Difference Between IEnumerable and List in C#

IEnumerable :- IEnumerable is an Interface presents in System.Collections namespace and it is used for collection of items to be loop through each items one at a time.
In simple words we can say that the collections which implemets the IEnumerable Interface can be loop through Foreach loop.
IEnumerable is a Read Only Interface it means if you want to add or remove the items from IEnumerable you can not do that.

It has enumrated data means it gets data items from Interface one by one.
If you have a situation where you do not want to add and modify the collection items and You need to use items one by one then IEnumerable is the best to use.
Due to deffered execution it is much faster than list because in deffered execution it only gets data when it needed.

List :- List is a Collection Class presents in System.Collections namespace and It is collection of Items and we can access those items using the indexes. List is mainly used where you want to frequently add or remove the items from collection.

In simple words we can say that List is like a dynamic array that is shrink and grows when we remove or add the items into it. We can direct access any items from List using the index of the List.

Below is the Tabular Representation of the Differences in IEnumerable and List.

Sr.No	IEnumerable	List
1	IEnumerable is an Interface and present in System.Collections Namespace.	List is a Class and present in System.Collections Namespace.
2	IEnumerable is Read Only means you can not Add or Remove the items.	List is not Read Only means you Add or Remove the items.
3	IEnumerable supports the deferred execution means items fetched only when they needed during iterations.	List do not supports the deferred execution means it creates a new List imediately in memory when it is called.
4	IEnumerable is used where u only need to enumerate data once.	List is used where u need to enumerate data multiple times.
5	Data gets one by one using Interface in in-memory .	Data is in-memory so faster for frequently used data.
6	It has better memory utilization for large set of data.	It has memory overhead in case of large set of data.
7	Direct Indexing is not supported by it.	It has full support for Direct Indexing.

Implementation details of IEnumerable and List

IEnumerable Example

                
internal class Program
    {
        static void Main(string[] args)
        {
            IEnumerable enumItems = new List() {11,34,67,86,39,71,55,89,98,104 };
            Console.WriteLine("Items of  enumItems:-");
            foreach (int item in enumItems)
            {
                Console.Write(item+ "  ");
            }
            int maxValueFromItems=enumItems.Max();
            Console.WriteLine();
            Console.WriteLine("Maximum values for an Item is :-"+maxValueFromItems);
            Console.ReadKey();
        }
    }

Output of the above program

                
 Items of  enumItems:- 11 34 67 86 39 71 55 89 98 104
 Maximum values for an Item is :-104

List Example

                
internal class Program
    {
        static void Main(string[] args)
        {
             List listItems = new List() {"I","Love","India","And","Indians" };
            Console.WriteLine("display of Items in List :-");
            foreach (var item in listItems)
            {
                Console.Write(item+ "  ");
            }
            int listCount= listItems.Count;
            Console.WriteLine();
            Console.WriteLine("Number of Items in List :-"+ listCount);
            Console.ReadKey();
        }
    }

Output of the above program

                
 display of Items in List :-
 I  Love India  And  Indians
 Number of Items in List :-5

When to use IEnumerable and When to use List

When you have limited memory resource and read only operations then you can use IEnumerable.
When you want to frequently accessing data and wants to ADD Remove and Update on data then you can choose List.