Connection string for windows application

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SQL-Server-2005

C#3.0

C#

, +

Error Occurs while connecting to the sql server.
I have windows application with sql server as my Database. I want deploy this at client side.
i want make the connection string that will connect my database to my application after installation of my sotware.
I have two connection string one which will connect my DBConnect

public DBConnect()
       {
           //connectionString = System.Configuration.ConfigurationManager.AppSettings["ConnectionString"];
           connectionString = @"Data Source=.\SQLEXPRESS;AttachDbFilename=" + Application.StartupPath + "\\SiteManagement.mdf;Integrated Security=True;UserInstance=True";
       }

while second will connect my Sql connection string.
sqlConnection1.ConnectionString = @"Data Source=.\SQLEXPRESS;AttachDbFilename=" + Application.StartupPath + "\\SiteManagement.mdf;Integrated Security=True;User Instance=True";