>Update
>But you may want to test
>
>(1) pattern == null
>(2) pattern.Length == 0 ( division by zero)
>
>>

>> /// <summary>
>>      /// Occurs function
>>      /// </summary>
>>      /// <param name="source"></param>
>>      /// <param name="pattern"></param>
>>      /// <returns></returns>
>>      public static Int32 Occurs(this String source, char pattern)
>>      {
>>         return source.Split(pattern).Length - 1;
>>      }
>>
>>      public static Int32 Occurs(this String source, String pattern)
>>      {
>>         return (source.Length - source.Replace(pattern, "").Length)/pattern.Length;
>>      }

Good point, I guess I'll add these two checks in both and return 0 in these cases.

/// <summary>
      /// Occurs function
      /// </summary>
      /// <param name="source"></param>
      /// <param name="pattern"></param>
      /// <returns></returns>
      public static Int32 Occurs(this String source, char pattern)
      {
         if (null==pattern)
            return 0;
         return source.Split(pattern).Length - 1;
      }

      public static Int32 Occurs(this String source, String pattern)
      {
         if (String.IsNullOrEmpty(pattern))
            return 0;
         return (source.Length - source.Replace(pattern, "").Length)/pattern.Length;
      }