using System;

public class Program

{

    public static void Main()

    {

        string basePath = @"C:\something";

        string fileName = "somefile.txt";

        string pathExtension = @"In\ARB";

        string archiveExtension = "archive";

        Console.WriteLine(GetFullPath(basePath, fileName, pathExtension, archiveExtension));

    }

    private static string GetFullPath(string basePath, string fileName, params string[] pathExtensions )

        {

            string fullPath = basePath.EndsWith(@"\") || basePath.EndsWith(@"/") ? basePath.Substring(0, basePath.Length - 1) : basePath;

​

            foreach (string pathExtension in pathExtensions)

            {

                string extension;

                extension = pathExtension.StartsWith(@"\") || pathExtension.StartsWith(@"/") ? pathExtension.Substring(1) : pathExtension;

                extension = extension.EndsWith(@"\") || extension.EndsWith(@"/") ? extension.Substring(0, extension.Length - 1) : extension;

                fullPath += $@"\{extension}";

            }       

​

            return $@"{fullPath}\{fileName}";

        }

}