Connection string in .Net

Connection string in .NET 3.5 (and above) config file
Do not use appsettings in web.config. Instead use the connectionStrings section in web.config.
<connectionStrings>
<add name="myConnectionString" connectionString="server=localhost;database=myDb;uid=myUser;password=myPass;" />
</connectionStrings>
To read the connection string into your code, use the ConfigurationManager class.
string connStr = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
Connection string in .NET 2.0 config file

In the appSettings location, add a key named whatever you like to reference your connection string to.

<appSettings>
<add key="myConnectionString" value="server=localhost;database=myDb;uid=myUser;password=myPass;" />
</appSettings>

To read the connection string from code, use the ConfigurationSettings class.

string connStr = ConfigurationSettings.AppSettings("myConnectionString");