C # Connection Database

/*

           /*
Try            {                string constr = "Data source=user-20170228gj\\sqlexpress;initial catalog=db_zrmex;user=sa;pwd=123;"; /Database Connection field                SqlConnection conn = new SqlConnection (CONSTR);                Conn. Open ();                MessageBox.Show ("Connect database successfully!");            }            Catch            {                MessageBox.Show ("Failed to connect to database!");            }             */


Add App. Config file
/*

<?xml version= "1.0" encoding= "Utf-8"?>
<configuration>
<connectionStrings>
<add name= "Constr" connectionstring= "Data source=user-20170228gj\sqlexpress;initial Catalog=db_zrmex;user=sa; pwd=123; "/>
</connectionStrings>
</configuration>

*/
            Try            {                stringConnStr = configurationmanager.connectionstrings["Constr"]. ToString ();//you need to add a reference system.configurationSqlConnection conn =NewSqlConnection (CONNSTR); Conn.                Open (); MessageBox.Show ("Connect to the database successfully!"); }            Catch{MessageBox.Show ("failed to connect to database!"); }

C # Connection Database