continuous updating of screen

I have the following main and some functions. the roam() handles keystrokes. I change my camera's location based on the key strokes but the window is not updated after each key stroke. I have to resize the window to update the screen. can any one tell me what is wrong here?

int main(int argc, char **argv)
{
  glutInit(&argc, argv);
  glutInitWindowSize(600,600);
  glutInitDisplayMode(GLUT_DEPTH);
  glEnable(GL_DEPTH_TEST);
  glutCreateWindow("two polygons");
  glutDisplayFunc(display);
  glutReshapeFunc(reshape);
  glutSpecialFunc(roam);
  glutMainLoop();
  return 0;             /* ANSI C requires main to return int. */
}

void reshape(int w, int h){...}
void display(void){...}
void roam(int key, int x, int y){
  switch(key){
    ...
  }
  reshape(w, h);
}