哈希算法GetHashCode()起什么效果？

例如下面的例子GetHashCode()起什么作用：using System;
struct A
{
   public int count;
}class B
{
   public int number;
}class C
{
   public int integer=0;
   public override bool Equals(object obj)
   {
      C c=obj as C;
      if (c!=null)
         return this.integer==c.integer;
      else
         return false;
   }
   public override int GetHashCode()
   {
      return 2^integer;
   }
}哈希算法到底是什么？