IEnumerable vs List in C#

📌 Introduction

When learning C#, many beginners get confused between:

IEnumerable
List

Both are used to store collections of data.

But questions arise:

What is the difference?
When should I use IEnumerable?
When should I use List?
Which one is better?

In this article, we will understand everything in very simple words, with real examples and output.

🧠 What is IEnumerable?

IEnumerable is an interface in C#.

It is used for:

👉 Reading data

👉 Looping through data

👉 Returning collection of items

It allows only iteration (looping).

✅ Example of IEnumerable :

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        IEnumerable<string> names = new List<string>()
        {
            "Rahul",
            "Amit",
            "Neha"
        };

        foreach (var name in names)
        {
            Console.WriteLine(name);
        }
    }
}

Output

Rahul
Amit
Neha

🧠 What is List?

List<T> is a collection class.

It:

✔ Stores data

✔ Allows add/remove

✔ Allows indexing

✔ Allows modification

It is more powerful than IEnumerable.

✅ Example of List :

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List<string> names = new List<string>();

        names.Add("Rahul");
        names.Add("Amit");
        names.Add("Neha");

        names.Remove("Amit");

        foreach (var name in names)
        {
            Console.WriteLine(name);
        }
    }
}

Output

Rahul
Neha

🔍 Key Difference Between IEnumerable and List :

Feature	IEnumerable	List
Type	Interface	Class
Add/Remove	❌ No	✅ Yes
Modify Data	❌ No	✅ Yes
Index Access	❌ No	✅ Yes
Best For	Read-only data	Read + Write data

🎯 When Should You Use IEnumerable?

Use IEnumerable when:

✔ You only want to read data

✔ You don’t want data modification

✔ You are returning data from method

✔ You want better performance

Example:

public IEnumerable<string> GetNames()
{
    return new List<string> { "Rahul", "Amit" };
}

🎯 When Should You Use List?

Use List when:

✔ You need to add or remove items

✔ You need index access

✔ You need to modify collection

Example:

List<int> numbers = new List<int>();
numbers.Add(10);
numbers.Add(20);
numbers[0] = 50;

Real-Life Example

Imagine a Library:

IEnumerable → You can only read books.
List → You can add, remove, or edit books.

⚡ Performance Difference :

IEnumerable → Better for reading large data
List → Loads all data in memory

In real projects, we often return IEnumerable from methods to make code flexible.

🏁 Conclusion

In this article, we learned:

What is IEnumerable
What is List
Key differences
When to use each
Example with output
Interview tips

If you are beginner:

✔ Use List when modifying data

✔ Use IEnumerable when reading data