Operation op = new Operation();
public string header = string.Empty;
protected void Page_Load(object sender, EventArgs e) 
{
    DataTable dt = op.queryMenu();
    if (dt != null && dt.Rows.Count > 0) 
    {
        StringBuilder sbHeader = new  StringBuilder();
        foreach(DataRow dr in dt.Rows) 
        {
            string menuID = string.Empty, menuTitle = string.Empty;
            if (dr["menuID"] != null) 
            {
                menuID = dr["menuID"].ToString();
            }
            if (dr["menuTitle"] != null) 
            {
                menuTitle = dr["menuTitle"].ToString();
            }
            sbHeader.AppendFormat("<a href='Category.aspx?menuID={0}' class='menu' target='_blank'>{1}</a>", menuID, menuTitle);
        }
        
        header = sbHeader.ToString();
    }
}