unity3d - Messing up Vectors in C# (Unity Engine) -

i'm new programming in c# in unity , there problems when moving in z-axis. problem continue move when let go of button. however, when move in x-axis fine, letting go of button stop player. code below:

using unityengine; using system.collections;  public class player : monobehaviour { public vector3 motion = new vector3(); private charactercontroller controller;  private bool onground;  private float xrot, yrot; public static float x_rotation = 0; public static float y_rotation = 0; private const float lookspeed = 2.0f;  public void start() {     controller = getcomponent<charactercontroller>(); }  public void fixedupdate() {     if(screen.lockcursor) {         vector3 impulse = new vector3();         if(input.getkey(keycode.w)) impulse.z+=1;         if(input.getkey(keycode.a)) impulse.x-=1;         if(input.getkey(keycode.s)) impulse.z-=1;         if(input.getkey(keycode.d)) impulse.x+=1;          if(impulse.sqrmagnitude > 0) {             motion += quaternion.euler(new vector3(0, xrot, 0)) * impulse.normalized * 0.05f;         }          if(onground) {             if(input.getkey(keycode.space)) {                 motion.y += 0.2f;             }         }          motion.y -= 0.015f;         vector3 oldmotion = motion;         vector3 oldpos = controller.transform.localposition;         controller.move(motion);         vector3 newpos = controller.transform.localposition;         motion = newpos - oldpos;         onground = oldmotion.y < -0.0001f && motion.y >= -0.0001f;         motion.x *= 0.8f;          motion.y *= 0.8f;     } }  public void update() {     if(screen.lockcursor && input.getkeydown(keycode.escape)) {         screen.lockcursor = false;       }      if(!screen.lockcursor && input.getmousebuttondown(0)) {         screen.lockcursor = true;        }      if(screen.lockcursor) {         xrot += input.getaxis("mouse x") * lookspeed;         yrot -= input.getaxis("mouse y") * lookspeed;          if(yrot < -90) yrot = -90;         if(yrot > 90) yrot = 90;         if(xrot < -180) xrot += 360;         if(xrot >= 180) xrot -= 360;          controller.transform.localrotation = quaternion.euler(new vector3(yrot, xrot, 0));     }      player.x_rotation = xrot; } 

}

the last few statments in fixedupdate() have coded-

motion.x *= 0.8f; motion.y *= 0.8f; 

should contain

motion.z *= 0.8f; 

and may u dont need-

motion.y *= 0.8f;