ASP.NET

<asp:DropDownList id="ddlcourseType" runat="server" 
                            onselectedindexchanged="ddlcourseType_SelectedIndexChanged" 
                            AutoPostBack="True">
                       <asp:ListItem Value="None">Please Select</asp:ListItem>
                       <asp:ListItem Value="Engl">English</asp:ListItem>
                       <asp:ListItem Value="Math">Math</asp:ListItem>
                       <asp:ListItem Value="Soci">Social Studies</asp:ListItem>
                       <asp:ListItem Value="Scie">Science</asp:ListItem>
                       <asp:ListItem Value="Hist">History</asp:ListItem>
                       </asp:DropDownList>

protected void ddlcourseType_SelectedIndexChanged(object sender, EventArgs e)
   {
       OleDbConnection dbConn = null;
       OleDbCommand dbCmd;
       OleDbDataReader dr;
       String strConnection;
       String strSQL;
       string path = Server.MapPath("eAcademy_DB.mdb");

       string Teachable = Convert.ToString(ddlcourseType.SelectedValue);
       strConnection = "PROVIDER=Microsoft.Jet.OLEDB.4.0;Data Source=" + path;
       dbConn = new OleDbConnection(strConnection);
       dbConn.Open();
       strSQL = "select * from tblEmployee where canTeach=" + Teachable;

       dbCmd = new OleDbCommand(strSQL, dbConn);
       DataSet ds = new DataSet();

       dbConn.Close();
       ddlTeacher.DataSource = ds;
       ddlTeacher.DataTextField = "emp_ID";
       ddlTeacher.DataValueField = "emp_ID";
       ddlTeacher.DataBind();
       ddlTeacher.Items.Insert(0, new ListItem("--Select--", "0"));
       if (ddlTeacher.SelectedValue == "0")
       {
           ddlTeacher.Items.Clear();
           ddlTeacher.Items.Insert(0, new ListItem("--Select--", "0"));
       }
   }

(o => o.LognName == name) 

Expression<Func<Users_UserAccount, bool>> whereLogonName = LinqExtender.DynamicLinq.BuildOrTree<Users_UserAccount, string>(LogonName, UserAccount => UserAccount.LogonName);

(o => o.LognName == name && o.LogonPW == "12345") //dumb pw

Expression.Or
Expression.And

public static Expression<Func<TValue, bool>> BuildOrTree<TValue, TCompareAgainst>(
        IEnumerable<TCompareAgainst> wantedItems,
        Expression<Func<TValue, TCompareAgainst>> convertBetweenTypes)
        {
            ParameterExpression inputParam = convertBetweenTypes.Parameters[0];

            Expression binaryExpressionTree = BuildBinaryOrTree(wantedItems.GetEnumerator(), convertBetweenTypes.Body, null);

            return Expression.Lambda<Func<TValue, bool>>(binaryExpressionTree, new[] { inputParam });
        }

private static Expression BuildBinaryOrTree<T>(
        IEnumerator<T> itemEnumerator,
        Expression expressionToCompareTo,
        Expression expression)
        {
            if (itemEnumerator.MoveNext() == false)
                return expression;

            ConstantExpression constant = Expression.Constant(itemEnumerator.Current, typeof(T));
            BinaryExpression comparison = Expression.Equal(expressionToCompareTo, constant);

            BinaryExpression newExpression;

            if (expression == null)
                newExpression = comparison;
            else
                newExpression = Expression.OrElse(expression, comparison);

            return BuildBinaryOrTree(itemEnumerator, expressionToCompareTo, newExpression);
        }