Counter in foreach loop in C#

It depends what you mean by “it”. The iterator knows what index it’s reached, yes – in the case of a List<T> or an array. But there’s no general index within IEnumerator<T>. Whether it’s iterating over an indexed collection or not is up to the implementation. Plenty of collections don’t support direct indexing.

(In fact, foreach doesn’t always use an iterator at all. If the compile-time type of the collection is an array, the compiler will iterate over it using array[0], array[1] etc. Likewise the collection can have a method called GetEnumerator() which returns a type with the appropriate members, but without any implementation of IEnumerable/IEnumerator in sight.)

Options for maintaining an index:

• Use a for loop
• Use a separate variable

• Use a projection which projects each item to an index/value pair, e.g.

   foreach (var x in list.Select((value, index) => new { value, index }))
   {
       // Use x.value and x.index in here
   }
  

• Use my SmartEnumerable class which is a little bit like the previous option

All but the first of these options will work whether or not the collection is naturally indexed.