How to write a method returning string value?

Question

Take below code for example, how can I return my first name? How to complete the code?

Thanks.

        public static string MyFirstName (string userID)
        {
            using (OdbcConnection Cn = new OdbcConnection(GlobalVariables.DatabaseConnectionString)) //Access database
            {
                Cn.Open();
                OdbcCommand cmd = Cn.CreateCommand();
                cmd.CommandText = "SELECT FirstName FROM TableUser WHERE Username = '" + userID + "'";
                OdbcDataReader reader = cmd.ExecuteReader();
                while (reader.Read())
                {
                   //how to return a string
                } 
            }

        }

        private void button1_Click(object sender, EventArgs e)
        {
            MessageBox.Show("My first name in database is: " + GlobalVariables.MyFirstName(Environment.UserName));

        }

Answer 1

For example :

public static string MyFirstName (string userID)
{
        string sReturnString = null;
    using (OdbcConnection Cn = new OdbcConnection(GlobalVariables.DatabaseConnectionString)) //Access database
    {
        Cn.Open();
        OdbcCommand cmd = Cn.CreateCommand();
        cmd.CommandText = "SELECT FirstName FROM TableUser WHERE Username = '" + userID + "'";
        OdbcDataReader reader = cmd.ExecuteReader();
        while (reader.Read())
        {
            sReturnString = (string)reader.GetValue(0);
            break;
        } 
     }
     return sReturnString;
}