if you are using Windows.Forms, you can certainly figure out the absolute path by combining your file path with 
System.Windows.Forms.Application.StartupPath
or
System.Windows.Forms.Application.ExecutablePath
or
System.Reflection.Assembly.GetExecutingAssembly().LocationBut a better way is to use System.IO.FileInfo class, for example
using System;
using System.IO; FileInfo fi = new FileInfo("TestFile.cs");
if (fi.Exists)
Console.WriteLine(fi.FullName);if you are using ASP.NET, try
String sFullPath = Server.MapPath("111.txt");