Hi While computing a variance on my dataset, I end up with: error C2677: binary '+' : no global operator found which takes type 'System::Object ^const ' (or there is no acceptable conversion) The error message point to the line 65 of mean.hpp (see below piece of code). Can someone explain what's going wrong? Thanks template<typename Args> // line 59 void operator ()(Args const &args) //line 60 { // line 61 std::size_t cnt = count(args); // line 62 this->mean = numeric::fdiv( // line 63 (this->mean * (cnt - 1)) + args[parameter::keyword<Tag>::get()] // line 64 , cnt // line 65 ); // line 66 } // line 67 my code: #pragma once#include "stdAfx.h"#include "math.h"#include #include #include ..... accumulator_set< double, statstag::variance > acc_variance; DataRow^i; for (int i=1;i-1<dbdataset->Rows->Count-1;i++){ dbdataset->Rows[i-1]["DataRet"]=log(System::Convert::ToDouble(dbdataset- >Rows[i-1]["Pop"])/System::Convert::ToDouble(dbdataset->Rows[i]["Pop"])); acc_variance(dbdataset->Rows[i-1]["DataRet"]); lblvol->Text = Convert::ToString(sqrt(variance(acc_variance))); }