How do I change animation states... or is there a better way?

Hi there, I have been trying to find a way to animate a spritesheet using Unity's built in animator. So far the best way I have come across is in my code below (Switching animation states using an integer). However the animation is not switching states properly. Example: When I press walk, it walks... but then it will not STOP walking. Can anyone help show me what I am doing wrong here... or if they know of a better way to animate sprites in script the help would be appreciated:D Also, thanks in advanced for any help!

(Please note: I would like to keep variables such as walk speed separate from the animator parameters.)

Complete Character Controls Script:

 //Player Controls Script:
 //-----------------------
 
 //----------------------
 //Public Variables
 //----------------------
 
 var walkSpeed                    : float = 4.0;        //Walking Speed
 var runSpeed                    : float = 4.0;        //Runninging speed
 var fallSpeed                    : float = 2.0;        //Character fall speed
 var jumpHeight                    : float = 10.0;        //How high the character can jump
 var gravity                        : float = 20.0;        //Gravity
 var startPos                    : float = 0.0;
 
 //--------------------
 //Is/Enabled Variables
 //--------------------
 
 private var crouchEnabled        : boolean = true;
 private var jumpEnabled            : boolean = true;
 private var idleEnabled            : boolean = true;
 
 private var isCrouching            : boolean = false;
 private var isJumping            : boolean = false;
 private var isWalking            : boolean = false;
 
 //---------------------
 //Storage Variables
 //---------------------
 
 var moveDirection                : int = 1;        //Dictates which direction the character faces when the game starts
 
 private var velocity            : Vector3 = Vector3.zero;    //Stores numbers
 private var afterHitForceDown    : float = 1.0;                //After it collides, force the player down variable
 
 //---------------------------------
 //Player Animation State Variables
 //---------------------------------
 
 private var state_Idle        : int = 0;
 private var state_Walk        : int = 1;
 private var state_Jump        : int = 2;
 private var state_Fall        : int = 3;
 private var state_Crouch    : int = 4;
 
 //--------------------------
 //Animation Variables
 //--------------------------
 private var currentAnimationState    : int =    state_Idle;
 var anim                            : Animator;
 
 function Start(){
     anim = GetComponent("Animator");
 }
 
 function Update(){
 
 //---------------------------
 //Getting components section:
 //---------------------------
 
 var aniPlay = GetComponent("Animator");
 var controller : CharacterController = GetComponent(CharacterController);    //Gets/Imports the character controller component- NEEDS ONE CONNECTED!
 //----------End Of Section---------------
 
 //---------------------------------------------------
 //Character movement, crouch, dive, and jump section:
 //---------------------------------------------------
 
 if(controller.isGrounded){
     velocity = Vector3 (Input.GetAxis ("Horizontal"), 0, 0);    //Moves the character controller horizontally - CHECK: EDIT/PROJECT SETTINGS/INPUT
     
     //-----------
     //Idle
     //-----------
     
     if(velocity.x == 0 && !isCrouching && idleEnabled){
         isWalking = false;
         ChangeState(state_Idle);
     }
     
     //--------------
     //Movement Left
     //--------------
     
     if(velocity.x < 0){            //Walking animation left
         velocity *= walkSpeed;            //Applies walking speed
         ChangeState(state_Walk);    //Plays Walking animation left
         idleEnabled = false;
         isWalking = true;
     }
     else{
         idleEnabled = true;
         isWalking = false;
     }
     
     //---------------
     //Movement Right
     //---------------
     
     if(velocity.x > 0){            //Walking animation right
         velocity *= walkSpeed;    //Applies walking speed
         ChangeState(state_Walk);//Plays Walking animation right
         idleEnabled = false;
         isWalking = true;
     }
     else{
         idleEnabled = true;
         isWalking = false;
     }
     
     //--------------
     //The Jump Move
     //--------------
     
     if(Input.GetButton ("Jump") && jumpEnabled && !isCrouching){
         isJumping = true;
         crouchEnabled = false;
         velocity.y = jumpHeight;    //This causes the player to jump
         ChangeState(state_Jump);    //Plays jumping up animation
     }
     else if(!isJumping){
         crouchEnabled = true;
         jumpEnabled    = true;
         
         isCrouching = false;
         isJumping = false;
     }
     
 }
 
 //-----------------
 //Movement in air
 //-----------------
 
 if(!controller.isGrounded){
     velocity.x = Input.GetAxis("Horizontal");//This allows the player to move while in air/jumping
     velocity.x *= runSpeed;
 }
 
 //---------
 //Falling!
 //---------
 
 if(!controller.isGrounded && controller.velocity.y < 0){
     ChangeState(state_Fall);//Plays falling down animation
 }
 
 //-----------------
 //The crouch move
 //-----------------
 
 if(velocity.x == 0 && Input.GetAxis("Vertical") < 0 && controller.isGrounded && crouchEnabled && !isJumping){
     isCrouching = true;
     jumpEnabled = false;
     ChangeState(state_Crouch);//Plays crouching animation
 }
 else if(!isCrouching){
     crouchEnabled = true;
     jumpEnabled    = true;
     
     isCrouching = false;
     isJumping = false;
 }
 
 
 //-----------End Of Section----------------------
 
 //----------------------------------------------
 //Stores which direction the player is facing:
 //----------------------------------------------
 
 if(velocity.x < 0){    //Character facing left
     moveDirection = 0;
 }
 
 if(velocity.x > 0){    //Character facing right
     moveDirection = 1;
 }
 //---------End Of Storing Direction--------------
 
 //----------------------------
 //Controller Collision Center
 //----------------------------
 
 //--------------------------------------------------
 //Collide with roof (Above), aftger hit force down
 //--------------------------------------------------
 if(controller.collisionFlags == CollisionFlags.Above){
     velocity.y = 0;
     velocity.y -= afterHitForceDown;    //Applies downward force to player
 }
 //-----------End of Secction--------------------
 
 //---------------------------
 //Necessary Stuff
 //---------------------------
 velocity.y -= gravity * Time.deltaTime;        //Applies gravity
 controller.Move(velocity * Time.deltaTime);    //Moves the controller
 }
 
 //-----------------------
 //Change State Function
 //-----------------------
 
 function ChangeState(State : int){
 if (currentAnimationState == State)
         return;
  
         switch (State) {
  
                case state_Idle:
                 anim.SetInteger ("State", state_Idle);
                 break;
                 
             case state_Walk:
                 anim.SetInteger ("State", state_Walk);
                 break;
             
             case state_Jump:
                 anim.SetInteger ("State", state_Jump);
                 break;
             
             case state_Fall:
                 anim.SetInteger ("State", state_Fall);
             
             case state_Crouch:
                 anim.SetInteger ("State", state_Crouch);
                 break;
  
         }
 }