var reportParameterCollection = new ReportParameter[3];
reportParameterCollection[0] = new ReportParameter { Name = "StartDate", Values = { DateTime.Now.AddDays(-3).ToShortDateString()} };
reportParameterCollection[1] = new ReportParameter { Name = "EndDate", Values = { DateTime.Now.ToShortDateString() } };
reportParameterCollection[2] = new ReportParameter { Name = "Customer_ID", Values = { 3 } };
reportViewer.ServerReport.SetParameters(reportParameterCollection);
reportViewer.ServerReport.Refresh();