VAO with index

#include <iostream>
#include <math.h>
#if ( (defined(__MACH__)) && (defined(__APPLE__)) )   
#include <stdlib.h>
#include <OpenGL/gl.h>
#include <GLUT/glut.h>
#include <OpenGL/glext.h>
#else
#include <stdlib.h>
#include <GL/glew.h>
#include <GL/gl.h>
#include <GL/glut.h>
#include <GL/glext.h>
#endif

using namespace std;

const char *VERTEX_SHADER_SOURCE =                "\n" \
"layout(location = 0) in vec3 pos; \n" \
"layout(location = 1) in vec3 color; \n" \
"uniform vec3 translate; \n" \
"out vec4 v_pos;                               \n" \
"out vec4 v_color;                             \n" \
"void main ()                                      \n" \
"{                                                 \n" \
"   gl_Position = vec4(pos+translate, 1.0);                  \n" \
"   v_pos = gl_Position;                        \n" \
"   v_color = vec4(color.r, color.g, color.b, 1.0);  \n" \
"}                                                 \n" \
"\n";

const char * FRAGMENT_SHADER_SOURCE =    "\n" \
"varying vec4 v_pos;                    \n" \
"varying vec4 v_color;                    \n" \
"void main ()                             \n" \
"{                                        \n" \
"   gl_FragColor = v_color;               \n" \
"}                                        \n" \
"\n";

GLfloat vertices[12] = {
   -0.5f, -0.5f, 0.0f, 
   -0.5f, 0.5f, 0.0f,
   0.5f, 0.5f, 0.0f,
   0.5f, -0.5f, 0.0f 
};

GLfloat colors1[12] = {
   1.0f, 0.0f, 0.0f, 
   1.0f, 0.0f, 0.0f,
   0.0f, 0.0f, 1.0f,
   0.0f, 0.0f, 1.0f 
};

GLfloat colors2[12] = {
   0.0f, 1.0f, 0.0f, 
   0.0f, 1.0f, 0.0f,
   0.0f, 0.2f, 0.0f,
   0.0f, 0.2f, 0.0f 
};

GLuint indices[4] = { 0, 1, 2, 2 };

GLuint theShaderProgram;
GLuint theIndexVBO;
GLuint theVertexVBO;
GLuint theColor1VBO;
GLuint theColor2VBO;

GLuint theVAO1;
GLuint theVAO2;

void MakeVAO(GLuint vao, GLuint indexVBO, GLuint vertexVBO, GLuint colorVBO)
{
   glBindVertexArray(vao);

   glBindBuffer(GL_ARRAY_BUFFER, vertexVBO);
   glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, NULL);

   glBindBuffer(GL_ARRAY_BUFFER, colorVBO);
   glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, NULL);

   glEnableVertexAttribArray(0);
   glEnableVertexAttribArray(1);   
}

void DefineUnitQuad ()
{
   glGenBuffers(1, &theVertexVBO); 
   glBindBuffer(GL_COPY_WRITE_BUFFER, theVertexVBO);
   glBufferData(GL_COPY_WRITE_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

   glGenBuffers(1, &theColor1VBO); 
   glBindBuffer(GL_COPY_WRITE_BUFFER, theColor1VBO);
   glBufferData(GL_COPY_WRITE_BUFFER, sizeof(colors1), colors1, GL_STATIC_DRAW);

   glGenBuffers(1, &theColor2VBO); 
   glBindBuffer(GL_COPY_WRITE_BUFFER, theColor2VBO);
   glBufferData(GL_COPY_WRITE_BUFFER, sizeof(colors2), colors2, GL_STATIC_DRAW);

   glGenBuffers(1, &theIndexVBO);
   glBindBuffer(GL_COPY_WRITE_BUFFER, theIndexVBO);
   glBufferData(GL_COPY_WRITE_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
   
   glGenVertexArrays(1, &theVAO1);
   MakeVAO(theVAO1, theIndexVBO, theVertexVBO, theColor1VBO);

   glGenVertexArrays(1, &theVAO2);
   MakeVAO(theVAO2, theIndexVBO, theVertexVBO, theColor2VBO);
}

void InitCanvas()
{
  glViewport(0, 0, 500, 500);
  glClearColor(0.1, 0.1, 0.1, 1.0); 

  DefineUnitQuad();

  GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
  glShaderSource(vertexShader, 1, &VERTEX_SHADER_SOURCE, NULL);
  glCompileShader(vertexShader);

  // catch vertex shader compilation error
  GLint success;
  GLchar infoLog[512];
  glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
  if (!success)
  {
    glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
    std::cout << "Vertex shader did not compile\n" << infoLog << std::endl;
  }

  GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
  glShaderSource(fragmentShader, 1, &FRAGMENT_SHADER_SOURCE, NULL);
  glCompileShader(fragmentShader);

  // catch fragment shader compilation error
  glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
  if (!success)
  {
    glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
    std::cout << "Fragment shader did not compile\n" << infoLog << std::endl;
  }

  theShaderProgram = glCreateProgram();
  glAttachShader(theShaderProgram, vertexShader);
  glAttachShader(theShaderProgram, fragmentShader);
  glLinkProgram(theShaderProgram);

  // catch program linking error
  glGetProgramiv(theShaderProgram, GL_LINK_STATUS, &success);
  if (!success)
  {
    glGetProgramInfoLog(theShaderProgram, 512, NULL, infoLog);
    std::cout << "Shader program did not link\n" << infoLog << std::endl;
  }

  glDeleteShader(vertexShader);
  glDeleteShader(fragmentShader);
}

void Timer(int vp_time)
{
  glutPostRedisplay();
  glutTimerFunc(100, Timer, 0);
}

void Draw ()
{
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  glMatrixMode(GL_PROJECTION);
  glLoadIdentity(); 
  glOrtho(-1.0, 1.0, -1.0, 1.0, -10, 10);

  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity(); 
  glUseProgram(theShaderProgram);

  GLuint uniAttrLoc = glGetUniformLocation(theShaderProgram, "translate");

  glUniform3f(uniAttrLoc, -0.25f, -0.25f, 0.0f);
  glBindVertexArray(theVAO1);
  glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, theIndexVBO);
  glDrawElements(GL_TRIANGLE_FAN, 4, GL_UNSIGNED_INT, (void*) 0);

  glUniform3f(uniAttrLoc, 0,0,0); //0.25f, 0.25f, 0.0f);
  glBindVertexArray(theVAO2);
  glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, theIndexVBO);
  glDrawElements(GL_TRIANGLE_FAN, 4, GL_UNSIGNED_INT, (void*) 0);

  glFlush();
}

int main (int argc, char *argv[])
{
   glutInit(&argc, argv);
   glutInitDisplayMode(GLUT_RGBA);
   glutInitWindowSize(500, 500);
   glutInitWindowPosition(0, 0);
   glutCreateWindow("helloGL");

   glewInit();
   if (glewIsSupported("GL_VERSION_2_0"))
   {
      cout << "Ready for OpenGL 2.0\n";
   }
   else 
   {
      cout << "OpenGL 2.0 not supported\n";
      exit(1);
   }

   InitCanvas();
   glutTimerFunc(100, Timer, 0);
   glutDisplayFunc(Draw);
   glutMainLoop();

   return 0;
}