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How do I write a backslash (\) in a string?

I want to write something like this C:\Users\UserName\Documents\Tasks in a textbox:
txtPath.Text = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)+"\Tasks";
I get the error:
Unrecognized escape sequence.
How do I write a backslash in a string?

The backslash ("\") character is a special escape character used to indicate other special characters such as new lines (\n), tabs (\t), or quotation marks (\").
If you want to include a backslash character itself, you need two backslashes or use the # verbatim string:
var s = "\\Tasks";
// or
var s = #"\Tasks";
Read the MSDN documentation/C# Specification which discusses the characters that are escaped using the backslash character and the use of the verbatim string literal.
Generally speaking, most C# .NET developers tend to favour using the # verbatim strings when building file/folder paths since it saves them from having to write double backslashes all the time and they can directly copy/paste the path, so I would suggest that you get in the habit of doing the same.
That all said, in this case, I would actually recommend you use the Path.Combine utility method as in #lordkain's answer as then you don't need to worry about whether backslashes are already included in the paths and accidentally doubling-up the slashes or omitting them altogether when combining parts of paths.

To escape the backslash, simply use 2 of them, like this:
\\
If you need to escape other things, this may be helpful..

There is a special function made for this Path.Combine()
var folder = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
var fullpath = path.Combine(folder,"Tasks");

Just escape the "\" by using + "\\Tasks" or use a verbatim string like #"\Tasks"

txtPath.Text = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)+"\\\Tasks";
Put a double backslash instead of a single backslash...

even though this post is quite old I tried something that worked for my case .
I wanted to create a string variable with the value below:
21541_12_1_13\":null
so my approach was like that:
build the string using verbatim
string substring = #"21541_12_1_13\"":null";
and then remove the unwanted backslashes using Remove function
string newsubstring = substring.Remove(13, 1);
Hope that helps.
Cheers

C#, escape double quote not working as expected

I'm trying to escape quotes in an xpath string like so:
var mktCapNode = htmlDoc.DocumentNode.SelectSingleNode("//*[#id=""yfs_j10_a""]");
The actual string I want passed is:
//*[#id="yfs_j10_a"]
This gives a compiler errors: ) expected and ; expected
I'm sure it's simple but I'm stumped. Any ideas?

You need to make this a verbatim string to use the "" as an escape
#"//*[#id=""yfs_j10_a""]"
For a normal string literal you need to use backslashes to escape the double quotes
"//*[#id=\"yfs_j10_a\"]"

Or use the escape char '\':
"//*[#id=\"yfs_j10_a\"]"

In C# the \ character is used to escape (see documentation).
This is different from VB where there are no escape characters except "" which escapes to ".
This means in C# you do not need vbCrLf to start a new line or vbTab to add a tab character to a string. Instead use "\r\n" and "\t".
You can also make the string a literal using the # character, but I do not think this works with the quotation mark.

Add the # prefix to your string.
#"//*[#id=""yfs_j10_a""]"
or escape the quotes with a \
"//*[#id=\"yfs_j10_a\"]"

C# Using Regular Expressions

The following works in vb.net, and basically only allows characters on a standard US Keyboard. Any other character pasted gets deleted. I use the following regular expression code:
"[^A-Za-z0-9\[\{\}\]`~!##$%\^&*\(\)_\-+=\\/:;'""<>,\.|? ]", "")
However when I try to use it in C# it won't work, I used '\' as a escape sequence. C# seems a bit different when it comes to escape sequences? Any help would be appreciated.

Prefix the string with #. That's it. From there you can use the regex string from VB as is (including doubling up on the " character).
// Note: exact same string you're using, only with a # verbatim prefix.
string regex = #"[^A-Za-z0-9\[\{\}\]`~!##$%\^&*\(\)_\-+=\\/:;'""<>,\.|? ]";
string crazy = "hĀečlĤlŁoźtƢhǣeǮrȡe";
Console.WriteLine(Regex.Replace(crazy, regex, ""));
Output:
hellothere

Prefix your string with "#" and prefix quotes within the string with "\".
I.e. this string
abc\def"hij
in C# would be encoded as
#"abc\def\"hij"

You need to escape your " character. Do this by putting a \ before your " character.
"[^A-Za-z0-9[{}]`~!##$%\^&*()_-+=\/:;'""<>,.|? ]"
should become
"[^A-Za-z0-9[{}]`~!##$%\^&*()_-+=\/:;'\"\"<>,.|? ]"
If you use the #prefix before this, it will treat the backslash literally instead of an escape character and you wont get the desired result.

Escape your characters:
"[^A-Za-z0-9[{}]`~!##$%\^&*()_-+=\\/:;'\"<>,.|? ]"
A good tool for regular expression design and testing (free) is:
http://www.radsoftware.com.au/regexdesigner/

You need to escape you regex for use in C#
[^A-Za-z0-9\[\{\}\]`~!##$%\^&*\(\)_\-+=\\/:;'\"<>,\.|? ]
Try this one!

How do you use this # in C#?

simpleSound = new SoundPlayer(#"c:\Windows\Media\chimes.wav");
Why and what is the # for?

It's a literal string. Instead of having to escape the "\" by putting two of them "\" the compiler interprets the string "as is".
Say you wanted to print out the following text to the screen: "Hello \t world".
If you were to just do Console.WriteLine("Hello \t world"), then your output would be:
Hello world
notice the tab. That's because \t is interperted as a tab. If you use the literal though, like this:
Console.WriteLine(#"Hello \t world")
then your output would be:
"Hello \t world"

The # sign before a string means to treat the backslash as a normal character rather than the start of a special character (such as newline).

It identifies a string literal. It allows you to have the special character \ in the string without escaping it.

It is a verbatim string. A verbatim string allows you to include special characters like \, " etc. without using the escape sequence.

Another usage of # is that you can put it in front of a keyword, if you want to use a keyword as a variable name (even if it's not a good idea). Example:
public int #object = 1;

Defining the # symbol prior to the assigning a string value will prevent the need for doubling the backslash (\) in C#. The at symbol (#) simply ignores escape characters.

"c:\\my\\file.txt" could be done as #"c:\my\file.txt"
This means your \n and \t or whatever it is will also not be processed.

alternate way of specifying string path to variable in C#

Is there another way of assigning string path to variable aside from this:
strPath = #"C:\Myfile.txt";
is there another way instead using "#" sign in the string path.
thanks.

You can escape it:
var myPath = "C:\\MyFile.txt"

Do you mean another way of escaping the backslashes?
The # sign at the start means that the string is treated as a verbatim string literal, and simple escape sequences such as \n or \t are ignored.
If you don't put the # at the start it is not verbatim, and escape sequences are parsed. If you want to ignore an individual escape sequence you can precede it with a single backslash and it will be ignored.
The reason you would use it in a path such as your example is so that you don't have to escape each individual backslash as you would if you didn't put the # at the start:
strPath = "C:\\Myfile.txt";

You can use forward slashes and it'll work fine on Windows and no escaping needed.
strPath = "C:/Myfile.txt";

You can use Unicode Escape Sequences....
string strPath = "C:\u005CMyfile.txt";

string path = Path.Combine("C:", "myfile.txt");