I wish to configure a connection string in c#

Thank you Anil and Shanu, what you said is correct, but this being for an internal application i was asked to develop code for same. with this my end user(my supervisor) can access with dummy userid and passwords so that he need not change or modify connection string in app.config file always.

But its not good options to change Connection string by the end user.For security reasons dont do that.You can explain to your clients the disadvantages of doing this and it will be always good to have your connections string in Server computer webconfig file.For maintenace team or the admin who is incharge for the server they can alone change the Connection string if needed.

A connection string usually contains server and database information. Why anybody in this world would constitute it from user input? Can you tell us more about the requirement?