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string path inside a directory of WPF c# solution

I created a directory inside my WPF solution called Sounds and it holds sound files.(For example: mySound.wav).
Inside my code I use a List and there I have to add to those strings that relate to the sound files. In the beginning I used #"C:..." but I want it to be something like "UNIVERSAL" path. I tried using: "\Sounds\mySound.wav" but it generates an error.
The lines that I use there this directory are:
myList.Add("\Sounds\11000_0.2s.wav");//Error
using (WaveFileReader reader = new WaveFileReader(sourceFile))
where sourceFile is a string which express a path of the file.

Make sure that you check CopyToOutputDir in the properties of the soundfile, that will make sure the file is copied to the location you program runs from.
Also don't use single backslashes in the path since its an escape character.
Instead, do one of the following things:
Use a verbatim string:
#"Sounds\11000_0.2s.wav"
Escape the escape char:
"Sounds\\11000_0.2s.wav"
Use forward slashes:
"Sounds/11000_0.2s.wav"
For more information on string literals check msdn.

You either need to escape the / in the string or add the string literal indicator # at the beginning of the string.
Escape example:
var myFilePath = "c:\\Temp\\MyFile.txt";
String literal example:
var myFilePath = #"c:\Temp\MyFile.txt";

Directory.GetFiles alters string path

Using System.IO, I tried the following code:
string[] files = Directory.GetFiles("\\folder\\folder_2\\folder_3");
And got the following exception:
"System.IO.DirectoryNotFoundException - It was not possible to locate part of the path 'C:\folder\folder_2\folder_3)' "
I don't know why "c:\" was added to the original string, and I can't seem to keep the method from doing so. What am I doing wrong?
Any help is much appreciated.

A backslash (\) at the start of a path makes it an absolute path. Remove the first \ if you want a relative path:
string[] files = Directory.GetFiles("folder\\folder_2\\folder_3");

You need to escape each of the beginning backslashes in your path, you only escaped a single slash. Use either correct escaping:
string[] files = Directory.GetFiles("\\\\folder\\folder_2\\folder_3");
Or you can use a verbatim string literal:
string[] files = Directory.GetFiles(#"\\folder\folder_2\folder_3");
Full explanation found in MSDN Documentation

In addition to the answers provided, you could use verbatim string literals, which will pass the string exactly without the need for escaping with all the messy backslashes.
In your case this would be
string[] files = Directory.GetFiles(#"folder\folder_2\folder_3");
Notice that the # is outside of quotes, but stuck to the opening quotes, this tells C# to use it, (pardon the pun) literally. The syntax highlighting for this kind of string will also change in Visual Studio, just FYI.
edit: saw a comment by another user advising you to use the #, it's the same thing. Sorry did not see this earlier.
Read about them here at MSDN

Trim characters from a string

I need to trim a substring from a string, if that substring exists.
Specifically, if the string is "MainGUI.exe", then I need it to become "MainGUI", by trimming ".exe" from the string.
I tried this:
String line = "MainGUI.exe";
char[] exe = {'e', 'x', 'e', '.'};
line.TrimEnd(exe);
This gives me the correct answer for "MainGui.exe", but for something like "MainGUIe.exe" it doesn’t work, giving me "MainGUI" instead of "MainGUIe".
I am using C#. Thanks for the help!

Use the Path static class in System.IO namespace, it lets you strip extensions and directories from file names easily. You can also use it to get the extension, full path, etc. It's a very handy class and well worth looking into.
var filename = Path.GetFileNameWithoutExtension(line);
Gives you "MainGui", this is, of course, assuming you want to trim any file extension or you know your file is always going to be a .exe file, if you want to only trim extensions off of .exe files, however, and leave it on others. You can test first, either by using String.EndsWith() or by using the Path.GetExtension() method.

I would use Path.GetFileNameWithoutExtension instead of string manipulation to handle this.
string line = “MainGUI.exe”;
string fileWithoutExtension = Path.GetFileNameWithoutExtension(line);
If you only want to strip off the extension if it's .exe, you can check for that as well. The following will only strip off extensions of .exe, but leave all other extensions intact:
string ext = Path.GetExtension(line).ToLower();
string fileWithoutExtension = ext == ".exe"
? Path.GetFileNameWithoutExtension(line)
: line;

The Path class has a GetFileNameWithoutExtension.

If you are always trimming ".exe" you can trim the last 4 characters off regardless of the rest of the string.
line.Substring(0, line.Length - ".exe".Length);

string line = "MainGUI.exe";
if (line.EndsWith(".exe"))
line = line.Substring(0, line.Length - 4);

As no file extension has a dot (.) within it, you are safe to use this:
String line = "MainGUI.exe";
line = line.Substring(0, line.LastIndexOf('.'));

What actually happen behind Path.Combine

I have :
string Combine = Path.Combine("shree\\", "file1.txt");
string Combine1 = Path.Combine("shree", "file1.txt");
Both gives same result :
shree\file1.txt
What actually happen behind Path.Combine?Which is the best coding practice to do this.please clear my vision.Thanks.

If the first path (shree or shree\\) does not end with a valid separator character (e.g. DirectorySeparatorChar) it is appended to the path before concatenation.
So
string path1 = "shree";
string path2 = "file1.txt";
string combined = Path.Combine(path1, path2);
will result in "shree\file1.txt", while
string path1 = "shree\\";
already contains a valid separator character, so the Combine method will not add another one.
Here you typed two slashes in the string variable (path1). The first one just acts as an escape character for the second one. This is the same as using a verbatim string literal.
string path1 = #"shree\";
More information on the Combine method can be found on MSDN:
http://msdn.microsoft.com/en-us/library/fyy7a5kt.aspx

Use the second one. This way you don't care about what is the directory separator.

What actually happen behind Path.Combine?
It builds you a path... so it's doesn't matter what of those two you will use. but those \\ are redundant.
If you're interested with micro optimization, create a test which of the two is faster.

Conversion to a double-escaped string

In C#, I have a filename that needs to converted to be double-escaped (because I feed this string into a regex).
In other words, if I have:
FileInfo file = new FileInfo(#"c:\windows\foo.txt");
string fileName = file.FullName;
fileName is: c:\\\\windows\\\\foo.txt
But I need to convert this to have sequences of two literal backslashes \\ in the fileName.
fileName needs to be #"c:\\\\windows\\\\foo.txt", or "c:\\\\\\\\windows\\\\\\\\foo.txt".
Is there an easy way to make this conversion?

I Think you're looking for Regex.Escape
Regex.Escape(#"c:\test.txt") == #"C:\\Test\.txt"
notice how it also escapes '.'

simplest without resorting to regex for this part:
string fileName = file.FullName.Replace(#"\", #"\\\\");
based on OP, but I think you really want this:
string fileName = file.FullName.Replace(#"\", #"\\");
That being said, I can't see how you want to use it... it shouldn't need escaping at all... maybe you should post more code?