[c#] Connect to SQL Server 2012 Database with C# (Visual Studio 2012)

Evening all,

I'm trying to connect to a SQL Server 2012 database from C#. My connection settings when using SQL Server Management Studio are as below:-

Server Type:    Database Engine
Server Name:    Paul-PC\SQLEXPRESS
Authentication: Windows Authentication
Username:   Greyed out
Password:   Greyed out 

The name of the database I'm trying to connect to is "testDB".

Here's my code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace DatabaseConnection
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnConnect_Click(object sender, EventArgs e)
        {
            SqlConnection myConnection = new SqlConnection("server=localhost;" +
                                       "Trusted_Connection=yes;" +
                                       "database=testDB; " +
                                       "connection timeout=30");
            try
            {
                myConnection.Open();
                MessageBox.Show("Well done!");
            }
            catch(SqlException ex)
            {
               MessageBox.Show("You failed!" + ex.Message);
            }

        }
    }
}

Unfortunately, my code fails to connect with the following error:-

"You failed!A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections."

Any suggestions? SQL Server is running locally.

Note to under

connetionString =@"server=XXX;Trusted_Connection=yes;database=yourDB;";

Note: XXX = . OR .\SQLEXPRESS OR .\MSSQLSERVER OR (local)\SQLEXPRESS OR (localdb)\v11.0 &...

you can replace 'server' with 'Data Source'

too you can replace 'database' with 'Initial Catalog'

Sample:

 connetionString =@"server=.\SQLEXPRESS;Trusted_Connection=yes;Initial Catalog=books;";

Try:

SqlConnection myConnection = new SqlConnection("Database=testDB;Server=Paul-PC\\SQLEXPRESS;Integrated Security=True;connect timeout = 30");

Replacing server=localhost with server=.\SQLEXPRESS might do the job.

use this style

@"server=.\sqlexpress;"

I tested all the answers here, but for me, none worked. So I studied a bit the problem, and finally I found the connection string needed. To get this string, you do:
1. in you project name:
a. right click the project name,
b. click Add,
c. select SQL Server Database (obviously you can rename it as you wish).
Now the new desired database will be added to your project.
2. The database is visible in the Server Explorer window.
3. Left click the database name in the Server Explorer window; now check the Solution Explorer window, and you will find the "Connection String", along side with Provider, State, Type, Version.
4. Copy the connection string provided, and put it in the Page_Load method:

string source = @"Data Source=(LocalDB)\v11.0;AttachDbFilename=c:\x\x\documents\visual studio 2013\Projects\WebApplication3\WebApplication3\App_Data\Product.mdf;Integrated Security=True";
SqlConnection conn = new SqlConnection(source);
conn.Open();
//your code here;
conn.Close();

I renamed my database as Product. Also, in the "AttachDbFilename", you must replace "c:\x\x\documents\" with your path to the phisical address of the .mdf file.

It worked for me, but I must mention this method works for VS2012 and VS2013. Don't know about other versions.

In your connection string replace server=localhost with "server = Paul-PC\\SQLEXPRESS;"