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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;
using System.IO;

namespace UseDLLs
{
    class Program
    {
        [DllImport("Search.dll")]
        public static extern string[] SearchForFile(string _dir, string _file, int _ArrayLength);

        static void Main(string[] args)
        {
            Console.WriteLine(SearchForFile(Directory.GetCurrentDirectory(), "Search.dll", 1)[0]);
        }
    }
}                    

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;
using System.IO;

namespace Search
{
    public class Class1
    {
        string[] FileArray;
        int i;

        public string[] SearchForFile(string _dir, string _file, int _ArrayLength)
        {
            i = 0;
            FileArray = new string[_ArrayLength];
            OpenDir(_dir, _file);
            return FileArray;
        }

        private void OpenDir(string _dir, string _file)
        {
            try
            {
                foreach (string file in Directory.GetFiles(_dir))
                {
                    if (file.Equals(_file))
                    {
                        FileArray[i] = file;
                        i++;
                    }
                }
                foreach (string dir2 in Directory.GetDirectories(_dir))
                {
                    OpenDir(dir2,_file);
                }
            }
            catch { }

        }
    }
}