Dotnet Interview Questions: IEnumerable and IEnumerator in C# with example

We will discuss here what is IEnumerable, IEnumerator, what are differences between them, where should we use IEnumerable and where to IEnumerator, once we will finish our discussion it will be clear, which one would be best for which situation and why, so let’s see it with example

To better understand we will create a list of age

List<int> ages = new List<int>();
ages.Add(10);
ages.Add(20);
ages.Add(30);
ages.Add(40);
ages.Add(50);

Now convert this list to IEnumerable

IEnumerable<int> age_IEnumerable = (IEnumerable<int>)ages;
foreach (int age in age_IEnumerable)
    Console.WriteLine(age);

There is nothing new, we used foreach here very straight forward, now let’s convert the ages into IEnumerator, there is a method GetEnumerator to convert a list into IEnumerator

IEnumerator<int> age_IEnumerator = ages.GetEnumerator();
while (age_IEnumerator.MoveNext())
    Console.WriteLine(age_IEnumerator.Current);

As you can see here we used while rather than foreach because foreach cannot be used with IEnumerator, but still there is nothing which can suggest us when should we use IEnumerable and where to IEnumerator.

Before we go further, we should know, IEnumerable uses IEnumerator internally also have a function GetEnumeratorto convert into IEnumerator, we should use IEnumerable because it make coding easier and clearer as we can see in above example.

Now let’s discuss the main difference, IEnumerable doesn’t remember the state, which row or record it is iterating while IEnumerator remember it and we are going to see this with example by creating method PrintUpto30 and PrintGreaterThan30

Let’s first check with IEnumerator

As we know IEnumerator persists state so once we will call PrintGreaterThan30 by passing
age_IEnumerator it will print the remaining list, here is the output: