Index out of range exception- I can't find the problem, Help!

Hi, I’ve been trying to make a game while following tutorials on how to do so, and now I came to the part where I had to implement things that don’t have a tutorial for them. Now I was trying some things out and somehow ended up with the following error:

ArgumentOutOfRangeException: Index is less than 0 or more than or equal to the list count.
Parameter name: index
0
System.Collections.ArrayList.ThrowNewArgumentOutOfRangeException (System.String name, System.Object actual, System.String message)
System.Collections.ArrayList.get_Item (Int32 index)
UnityScript.Lang.Array.get_Item (Int32 index)
AICar_Script.NavigateTowardsWaypoint () (at Assets/Scripts/Car Control/AICar_Script.js:135)
AICar_Script.Update () (at Assets/Scripts/Car Control/AICar_Script.js:65)

I’ve left the commentry from the tutorial in there, as I found it to be useful.
The error should have something to do with my waypoints for the script, which I assigned using gameobject.findwithtag. I went through the whole thing a couple times and can’t figure out why its giving me the error, so here’s the code, maybe you guys can figure it out :expressionless:

// ----------- CAR TUTORIAL SAMPLE PROJECT, ? Andrew Gotow 2009 -----------------

// Here's the basic AI driven car script described in my tutorial at www.gotow.net/andrew/blog.
// A Complete explaination of how this script works can be found at the link above, along
// with detailed instructions on how to write one of your own, and tips on what values to 
// assign to the script variables for it to work well for your application.

// Contact me at Maxwelldoggums@Gmail.com for more information.




// These variables allow the script to power the wheels of the car.
var FrontLeftWheel : WheelCollider;
var FrontRightWheel : WheelCollider;

// These variables are for the gears, the array is the list of ratios. The script
// uses the defined gear ratios to determine how much torque to apply to the wheels.
var GearRatio : float[];
var CurrentGear : int = 0;

// These variables are just for applying torque to the wheels and shifting gears.
// using the defined Max and Min Engine RPM, the script can determine what gear the
// car needs to be in.
var EngineTorque : float = 600.0;
var MaxEngineRPM : float = 5900.0;
var MinEngineRPM : float = 1000.0;
private var EngineRPM : float = 0.0;

// Here's all the variables for the AI, the waypoints are determined in the "GetWaypoints" function.
// the waypoint container is used to search for all the waypoints in the scene, and the current
// waypoint is used to determine which waypoint in the array the car is aiming for.
var waypointContainer : GameObject;
private var waypoints : Array;
private var currentWaypoint : int = 0;

// input steer and input torque are the values substituted out for the player input. The 
// "NavigateTowardsWaypoint" function determines values to use for these variables to move the car
// in the desired direction.
private var inputSteer : float = 0.0;
private var inputTorque : float = 0.0;

function Start () {

	//WaypointAssigner
	var container = GameObject.FindWithTag("WaypointContainer");
	var waypointContainer = container;

	// I usually alter the center of mass to make the car more stable. I'ts less likely to flip this way.
	rigidbody.centerOfMass.y = -1.5;
	
	// Call the function to determine the array of waypoints. This sets up the array of points by finding
	// transform components inside of a source container.
	GetWaypoints();
}

function Update () {
	
	// This is to limith the maximum speed of the car, adjusting the drag probably isn't the best way of doing it,
	// but it's easy, and it doesn't interfere with the physics processing.
	rigidbody.drag = rigidbody.velocity.magnitude / 250;
	
	// Call the funtion to determine the desired input values for the car. This essentially steers and
	// applies gas to the engine.
	NavigateTowardsWaypoint();
	
	// Compute the engine RPM based on the average RPM of the two wheels, then call the shift gear function
	EngineRPM = (FrontLeftWheel.rpm + FrontRightWheel.rpm)/2 * GearRatio[CurrentGear];
	ShiftGears();

	// set the audio pitch to the percentage of RPM to the maximum RPM plus one, this makes the sound play
	// up to twice it's pitch, where it will suddenly drop when it switches gears.
	audio.pitch = Mathf.Abs(EngineRPM / MaxEngineRPM) + 1.0 ;
	// this line is just to ensure that the pitch does not reach a value higher than is desired.
	if ( audio.pitch > 2.0 ) {
		audio.pitch = 2.0;
	}
	
	// finally, apply the values to the wheels.	The torque applied is divided by the current gear, and
	// multiplied by the calculated AI input variable.
	FrontLeftWheel.motorTorque = EngineTorque / GearRatio[CurrentGear] * inputTorque;
	FrontRightWheel.motorTorque = EngineTorque / GearRatio[CurrentGear] * inputTorque;
		
	// the steer angle is an arbitrary value multiplied by the calculated AI input.
	FrontLeftWheel.steerAngle = 10 * inputSteer;
	FrontRightWheel.steerAngle = 10 * inputSteer;
}

function ShiftGears() {
	// this funciton shifts the gears of the vehcile, it loops through all the gears, checking which will make
	// the engine RPM fall within the desired range. The gear is then set to this "appropriate" value.
	if ( EngineRPM >= MaxEngineRPM ) {
		var AppropriateGear : int = CurrentGear;
		
		for ( var i = 0; i < GearRatio.length; i ++ ) {
			if ( FrontLeftWheel.rpm * GearRatio *< MaxEngineRPM ) {*
  •  		AppropriateGear = i;*
    
  •  		break;*
    
  •  	}*
    
  •  }*
    
  •  CurrentGear = AppropriateGear;*
    
  • }*

  • if ( EngineRPM <= MinEngineRPM ) {*

  •  AppropriateGear = CurrentGear;*
    
  •  for ( var j = GearRatio.length-1; j >= 0; j -- ) {*
    

_ if ( FrontLeftWheel.rpm * GearRatio[j] > MinEngineRPM ) {_

  •  		AppropriateGear = j;*
    
  •  		break;*
    
  •  	}*
    
  •  }*
    
  •  CurrentGear = AppropriateGear;*
    
  • }*
    }

function GetWaypoints () {

  • // Now, this function basically takes the container object for the waypoints, then finds all of the transforms in it,*

  • // once it has the transforms, it checks to make sure it’s not the container, and adds them to the array of waypoints.*

  • var potentialWaypoints : Array = waypointContainer.GetComponentsInChildren( Transform );*

  • waypoints = new Array();*

  • for ( var potentialWaypoint : Transform in potentialWaypoints ) {*

  •  if ( potentialWaypoint != waypointContainer.transform ) {*
    
  •  	waypoints[ waypoints.length ] = potentialWaypoint;*
    
  •  }*
    
  • }*
    }

function NavigateTowardsWaypoint () {

  • // now we just find the relative position of the waypoint from the car transform,*

  • // that way we can determine how far to the left and right the waypoint is.*

  • var RelativeWaypointPosition : Vector3 = transform.InverseTransformPoint( Vector3(*

  •  										waypoints[currentWaypoint].position.x,* 
    
  •  										transform.position.y,* 
    
  •  										waypoints[currentWaypoint].position.z ) );*
    
  • // by dividing the horizontal position by the magnitude, we get a decimal percentage of the turn angle that we can use to drive the wheels*

  • inputSteer = RelativeWaypointPosition.x / RelativeWaypointPosition.magnitude;*

  • // now we do the same for torque, but make sure that it doesn’t apply any engine torque when going around a sharp turn…*

  • if ( Mathf.Abs( inputSteer ) < 1 ) {*

  •  inputTorque = RelativeWaypointPosition.z / RelativeWaypointPosition.magnitude - Mathf.Abs( inputSteer );*
    
  • }else{*

  •  inputTorque = 0.0;*
    
  • }*

  • // this just checks if the car’s position is near enough to a waypoint to count as passing it, if it is, then change the target waypoint to the*

  • // next in the list.*

  • if ( RelativeWaypointPosition.magnitude < 1 ) {*

  •  currentWaypoint ++;*
    
  •  if ( currentWaypoint >= waypoints.length ) {*
    
  •  	currentWaypoint = 0;*
    
  •  }*
    
  • }*

}

Your problem is quite simple. You have this public variable in your script:

var waypointContainer : GameObject;

BUT in your start function you create another local variable with the same name:

function Start () {
    var container = GameObject.FindWithTag("WaypointContainer");
    var waypointContainer = container;  // <<--- here

Just remove the var keyword so you would use the scripts variable instead of creating a local:

function Start () {
    var container = GameObject.FindWithTag("WaypointContainer");
    waypointContainer = container;

Run this in the debugger. It should stop on the very line when the offense occurs, and you should be able to read out the index, which would be less than zero or more than the length of the list. Also check that the length of the list is what you expect it to be.

That said, I don’t see where you actually allocate GearRatio, like GearRatio = new float[4]; or something like that. You need to do that or the array will be empty, causing such problems.

EDIT: it seems that I somehow assigned a container that was not in my scene onto my prefab, thus making it look like the one in my scene had been assigned, but when I unassign it there, the index out of range is fixed. However I seem to be doing something wrong still, because It does not automatically assign the container to the variable,
which it should do here(line 45 to 47):

//WaypointAssigner
var container = GameObject.FindWithTag("WaypointContainer");
var waypointContainer = container;

in which waypointContainer is declared here(line 35):

private var currentWaypoint : int = 0;

What am I doing wrong? o.o