Cannot implicity convet type error : Sorry guys, I'm totaly new on this.

Trying to fill Combobox with data from a database and I'm using ExecuteReader as below, but when I try to instanciate my connection it shows me the error "Cannot implicity convet type error".

My BDConnect class code:


    public class DBConnect
    {
            private SqlConnection connection;
            private string servername = "10.1.76.109,1433";
            private string database = "EngLib";
            private string dbuser;
            private string userpassword;


            public DBConnect()
            {

            }

            public void doDBConnect(string dbuserform, string userpasswordform)
            {
                dbuser = dbuserform;
                userpassword = userpasswordform;
            }


            public void Initialize()
            {

            }

            public bool openConnection()
            {
                string connectionString;
                connectionString = "Server=" + servername + ";Database=" + database + ";user id=" + dbuser + ";Password=" + userpassword;
                Console.WriteLine(connectionString);
                connection = new SqlConnection(connectionString);
                try
                {
                    connection.Open();
                    return true;
                }
                catch (SqlException ex)
                {
                    switch (ex.Number)
                    {
                        case 0:
                            MessageBox.Show("Não é possível contactar o servidor. Entre em contato com o administrador");
                            break;

                        case 18456:
                            MessageBox.Show("Usuário/Senha inválidos, tente novamente");
                            break;
                    }
                    return false;
                }
 
    }

My form code:

    {
        public Form2()
        {
            InitializeComponent();
        }

        public void Form2_Load(object sender, EventArgs e)
        {
            SqlDataReader rdr = null;
            DBConnect sqlConnection;
            sqlConnection = new DBConnect();
            sqlConnection.doDBConnect(dbuserform: "usertest", userpasswordform: "usertest");
             {
                try
                {

                    {
                        sqlConnection.openConnection();
                        SqlCommand sqlCmd;
                        sqlCmd = new SqlCommand("SELECT Material FROM EngLib");
                        sqlCmd.Connection = sqlConnection;
                        SqlDataReader sqlReader = sqlCmd.ExecuteReader();

                        while (sqlReader.Read())
                        {
                            comboBox1.Items.Add(sqlReader["Material"].ToString());
                        }

                        sqlReader.Close();
                    }
                }
                finally
                {
                    // close the reader
                    if (rdr != null)
                    {
                        rdr.Close();
                    }

                }
            }
        }
    }
}

The user and password in the code is just temporary.


