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How can i make a relative path for my database to my "mainfolder" so i can run my project on another computer?

I created a database, I put it into my bin/debug folder, I made the connection with |DataDirectory|, relative path, and when I try to open the project on another pc it freezes.
string constr = #"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\estic.mdf;Integrated Security=True;Connect Timeout=30";

error in Connection String in C#

I am new to C#. I want to use my Microsoft SQL Server database file test.mdf in my output software in C#. In the past, I had just copied the connection string in Visual Studio like this :
Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\Home\Documents\test.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True
as you see the database file path is : C:\Users\Home\Documents\test.mdf;
When I create setup for my sofware in Visual Studio 2008, and install the software on another PC, it errors :
An attempt to atach an auto-named database for file C:\User\Home\Document\test.mdf failed ...
So I want to address the file with the installation folder path whith this :
string dir = Application.StartupPath + "\\" + "test.mdf";
but when I want to run program in Visual Studio 2008 it erros
string dir = Application.StartupPath + "\\" + "test.mdf";
SqlConnection con = new SqlConnection(#"Data Source=.\SQLEXPRESS;AttachDbFilename=" + dir + ";Integrated Security=True;Connect Timeout=30;User Instance=True");
Error 1 A field initializer cannot reference the non-static field,
method, or property
'phonebook.Form1.dir' C:\Users\Home\Documents\Visual Studio
2008\Projects\phonebook\phonebook\Form1.cs 25 95 phonebook
UPDATE
When I use
SqlConnection con = new SqlConnection(#"Data Source=.\SQLEXPRESS;AttachDbFilename="+ Application.StartupPath +" \\test.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");
it errors :
One or more files do not match the primary file of the database. If
you are attempting to attach a database, retry the operation with the
correct files. If this is an existing database, the file may be
corrupted and should be restored from a backup. Cannot open user
default database. Login failed. Login failed for user 'Home-PC\Home'.
While I have copied right test.mdf file there

As the error message says, you can't use the value of one instance field when initializing another. You probably don't want dir as a field anyway. Just move all of this into the body of the constructor... or ideally, only create your SqlConnection when you need it anyway. Don't use a single instance throughout your application, but go through a "create, use, dispose" cycle every time you need database access. (Ideally, don't do this in your GUI code, either...)

Access DB connected with local directory

Basically I want the connection of my Access DB always available, so if i move the folder project to another computer it has to keep working, without changing the folder path.
I'm working with Windows Forms in Visual Studio 2012.
conn.ConnectionString = #"Provider=Microsoft.Jet.OLEDB.4.0;Data source= Z:\Tempesta\Area Progetto\Area_Progetto_27_02_2014\Area_Progetto_DATA_MAGAZINE\Data_Magazine\Data_Magazine\DB\DataMG.mdb";
That's the code I have right now for the connection to the DB.

Try this
conn.ConnectionString = #"Provider=Microsoft.Jet.OLEDB.4.0; Data
Source=|DataDirectory|DataMG.mdb"

Connection string to access database in Program files

I am working on windows form which uses microsoft access database.
When the application will be installed, the database will be on this location
C:\Program Files (x86)\Amrit\trial\Database.
How can i make this work so that this application will linked to the database when installed in my computer.
Can somebody give me easy solution..
Currently my connection string looks like this..
string connString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\Users\\Amrit\\Desktop\\Database.accdb ;Persist Security Info=False;";
when i create setup file for appplication, the database will be in ProgramFiles/AmritCreations/AppName/Database.accdb

Just place your database and your application in the same directory and use this connectionString
string connString = "Provider=MICROSOFT.ACE.OLEDB.12.0; " +
"Data Source=|DataDirectory|/Database.accdb";
In times you're creating a Setup Project, try to place the database file and [yourProjectName].exe in the same directory.

Setting The Path of an db mdf file in local folder

How come The path I inserted in my Database Context is not working? Here's the code for my path
private string dbPath = #"TEST.MDF"
DataClasses1DataContext myDbContext = new DataClasses1DataContext(dbPath);
But when I run a query this gives me an error
An attempt to attach an auto-named database for file TEST.MDF failed. A database with the same name exists, or specified file cannot
be opened,
or it is located on UNC share.
And This is how My Folder looks like this
The mdf file is in the same location of my cs source code but the thing is they are not reading the path correctly.
my idea for this is that when I transfer to a diffrent pc I don't have to set up the paths again and again. are there any fix for this?

What about
private string dbPath = Application.StartupPath + "\\TEST.MDF";
But your Test.mdf isn't in the correct directory. Move it into \bin\Debug for this code to work.

Better you add your .mdf file in your project.. Add Existing Item=>Choose .mdf file from folder. After adding .mdf file in project, in Web.config or App.Config file connection string will be generate automatically and you can use that connection string to boot your store. Now as you build your project new .mdf file get copy into /bin/dubug folder and you dont need to write single line of code to connect your .mdf file.

Use this connection string :
SqlConnection connect = new SqlConnection("Data Source=(LocalDB)\\MSSQLLocalDB;AttachDbFilename="+ AppDomain.CurrentDomain.BaseDirectory.Substring(0, AppDomain.CurrentDomain.BaseDirectory.Length - 10)+"sampleDatabase.mdf;Integrated Security=True");
Because bin\Debug\ string length = 10, this is why we subtract 10; and now you can get the solution path address and can connect the MDF database.