C / C++ / MFC

Quote:

_snwprintf_s and wprintf are not identifier.

Unable to cast object of type System.Data.DataColumn to type System.IConvertible

lblvol->Text=System::Convert::ToString(sqrt(System::Convert::ToDouble(dbdataset->Columns["DataReturn"])));

#include "math.h"

string dataReturn = dbdataset->Columns["DataReturn"]; // assuming this item is a string value
double doubleValue = System::Convert::ToDouble(dataReturn); // convert to double, but check for errors
double squareRoot = sqrt(doubleValue);
lblvol->Text = Convert::ToString(squareRoot);

Member 11230372 wrote:

Any idea why string type does not work from my side

Quote:http://www.cplusplus.com/reference/string/string/?kw=string[^]

The string class is an instantiation of the basic_string class template that uses char (i.e., bytes) as its character type, with its default char_traits and allocator types (see basic_string for more info on the template).

Error C2440: 'initializing' : cannot convert from 'System::Data::DataColumn ^' to 'double'

DataTable^dbdataset=gcnew DataTable();
                     DataColumn^rt_col=gcnew DataColumn();
                     rt_col->ColumnName = "DataRet";
                     rt_col->DataType=System::Type::GetType("System.Double");
                     dbdataset->Columns->Add(rt_col);

                     sda->Fill(dbdataset);

                     double varet = dbdataset->Columns["DataRet"]; //already double type, no need System::Convert::ToDouble
                     double vola = sqrt(varet);
                     lblvol->Text = Convert::ToString(vola);

Member 11230372 wrote:

it looks like a different story when dealing with c++/cli

Member 11230372 wrote:

Error C2440: 'initializing' : cannot convert from 'System::Data::DataColumn ^' to 'double'

int obs;
                     double mu, Ssigma, Svari, sum=0,sumsqr=0;

                     for (int i=1;i-1<dbdataset->Rows->Count-1;i++){
                         dbdataset->Rows[i-1]["DataRet"]=(System::Convert::ToDouble(dbdataset->Rows[i-1]["Population"])/System::Convert::ToDouble(dbdataset->Rows[i]["Population"])-1);
                         sum = sum + System::Convert::ToDouble(dbdataset->Rows[i-1]["DataRet"]);
                         obs = (dbdataset->Rows->Count-1);
                         mu = sum /obs;
                         sumsqr=sumsqr + pow((System::Convert::ToDouble(dbdataset->Rows[i-1]["DataRet"])-mu),2);
                         Svari=sumsqr/(obs-1);
                         Ssigma=sqrt(Svari);
                         lblvol->Text = Convert::ToString(Ssigma);