Executing AddIndex tool to add attribute index in ArcGIS Engine

using ESRI.ArcGIS.Geoprocessor;
using ESRI.ArcGIS.Geoprocessing;
using ESRI.ArcGIS.DataManagementTools;

//Create new AddIndex tool
AddIndex addIndex = new AddIndex();
// Assign in_table to the shapefile you want to add attribute index for
addIndex.in_table = "MyShapeFile.shp";
addIndex.fields = "objectid;fid;";
addIndex.ascending = "ASCENDING";
addIndex.unique = "UNIQUE";
//Create new GeoProcessor instance
GeoProcessor cGP = new Geoprocessor();
cGP.SetEnvironmentValue("workspace", @"C:\temp");
cGP.Execute(addIndex, null);