I am currently drawing a rectangle to the screen and would like to move it by using the arrow keys. However, when I press an arrow key the vertex data changes but the display does refresh to reflect these changes, even though I am calling glutPostRedisplay(). Is there something else that I must do?

My code:

#include <GL/glew.h>
#include <GL/freeglut.h>
#include <GL/freeglut_ext.h>
#include <iostream>
#include "Shaders.h"
using namespace std;

const int NUM_VERTICES = 6;
const GLfloat POS_Y = -0.1;
const GLfloat NEG_Y = -0.01;

struct Vertex {
    GLfloat x;
    GLfloat y;
    Vertex() : x(0), y(0) {}
    Vertex(GLfloat givenX, GLfloat givenY) : x(givenX), y(givenY) {}
};

Vertex left_paddle[NUM_VERTICES];

void init() {
    glClearColor(1.0f, 1.0f, 1.0f, 0.0f);

    left_paddle[0] = Vertex(-0.95f, 0.95f);
    left_paddle[1] = Vertex(-0.95f,  0.0f);
    left_paddle[2] = Vertex(-0.85f,  0.95f);
    left_paddle[3] = Vertex(-0.85f,  0.95f);
    left_paddle[4] = Vertex(-0.95f,  0.0f);
    left_paddle[5] = Vertex(-0.85f,  0.0f);

    GLuint vao;
    glGenVertexArrays( 1, &vao );
    glBindVertexArray( vao );

    GLuint buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(left_paddle), 
        NULL, GL_STATIC_DRAW);

    GLuint program = init_shaders( "vshader.glsl", "fshader.glsl" );
    glUseProgram( program );

    GLuint loc = glGetAttribLocation( program, "vPosition" );
    glEnableVertexAttribArray( loc );
    glVertexAttribPointer( loc, 2, GL_FLOAT, GL_FALSE, 0,
                           0);

    glBindVertexArray(vao);
}

void movePaddle(Vertex* array, GLfloat change) {
    for(int i = 0; i < NUM_VERTICES; i++) {
        array[i].y = array[i].y + change;
    }
    glutPostRedisplay();
}

void special( int key, int x, int y ) {
    switch ( key ) {
    case GLUT_KEY_DOWN:
        movePaddle(left_paddle, NEG_Y);
        break;
    }
}

void display() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glDrawArrays(GL_TRIANGLES, 0, 6);
    glutSwapBuffers();
}

int main(int argc, char **argv) {

    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
    glutInitWindowSize(500,500);
    glutCreateWindow("Rectangle");

    glewInit();
    init();

    glutDisplayFunc(display);  
    glutSpecialFunc(special); 

    glutMainLoop();
    return 0;

}