OpenGL - 2D Movement with respondtokeypress

[MrBawzz]

Hello,

I'm trying to implement keyboard controls to move a sphere(Player) with respondtokeypress.
Currently, when I press any key my character will move to the right by 0.1. This might be a noobie question but how can I move my character with w(up),a(left),s(down),d(right) in their respective directions using respondtokeypress?

class Player
{
private:
  double x, y;
public:
  Player(double a, double b){x=a;y=b;} 
      void respondtokeypress(char a)
  {
	  a +=0.1;
	  a -=0.1;
	  b +=0.1;
	  b -=0.1;
	  glutPostRedisplay();
  }
  void draw()
  {
   //draw player 
   glLoadIdentity();
   glColor3f (1.0, 0.0, 0.0);
   glTranslatef(x,y,0);
   glutSolidSphere(0.03,20,20);
  }
};

void keyboard(unsigned char key, int x, int y)
{      
Theseus.respondtokeypress(key);
        glutPostRedisplay();
}