The connection string defines which database server you are using, where It resides, your user name and password and optionally the database name.

//for SQL server

string  constr=”server=.; database=dbemployee; uid=sa; pwd=;” ;

//for SQL Express

string  constr=”server=.sqlexpress; database=dbemployee; uid=sa; pwd=;” ;

.sqlexpress – server name on the computer

Dbemployee – name of database with which we are dealing

sa – System administrator, user responsible for login in database.

Pwd – password which is blank if not given to the database otherwise we have to mentioned if given at the time of database creation.

SqlConnection cn = new SqlConnection(@”Data Source=.SQLEXPRESS;AttachDbFilename=”+ Application .StartupPath +“\dbdemo.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True”);