using System;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var header = new byte[]

        {

            0,

            1,

            2

        };

        var data = new byte[]

        {

            3,

            4,

            5,

            6

        };

        var checksum = new byte[]

        {

            7,

            0

        };

        var newArray = ConcatArrays(header, data, checksum);

        newArray.ToList().ForEach(i => Console.Write($"{i},"));

    }

​

    public static T[] ConcatArrays<T>(params T[][] list)

    {

        var result = new T[list.Sum(a => a.Length)];

        int offset = 0;

        for (int x = 0; x < list.Length; x++)

        {

            list[x].CopyTo(result, offset);

            offset += list[x].Length;

        }

​

        return result;

    }

}