C# Export DataSet to CSV and Download

 protected void exportToCSV_Click(object sender, EventArgs e)
    {
        if (exportToCSV.Visible && ViewState["data"] != null)
        {
            StringBuilder sb = new StringBuilder();
            DataTable dt = ((DataSet)ViewState["data"]).Tables[0];
 
            IEnumerable<string> columnNames = dt.Columns.Cast<DataColumn>().Select(column => column.ColumnName);
            sb.AppendLine(string.Join(",", columnNames));
 
            foreach (DataRow row in dt.Rows)
            {
                IEnumerable<string> fields = row.ItemArray.Select(field => string.Concat("\"", field.ToString().Replace("\"", "\"\""), "\""));
                sb.AppendLine(string.Join(",", fields));
            }
 
            Response.Clear();
            Response.ClearHeaders();
            Response.AddHeader("Content-Disposition", "inline;filename=TeachersBySchoolAndGrade.csv");
            Response.AddHeader("Content-Type", "application/Excel");
            Response.ContentType = "text/csv";
            Response.Write(sb);
            Response.Flush();
            Response.End();
        }
    }