BurgZergArcade RPG - Base Character script errors[List]

Base Character.cs ;

 using UnityEngine;
 using System.Collections;
 using System;
 
 public class BaseCharacter : MonoBehaviour {
     private string _name;
     private int _level;
     private uint _freeExp;
 
 private Attribute[] _primaryAttribute;
 private Vital[] _vital;
 private Skill[] _skill;
 
 public void Awake() {
     _name = string.Empty;
     _level = 0;
     _freeExp = 0;
 
     _primaryAttribute = new Attribute[Enum.GetValues(typeof(AttributeName)).Lenght];
     _vital = new Vital[Enum.GetValues(typeof(VitalName)).Lenght];
     _skill = new Skill[Enum.GetValues(typeof(SkillName)).Lenght];
 
     SetupPrimaryAttributes();
     SetupVitals();
     SetupSkills();
 }
 
 public string Name {
     get{ return _name; }
     set { _name = value; }
 }
 
 public int Level {
     get{ return _level; }
     set{ _level = value; }
 }
 
 public uint FreeExp {
     get{ return _freeExp; }
     set{ _freeExp = value; }
 }
 
 public void AddExp(uint exp) {
     _freeExp += exp;
 
     CalculateLevel();
 }
 
 
 //take avg of all of the players skills and assign that as the player level
 public void CalculateLevel() {
 }
 
 
 private void SetupPrimaryAttributes() {
     for(int cnt = 0; cnt < _primaryAttribute.Lenght; cnt++) {
        _primaryAttribute[cnt] = new Attribute();
     }
 }
 
 private void SetupVitals() {
     for(int cnt = 0; cnt < _vital.Lenght; cnt++) {
        _vital[cnt] = new Vital();
     }
 }
 
 private void SetupSkills() {
     for(int cnt = 0; cnt < _skill.Lenght; cnt++) {
        _skill[cnt] = new Skill();
     }
 }
 
 public Attribute GetPrimaryAttribute(int index) {
     return _primaryAttribute[index];
 }
 
 public Vital GetVital(int index) {
     return _vital[index];
 }
 
 public Skill GetSkill(int index) {
     return _skill[index];
 }
 
 private void SetupVitalModifiers() {
     //health
     GetVital((int)VitalName.Health).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Constitution), .5f));
     //energy
     GetVital((int)VitalName.Energy).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Constitution), 1));
     //mana
     GetVital((int)VitalName.Mana).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Willpower), 1));
 }
 
 private void SetupSkillModifiers() {
     //melee offence
     GetSkill((int)SkillName.Melee_Offence).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Might), .33f));
     GetSkill((int)SkillName.Melee_Offence).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Nimbleness), .33f));
     //melee defence
     GetSkill((int)SkillName.Melee_Defence).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Speed), .33f));
     GetSkill((int)SkillName.Melee_Defence).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Constitution), .33f));
     //magic offence
     GetSkill((int)SkillName.Magic_Offence).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Concentration), .33f));
     GetSkill((int)SkillName.Magic_Offence).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Willpower), .33f));
     //magic defence
     GetSkill((int)SkillName.Magic_Defence).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Concentration), .33f));
     GetSkill((int)SkillName.Magic_Defence).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Willpower), .33f));
     //ranged offence
     GetSkill((int)SkillName.Ranged_Offence).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Concentration), .33f));
     GetSkill((int)SkillName.Ranged_Offence).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Speed), .33f));
     //ranged defence
     GetSkill((int)SkillName.Ranged_Defence).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Speed), .33f));
     GetSkill((int)SkillName.Ranged_Defence).AddModifier(new ModifyingAttribute(GetPrimaryAttribute((int)AttributeName.Nimbleness), .33f));
 }   
 
 public void StatUpdate() {
     for(int cnt = 0; cnt < _vital.Length; cnt++)
        _vital[cnt].Update();
 
     for(int cnt = 0; cnt < _skill.Length; cnt++)
        _skill[cnt].Update();
 }
 
 }

ModifiedStat.cs

 using System.Collections.Generic;
 
 public class ModifiedStat : BaseStat {
 
 private List _mods; //A list of Attributes that modify this stat
 
 private int _modValue; //The amount added to the baseValue from the modifiers
 public ModifiedStat() {
     _mods = new List<ModifyingAttribute>();
     _modValue = 0;
 }
 
 public void AddModifier( ModifyingAttribute mod) {
     _mods.Add(mod);
 }
 
 private void CalculateModValue() {
     _modValue = 0;
 
     if(_mods.Count > 0)
        foreach(ModifyingAttribute att in _mods)
          _modValue += (int)(att.attribute.AdjustedBaseValue * att.ratio);
 }
 
 public new int AdjustedBaseValue {
        get{ return BaseValue + BuffValue + _modValue; }
 }
 
 public void Update() {
     CalculateModValue();
 }
 
 
 }
 
 public struct ModifyingAttribute { public Attribute attribute; public float ratio;
 public ModifyingAttribute(Attribute att, float rat) {
     attribute = att;
     ratio = rat;
 }
 
 
 }

BaseStat.cs;

 public class BaseStat {
     private int _baseValue;    //the bae valie of this stat
     private int _buffValue;    //the amount of the buff to this stat
     private int _expToLevel;    //the total amount of exp needed to raise this skill
     private    float _levelModifier;    //the modifier applied to the exp needed to raise the skill
     
     public BaseStat() {
         _baseValue = 0;
         _buffValue = 0;
         _levelModifier = 1.1f;
         _expToLevel = 100;
     }
     
 #region Basic Setters and Getters
     //Basic Setters and Getters
     public int BaseValue {
         get{ return _baseValue; }
         set{ _baseValue = value; }
     }
     
     public int BuffValue {
         get{ return _buffValue; }
         set{ _buffValue = value; }
     }
     
     public int ExpToLevel {
         get{ return _expToLevel; }
         set{ _expToLevel = value; }
     }
     
     public float LevelModifier {
         get{ return _levelModifier; }
         set{ _levelModifier = value; }
     }
 #endregion
 
     private int CalculateExpToLevel() {
         return (int)(_expToLevel * _levelModifier);
     }
     
     public void LevelUp() {
         _expToLevel = CalculateExpToLevel();
         _baseValue++;
     }
     
     public int AdjustedBaseValue {
         get{ return _baseValue + _buffValue; }
     }
 }

ERROR

 Assets/Scripts/Character Classes/ModifiedStat.cs(5,9): error CS0246: The type or namespace name `List' could not be found. Are you missing a using directive or an assembly reference?

Please Help :(