C# - Create a file and compute its hash at the same time

writeandhash.cs

using System;
using System.IO;
using System.Security.Cryptography;

namespace HashDemo
{
    class Program
    {
        public static void Main (string[] args)
        {
            string filename = Path.GetTempFileName();
            SHA256 hash = SHA256.Create();

            string digest;
            string expected_digest = "BA7816BF8F01CFEA414140DE5DAE2223B00361A396177A9CB410FF61F20015AD";

            using (Stream stream = new FileStream(filename, FileMode.Create, FileAccess.Write)) {
                using (CryptoStream cs = new CryptoStream(stream, hash, CryptoStreamMode.Write)){

                    // 'abc'
                    cs.Write(new byte[] {0x61, 0x62, 0x63}, 0, 3);
                    cs.FlushFinalBlock();

                    digest = BitConverter.ToString (hash.Hash).Replace ("-", "");

                    if (expected_digest != digest) {
                        Console.WriteLine ("Something has gone wrong...");
                    }
                    Console.WriteLine(digest);
                }

            }
        }
    }
}