It's generally a bad idea to hard code such stuff in your application. Normally, application settings and connection strings are placed in the application's configuration file (in the ConnectionStrings section). Just like with all strings, you could build your connectionstring from dynamic parts (variables, settings, etc.) and then pass that generated connectionstring to the SqlConnection constructor. Again, to make those separate parts configurable without hard coding them in your application, you might want to add them to your application's configuration file (in the AppSettings section). But IMHO this is an overly complex solution in most scenarios. Putting the entire connectionstring in the ConnectionStrings section is more straightforward (and more flexible). Anyway, again, to make your application configurable, you might use your application's configuration file (App.config or Web.config), you need to add a reference to System.Configuration in your project's .NET Framework dependencies and use the AppSettings and ConnectionStrings properties of the System.Configuration.ConfigurationManager class. (Of course, there are more ways to make your application configurable. But using the application configuration file is one of the most straightforward solutions.) Courtesy: Stack Overflow
