Sql connection-string for localhost server

I am newbie in this .NET and please don't mind in answering my simple question. I am trying to write a windows application, where in I am using a localhost SQLserver for database.

I need to know what is the exact connection string for my localhost, if my server name looks like as below:

Data Source=HARIHARAN-PC\SQLEXPRESS;Initial Catalog=master;Integrated Security=True

should i need to give this same as connection string, or is something wrong in this syntax.

whn i try to open my connection. I am seeing error in opening connection.

How the format of connection string should be? any one please guide me.

I tried like this :

 private void button1_Click(object sender, EventArgs e)
    {
        string str = "Data Source=HARIHARAN-PC\SQLEXPRESS;Initial Catalog=master;Integrated Security=True" ; 
        SqlConnection con = new SqlConnection(str);
        SqlCommand cmd = new SqlCommand();
        SqlDataReader r;

        cmd.CommandText = "SELECT * from Table1";
        cmd.CommandType = CommandType.Text;
        cmd.Connection = con;

        con.Open();

        r = cmd.ExecuteReader();

        con.Close();


    }

This code errors out at con.Open();

Using the default instance (i.e., MSSQLSERVER, use the DOT (.))

<add name="CONNECTION_STRING_NAME" connectionString="Data Source=.;Initial Catalog=DATABASE_NAME;Integrated Security=True;" />

Choose a database name in Initial Catalog

Data Source=HARIHARAN-PC\SQLEXPRESS;Initial Catalog=your database name;Integrated Security=True" ;

see more

You can also use Dot(.) for local key i.e;

Data Source=.\SQLEXPRESS;Initial Catalog=master;Integrated Security=True

If you have the default server instance i.e. MSSQLSERVER, then just use dot for Data Source.

Data Source=.;Initial Catalog=master;Integrated Security=True

Do You have Internal Connection or External Connection. If you did Internal Connection then try this:

"Data Source=.\SQLEXPRESS;AttachDbFilename="Your PAth .mdf";Integrated Security=True;User Instance=True";