Example:

using System;
using System.IO;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main()
        {
            byte[] b1 = { 10, 20, 24, 13, 15, 17 };
            byte[] b2 = new byte[6];

            byte large = 0;
            FileStream f1;
            f1 = new FileStream("abc.txt", FileMode.Create, FileAccess.Write);

            f1.Write(b1,0,6);
            f1.Close();

            f1 = new FileStream("abc.txt", FileMode.Open, FileAccess.Read);

            f1.Read(b2, 0, 6);

            large = b2[0];
            for (int i = 1; i < b2.Length; i++)
            { 
                if (large < b2[i])
                    large = b2[i];
            }

            Console.WriteLine("Largest Item is : " + large);
            f1.Close();
        }
    }
}

Output

Largest Item is : 24

In this program, we are performing read and write operation into file and find largest element from file.

In above program, we need to remember, when we use "FileStream" class then we need to include System.IO namespace in the program.