movement - Unity3D move a sprite when pressing a key -

i'm trying move sprite when hit w key. have been using tutorial found on youtube , don't seem able make work. here code. perhaps i'm having problem transform; can see x position increments sprite doesn't anything.

#pragma strict  var startpoint : vector3; var endpoint : vector3; var speed : float; private var increment : float; var ismoving : boolean;  function start () {     startpoint = transform.position;     endpoint = transform.position; }  function update () {     if (increment <= 1 && ismoving == true) {         increment += speed/100;         debug.log("moving");      }     else {         ismoving = false;         debug.log("stopped");      }      if (ismoving == true)         transform.position = vector3.lerp(startpoint, endpoint, increment);      if (input.getkey("w") && ismoving == false) {         increment = 0;         ismoving = true;         startpoint = transform.position;         endpoint = new vector3(transform.position.x, transform.position.y, transform.position.z + 1);      }     if (input.getkey("s") && ismoving == false) {         increment = 0;         ismoving = true;         startpoint = transform.position;         endpoint = new vector3(transform.position.x, transform.position.y, transform.position.z - 1);     } } 

try this:

function update () {      if (input.getkeydown(keycode.w)) {         increment += speed / 100;         transform.position = vector3.lerp(transform.position, transform.position + vector3.forward, increment);     }      if (input.getkeydown(keycode.z)) {         increment += speed / 100;         transform.position = vector3.lerp(transform.position, transform.position + vector3.back, increment);     } } 

also, check speed not 0 in inspector. if wanna continuous movement change input.getkeydown input.getkey.