C# using system.io not woking in my class but works in main

Question

I am working on an issue I do not remember ever having before. I am using VS2012 C#

When i add using System.IO; to my main program everything works fine

Answer 1

u have written in class, u cant write there. & also file.Exists() returns boolean value. u have to write something like this:

boolean a= File.Exists("bla");