = 0;
 }
 glBegin(GL_LINES);
 float angle = 0;
 for(angle=start; ; angle+=1.0) {
  if(angle>1020) {
   break;
   angle = 0.0;
  }
  float rad_angle = angle * 3.14 / 180;
  x2 = x2+0.1;
  y2 = radius * sin((double)rad_angle);
  cos_y = radius * sin((double)-rad_angle);
  if (cache) {
   glVertex2f(cx,cy);
   glVertex2f(x2,y2);
   
   glVertex2f(cx,cache_cos_y);
   glVertex2f(x2,cos_y);

  } else {
   fx = x2;
   fy = y2;
  }
  cache = 1;
  cx = x2;
  cy = y2;
  cache_cos_y = cos_y;
 }
 glEnd();
}

void display(void) {
 glClearColor (0.0,0.0,0.0,1.0);
 glClear (GL_COLOR_BUFFER_BIT);
 glLineWidth(10);
 glLoadIdentity();
 glTranslatef(-40,0,-30);
 glColor3f(1,0,0);
 
 drawSinWave();
 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 Sine wave");

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