For vs. For Each vs. While in C#

Introduction 

I am often asked by some people/colleagues, "which loop is faster?" "Which loop has higher performance?" Etc. I have heard that the For loop is faster than the For...each loop but I have never tried it before. So, I decided to see how big the difference is among all the loops and which one is faster at looping through an array and a list in terms of speed and performance.

Let's start our journey to fin the best C# loop. For this exercise, I'll be creating a console application in Visual Studio 2017.  

First, I'm going to create one class called CustomStopwatch which helps to track the starting and ending times of loops. 

using System;  
using System.Diagnostics;  

namespace ConsoleApp2  
{  
    public class CustomStopwatch : Stopwatch  
    {  

        public DateTime? StartAt { get; private set; }  
        public DateTime? EndAt { get; private set; }  


        public void Start()  
        {  
            StartAt = DateTime.Now;  

            base.Start();  
        }  

        public void Stop()  
        {  
            EndAt = DateTime.Now;  

            base.Stop();  
        }  

        public void Reset()  
        {  
            StartAt = null;  
            EndAt = null;  

            base.Reset();  
        }  

        public void Restart()  
        {  
            StartAt = DateTime.Now;  
            EndAt = null;  

            base.Restart();  
        }  

    }  
}  

Now, it is time to write code in the Program.cs class. First, I'm going to implement a For loop on:

• a single integer.
• an array.
• a list.

using System;  
using System.Linq;  

namespace ConsoleApp2  
{  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            CustomStopwatch sw = new CustomStopwatch();  
            sw.Start();  
            for (int i = 0; i < 10000; i++) Console.WriteLine(i);  
            sw.Stop();  

            CustomStopwatch sw1 = new CustomStopwatch();  
            int[] array = Enumerable.Range(0, 10000).ToArray();  
            sw1.Start();  
            for (int i = 0; i < array.Length; i++) Console.WriteLine(array[i]);  
            sw1.Stop();  

            CustomStopwatch sw2 = new CustomStopwatch();  
            var arrList = array.ToList();  
            sw2.Start();  
            for (int i = 0; i < arrList.Count; i++) Console.WriteLine(arrList[i]);  
            sw2.Stop();  

            Console.WriteLine($"for Time elapsed: {sw.ElapsedMilliseconds} Milliseconds, StartAt: {sw.StartAt.Value}, EndAt: {sw.EndAt.Value}");  
            Console.WriteLine($"for on array Time elapsed: {sw1.ElapsedMilliseconds} Milliseconds, StartAt: {sw1.StartAt.Value}, EndAt: {sw1.EndAt.Value}");  
            Console.WriteLine($"for on list Time elapsed: {sw2.ElapsedMilliseconds} Milliseconds, StartAt: {sw2.StartAt.Value}, EndAt: {sw2.EndAt.Value}");  
            Console.ReadKey();  
        }  

    }  
}  

Let's run the script to see output and execution time in milliseconds.

As per my output, the For loop on the list is faster.  

Let's compare the For...each loop on the list and array.

using System;  
using System.Linq;  

namespace ConsoleApp2  
{  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            int[] array = Enumerable.Range(0, 10000).ToArray();  
            var arrList = array.ToList();  

            CustomStopwatch sw1 = new CustomStopwatch();  
            sw1.Start();  
            foreach (var arr in array) Console.WriteLine(arr);  
            sw1.Stop();  

            CustomStopwatch sw2 = new CustomStopwatch();  
            sw2.Start();  
            foreach (var arr in arrList) Console.WriteLine(arr);  
            sw2.Stop();  

            Console.Clear();  
            Console.WriteLine($"for each on array Time elapsed: {sw1.ElapsedMilliseconds} Milliseconds, StartAt: {sw1.StartAt.Value}, EndAt: {sw1.EndAt.Value}");  
            Console.WriteLine($"for each on list Time elapsed: {sw2.ElapsedMilliseconds} Milliseconds, StartAt: {sw2.StartAt.Value}, EndAt: {sw2.EndAt.Value}");  
            Console.ReadKey();  
        }  
    }  
}  

Let's run to see output and execution time in milliseconds.  

Here, the For...each loop on the list is faster. 

Let's compare the While loop on the list and an array.

using System;  
using System.Linq;  

namespace ConsoleApp2  
{  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            int[] array = Enumerable.Range(0, 10000).ToArray();  
            var arrList = array.ToList();  

            CustomStopwatch sw1 = new CustomStopwatch();  
            sw1.Start();  
            int i = 0;  
            while (i != array.Length) Console.WriteLine(array[i++]);  
            sw1.Stop();  

            CustomStopwatch sw2 = new CustomStopwatch();  
            sw2.Start();  
            i = 0;  
            while (i != arrList.Count) Console.WriteLine(arrList[i++]);  
            sw2.Stop();  

            Console.Clear();  
            Console.WriteLine($"while on array Time elapsed: {sw1.ElapsedMilliseconds} Milliseconds, StartAt: {sw1.StartAt.Value}, EndAt: {sw1.EndAt.Value}");  
            Console.WriteLine($"while on list Time elapsed: {sw2.ElapsedMilliseconds} Milliseconds, StartAt: {sw2.StartAt.Value}, EndAt: {sw2.EndAt.Value}");  
            Console.ReadKey();  
        }  
    }  
}  

And the output of While loop is as below.  

The While loop is faster at looping through the list.  

Conclusion  

This article covered a quick comparison of For, For...each, and While loops on arrays and lists. As I said before, an array is faster than a list, but, as per my observation (in terms of iteration), a list is faster, as we can see in the outputs. I think it depends on the data and the way you use the data. My personal suggestion is that we should use a list instead of an array for the below reasons.

• In an array, we need to know the array's size, and we can't change the array's size (we have the Resize() method but it will change the reference) where a list can grow after it's created.
• In a list, we don't need to worry about the list's size or  an 'index out of bounds' exception.
• A list provides lots of helpful methods like Add, Find, etc.
• Lists are easy to read. 

Please give your valuable feedback/comments/questions about this article below. Please let me know how you like and understand this article and how I could improve it.