MMO Like Experience System

The steps are:

Identify the experience needed for each level. Identify which level you're in based upon these thresholds. Subtract the top of the last level from your current xp amount to get the amount "in to this level" you are. Subtract the top of the last level from the top of this level to get the amount "of xp required this level" Divide "amount I'm in this level" by "amount required" to get "percent in this level".

Draw bar PERCENT wide. Where percent is the amount you just calculated and you multiply that percent by the width of a 100% bar. (If you are 20% in and the bar is 200 px wide, it would be 0.20 * 200 = 40 pixels wide)

 void Main()
 {
     XP xp = new XP(1300);
     Console.WriteLine("Our character starts at {0} xp and is level {1}.", xp.GetCurrentXp(), xp.GetCurrentLevel());
     Console.WriteLine("Now, we add 2000 xp.");
     xp.AddXp(2000);
     Console.WriteLine("Now, our character has {0} xp and is level {1}.", xp.GetCurrentXp(), xp.GetCurrentLevel());
     Console.WriteLine("Our character is {0}% in to his next level", xp.GetPercentInToLevel() * 100f);
 }
 
 public class XP {
     private int[] xpTargets = new int[] {0, 1000, 3000, 6000, 10000};
     private int currentXp = 0;
     
     public XP() { }
     public XP(int startingXp) { this.SetXp(startingXp); }
     
     public int GetCurrentXp(){
         return this.currentXp;
     }
     
     public int GetCurrentLevel(){
         for(int i = 0; i < (this.xpTargets.Length - 1) ; i++){ // Have to minus one since we're checking against "the next item" and there is no "next item" at the end of the list
             if(this.currentXp == this.xpTargets[i] || (this.currentXp > this.xpTargets[i] && this.currentXp < this.xpTargets[i + 1])){
             return (i + 1); // Since i is 0-based
             }
         }
         
         //If we're here, they're at the max level
         return this.xpTargets.Length;
     }
     
     public float GetPercentInToLevel(){
         int currentLevel = this.GetCurrentLevel();
         if(currentLevel == this.xpTargets.Length){
             // At max level, so 100%
             return 1.0f;
         }
         
         decimal xpInToLevel = (decimal)currentXp - (decimal)this.xpTargets[currentLevel - 1];
         decimal xpTopEnd = (decimal)this.xpTargets[currentLevel] - (decimal)this.xpTargets[currentLevel - 1];
         float percent = (float)xpInToLevel / (float)xpTopEnd;
         return percent;
     }
     
     public void SetXp(int newXp) {
         this.currentXp = newXp;
     }
     
     public bool AddXp(int xp){
         int startingLevel = this.GetCurrentLevel();
         this.currentXp += xp;
         if(this.GetCurrentLevel() == startingLevel) {
             return false; // We didn't level up with this xp
         }
         
         return true; // We leveled up.
     }
 }

Output:

 Our character starts at 1300 xp and is level 2.
 Now, we add 2000 xp.
 Now, our character has 3300 xp and is level 3.
 Our character is 10% in to his next level